Redstone Comparator

A redstone comparator is a block that can produce an output signal from its front by reading chests, lecterns, beehives and similar blocks, or repeat a signal without changing its strength. It can also be set to either stop outputting a signal when its side input receives a stronger one (front torch off), or subtract its side input's signal strength from its output (front torch on).

Obtaining[]

Natural generation[]

Redstone comparators generate in ancient cities.

Breaking[]

A redstone comparator can be broken instantly with any tool, or by hand, and drops itself as an item.

Block	Redstone Comparator
Hardness	0
Breaking time (secs)
Default	0.05

A redstone comparator is removed and dropped as an item if:

• its attachment block is moved, removed, or destroyed;
• water flows into its space;‌^{[Java Edition only]}
• a piston tries to push it or moves a block into its space.

If lava flows into a redstone comparator's space, the redstone comparator is destroyed without dropping as an item.

Crafting[]

Ingredients	Crafting recipe
Redstone Torch + Nether Quartz + Stone

Usage[]

A redstone comparator can be placed on the top of any opaque block with a solid full-height top surface (including upside-down slabs and upside-down stairs). In Bedrock Edition, a comparator can also be placed on walls and fences. For more information about placement on transparent blocks, see Opacity/Placement.

The redstone comparator has a front and a back — the arrow on the top of the comparator points to the front. When placed, the comparator faces away from the player. The comparator has two miniature redstone torches at the back and one at the front. The back torches turn on when the comparator's output is greater than zero (the arrow on top also turns red). The front torch has two states that can be toggled by using the comparator:

• Down and unpowered (indicating the comparator is in "comparison mode")
• Up and powered (indicating the comparator is in "subtraction mode")

The redstone comparator can take a signal strength input from its rear as well as from both sides. Side inputs are accepted only from redstone dust, block of redstone, redstone repeaters, other comparators, and observers in specific scenarios. The redstone comparator's front is its output.

It takes 1 redstone tick (2 game ticks, or 0.1 seconds barring lag) for signals to move through a redstone comparator, either from the rear or from the sides. This applies to changing signal strengths as well as simply to turning on and off.

Redstone comparators check their power state before their scheduled ticks update. This results in redstone comparators not usually responding to 1-tick fluctuations of power or signal strength — for example, a 1-clock input is treated as always off from the side, and always on from the rear. This happens because the signal changes back to its original state before the redstone comparator checks its input states. However, certain setups such as powering any input with two separate observer pulses at the same time will cause a redstone comparator to respond to 2 gametick pulses.

The redstone comparator has four functions: maintain signal strength, compare signal strength, subtract signal strength, and measure certain block states (primarily the fullness of containers).

Maintain signal strength[]

A redstone comparator with no powered sides outputs the same signal strength as its rear input.

Compare signal strength[]

A redstone comparator in comparison mode (front torch down and unpowered) compares its rear input to its two side inputs. If either side input is greater than the rear input, the comparator output turns off. If neither side input is greater than the rear input, the comparator outputs the same signal strength as its rear input.

The formula for calculating the output signal strength is as follows:

output = rear × [left ≤ rear AND right ≤ rear]

Subtract signal strength[]

A redstone comparator in subtraction mode (front torch up and powered) subtracts the signal strength of the higher side input from the signal strength of the rear input.

output = max(rear − max(left, right), 0)

For example: if the signal strength is 6 at the left input, 7 at the right input and 4 at the rear, the output signal has a strength of max(4 − max(6, 7), 0) = max(4−7, 0) = max(−3, 0) = 0.

If the signal strength is 9 at the rear, 2 at the right input and 5 at the left input, the output signal has a strength of max(9 − max(2, 5), 0) = max(9−5, 0) = 4.

Measure block state[]

A redstone comparator treats certain blocks behind it as power sources and outputs a signal strength proportional to the block's state. The comparator may be separated from the measured block by an opaque block. However, in Java Edition, if the opaque block is powered to signal strength 15, then the comparator outputs 15 no matter the fullness of the container.^[1]

Fullness of containers[]

Minimum Items for Container Signal Strength

Containers
Total Slots	3	5	9	27	54	1
Power Level	Number of Items					Music Disc
0	0	0	0	0	0	No disc
1	1	1	1	1	1	"13"
2	14	23	42	1s 60	3s 55	"cat"
3	28	46	1s 19	3s 55	7s 46	"blocks"
4	42	1s 5	1s 60	5s 51	11s 37	"chirp"
5	55	1s 28	2s 37	7s 46	15s 28	"far"
6	1s 5	1s 51	3s 14	9s 42	19s 19	"mall"
7	1s 19	2s 10	3s 55	11s 37	23s 10	"mellohi"
8	1s 32	2s 32	4s 32	13s 32	27s	"stal"
9	1s 46	2s 55	5s 10	15s 28	30s 55	"strad"
10	1s 60	3s 14	5s 51	17s 23	34s 46	"ward"
11	2s 10	3s 37	6s 28	19s 19	38s 37	"11"
12	2s 23	3s 60	7s 5	21s 14	42s 28	"wait"
13	2s 37	4s 19	7s 46	23s 10	46s 19	"Pigstep"
14	2s 51	4s 42	8s 23	25s 5	50s 10	"Otherside" "Relic"
15	3s	5s	9s	27s	54s	"5"

A redstone comparator can output a signal indicating how full a container is. (0 for empty, 15 for full, etc.) The table on the right is described more in detail, later in this section.

Containers that can be measured by a comparator include:

• Furnace
• Blast Furnace
• Smoker
• Brewing Stand
• Hopper
• Minecart with Hopper on top of a detector rail
• Dispenser
• Dropper
• Chest
• Trapped Chest
• Minecart with Chest on top of a detector rail
• Barrel
• Large chest
• Large trapped chest
• Shulker Box (any color)

Generally speaking, the comparator output signal strength represents the average fullness of the slots, based on how many of that item form a full stack (64, 16, or 1 for non-stackable items).

The Minimum Items for Container Signal Strength table (right) shows the minimum full-stack-equivalent (FSE) to produce different signal strengths from common containers. A full-stack-equivalent quantifies how many normal 64-stackable items are needed to output a corresponding signal strength. The 's' is a constant 64, with the additional amount needed following after.

One may also consider the terms: cumulative-weight or weighted-sum instead of full-stack-equivalent.

Items that stack to a max of 16 (snowballs, signs, ender pearls, etc.), contribute +4 to the full-stack-equivalent for each unity (count of 1 item). Similarly, items that stack to 1 (minecart, boat, etc.) contribute +64, and items that stack to 64 contribute +1.

Example 1: 3 ender pearls will contribute a 3 x 4 = 12 full-stack-equivalent.

Example 2: 16 ender pearls and 60 redstone dust contributes a 16x4 + 60x1 = 124 full-stack-equivalent.

Example 3: 1 minecart and 60 redstone dust contributes a 1x64 + 60x1 = 124 full-stack-equivalent.

Example 4: To produce a signal strength of 10 from a hopper, one requires a full-stack-equivalent of at least 3s + 14 = 206 but strictly less than than 3s + 37 = 229. This can be done with 3 minecarts, and 14 dirt.

When a comparator measures a large chest or large trapped chest, it measures the entire large chest (54 slots), not just the half directly behind the comparator. A chest or trapped chest that cannot be opened (either because it has an opaque block, ocelot, or cat above it) always produces an output of 0 no matter how many items are in the container — shulker boxes can always be measured, even if they cannot open.

Calculating signal strength from items

When a container is empty, the output is off.

When it is not empty, the output signal strength is calculated as follows:

signal strength = floor(1 + ((sum of all slots' fullnesses) / (number of slots in container)) × 14)

fullness of a slot = number of items in slot / max stack size for this type of item

Example: 300 blocks in a dispenser (which has 9 slots), where each block stacks to a maximum of 64 has a 300 full-stack-equivalent. This produces an output with a signal strength of 8:

1 + ((300 items / 64 items per slot) / 9 slots) × 14 = 8.292, floored is 8

Calculating items from signal strength

It can be useful in redstone circuits to use containers with comparators to create signals of a specific strength. The number of items required in a container to produce a signal of desired strength is calculated as follows:

items required = max(desired signal strength, roundup((total slots in container × 64 / 14) × (desired signal strength − 1)))

Example: To use a furnace (which has 3 slots) to create a strength 9 signal, players need 110 items:

max(9, (3×64/14) × (9−1)) = 109.714, rounded up is 110

Miscellaneous[]

Some non-container blocks can also be measured by a redstone comparator:

Beehive and Bee nest

A hive or nest outputs a signal strength equal to the amount of honey in the hive/nest.

Cake

A cake outputs a signal strength relative to the amount of cake remaining. Each slice is worth 2 signal strength, with 7 total slices, for an output of 14 for a full cake.

Cauldron

A cauldron outputs different signal strengths depending on how much water or powdered snow is inside. From completely empty to completely full, the output values are 0, 1, 2, and 3. If lava or powder snow is inside, the strength is always 3.

Composter

A composter outputs different signal strengths depending on the level inside. From completely empty to completely full, the output values are 0, 1, 2, 3, 4, 5, 6, 7 and 8.

Command Block

A command block stores the "success count" of the last command executed, which represents the number of times the most recently used command of this command block succeeded. A "success" is defined by the command's success conditions: if a red error message is returned in the chat, the command was not successful.

Most commands can succeed once per execution, but certain commands (such as those that accept players as arguments) can succeed multiple times, and the comparator outputs the number of times it succeeded (maximum 15 when sent to redstone dust, but in the code it is able to go up to the 32-bit integer limit, and can be used in contraptions with no redstone dust with those values).

A command block continues to store the success count of the last command executed until it executes its command again, thus the comparator continues to output the same signal strength even after the command block is no longer being activated (it doesn't turn off when the signal to the command block turns off).

End Portal Frame

An end portal frame outputs a full signal of 15 if it contains an eye of ender and zero otherwise.

Item Frame

A comparator can measure the state of an item frame's contents. An item frame comparator outputs 0 if the item frame is empty, or 1 to 8 for any item depending on its rotation: 1 at initial placement, plus 1 for each 45° of rotation for a maximum of 8.

For an item frame that holds a map, a unit of rotation is 90° instead of 45°, but a comparator still outputs power levels 1 to 8. It takes two full rotations to cycle through all comparator outputs, and each orientation of the map corresponds to two output levels that differ by 4.

The comparator must be placed behind the block the item frame is attached to, facing away from the item frame. The block must be a full block, and the item frame cannot be submerged in water. Having a sign in the same block as the item frame will prevent the frame from sending a signal as well.‌^{[Java Edition only]}

Jukebox

A jukebox outputs a signal strength indicating which music disc is currently playing. See the Minimum Items for Container Signal Strength table above.

Lectern

A lectern outputs a signal strength that depends on what page the player is currently on. The calculation used is:

signal strength = floor(1 + ((current page - 1) / (number of pages in book - 1)) × 14)

This results in page 1 having a signal strength of 1, and the last page having a signal strength of 15. The exception is a single page book, which will output a signal strength of 15.

For example, a book with 15 pages will output a signal equal to the current page number. A book with 5 pages will output signal strengths of 1, 4, 8, 11 and 15 for the different pages. A book with 100 pages will have the signal strength increase to the next level on pages 1, 9, 16, 23, 30, 37, 44, 51, 58, 65, 72, 79, 86, 93 and 100.

Respawn Anchor

A respawn anchor outputs a signal strength of 0, 3, 7, 11, or 15, depending on the "charged" value.

Sculk Sensor

A sculk sensor outputs a signal strength depending on the type of vibration that is detected.

Chiseled Bookshelf

A chisled bookshelf outputs a signal strength between 1 and 6 indicating the last slot interacted with. When no slot has been interacted with yet, it outputs 0.

Sounds[]

Generic[]

Java Edition:

Sound	Subtitles	Source	Description	Resource location	Translation key	Volume	Pitch	Attenuation distance
	Block broken	Blocks	Once the block has broken	block.stone.break	subtitles.block.generic.break	1.0	0.8	16
	Block placed	Blocks	When the block is placed	block.stone.place	subtitles.block.generic.place	1.0	0.8	16
	Block breaking	Blocks	While the block is in the process of being broken	block.stone.hit	subtitles.block.generic.hit	0.25	0.5	16
	None[sound 1]	Entity-Dependent	Falling on the block with fall damage	block.stone.fall	None[sound 1]	0.5	0.75	16
	Footsteps	Entity-Dependent	Walking on the block	block.stone.step	subtitles.block.generic.footsteps	0.15	1.0	16

Bedrock Edition:

Sound	Source	Description	Resource location	Volume	Pitch
	Blocks	Once the block has broken	dig.wood	1.0	0.8-1.0
	Blocks	When the block is placed	dig.wood	1.0	0.8
	Blocks	While the block is in the process of being broken	hit.wood	0.23	0.5
	Players	Falling on the block with fall damage	fall.wood	0.4	1.0
	Players	Walking on the block	step.wood	0.3	1.0
	Players	Jumping from the block	jump.wood	0.12	1.0
	Players	Falling on the block without fall damage	land.wood	0.18	1.0

Unique[]

Java Edition:

Sound	Subtitles	Source	Description	Resource location	Translation key	Volume	Pitch	Attenuation distance
	Comparator clicks	Blocks	When a comparator is set to subtraction mode	block.comparator.click	subtitles.block.comparator.click	0.3	0.55	16
	Comparator clicks	Blocks	When a comparator is set to comparison mode	block.comparator.click	subtitles.block.comparator.click	0.3	0.5	16

Bedrock Edition:

Sound	Source	Description	Resource location	Volume	Pitch
	Blocks	When a comparator is set to subtraction mode	block.click	0.2	0.55
	Blocks	When a comparator is set to comparison mode	block.click	0.2	0.5

Data values[]

ID[]

Java Edition:

Name	Identifier	Form	Translation key
Redstone Comparator	comparator	Block & Item	block.minecraft.comparator

Name	Identifier
Block entity	comparator

Bedrock Edition:

Redstone Comparator	Identifier	Numeric ID	Form	Item ID[i 1]	Translation key
Unpowered block	unpowered_comparator	149	Block & Ungiveable Item[i 2]	Identical[i 3]	—
Powered block	powered_comparator	150	Block & Ungiveable Item[i 2]	Identical[i 3]	—
Item	comparator	522	Item	—	item.comparator.name

Name	Savegame ID
Block entity	Comparator

Block states[]

Java Edition:

Name	Default value	Allowed values	Description
facing	north	east north south west	The direction from the output side to the input side of the comparator, or the opposite from the direction the player faces while placing the comparator.
mode	compare	compare subtract	Specifies the current mode of the redstone comparator.
powered	false	false true	True if the redstone comparator is being powered.

Bedrock Edition:

Name	Metadata Bits	Default value	Allowed values	Values for Metadata Bits	Description
direction (Deprecated)	0x1 0x2	0	0 1 2 3	0 1 2 3	The direction the repeater directs power. 0: Facing north. 1: Facing east. 2: Facing south. 3: Facing west.
minecraft:cardinal_direction	Not Supported	south	east north south west	Unsupported	The direction from the output side to the input side of the comparator, or the opposite from the direction the player faces while placing the comparator.
output_lit_bit	0x8	false	false true	0 1	True if the redstone comparator is being powered.
output_subtract_bit	0x4	false	false true	0 1	Specifies the current mode of the redstone comparator.

Block data[]

A redstone comparator has a block entity associated with it that holds additional data about the block.

Java Edition:

Bedrock Edition:

See Bedrock Edition level format/Block entity format.

Advancements[]

Icon	Advancement	In-game description	Parent	Actual requirements (if different)	Resource location
	The Power of Books	Read the power signal of a Chiseled Bookshelf using a Comparator	Adventure	Place a comparator on any side of a chiseled bookshelf or the chiseled bookshelf against a comparator to trigger the advancement.	adventure/read_power_of_chiseled_bookshelf

Video[]

History[]

For a more in-depth breakdown of changes to repeater textures and models, including a set of renders for each state combination, see /Asset history

Java Edition
November 24, 2012					Jeb stated that there may be a "capacitor" in Minecraft.
December 27, 2012					Dinnerbone released pictures of the first version of the "comparator", stating it was a replacement for the "capacitor" idea that has variable, alternate inputs.
January 2, 2013					Dinnerbone released one more picture of the comparator. The picture itself showing a digital-to-analog converter, using the comparator as the main block.
1.5		13w01a			Added redstone comparators.
					Redstone comparators have 0 delay. At this point, block ID 149 was used for unpowered comparators, and block ID 150 for powered comparators.
		13w01b			A delay of 1 game tick (1⁄2 redstone tick) has now been added to redstone comparators to fix bugs.
					The ability to measure containers to redstone comparators has now been added.
		13w02a			The appearance of redstone comparators has now been changed - the top texture has changed to show quartz in the middle and the sides now use the smooth stone texture rather than the smooth stone slab side texture.
					The algorithm for measuring containers has now been changed so that redstone comparators output a signal with as few as 1 item in the container.
		13w02b			Redstone comparators now treat large chests as a single container.
		13w03a			Redstone comparators now output success count of command blocks.
					Redstone comparators now measure container minecarts on detector rails.
		13w04a			Redstone comparators now measure jukeboxes.
		13w05a			Redstone comparators no longer cause constant block updates. The delay has now been made consistent, and side input no longer causes a pulse output.
					Block 150 (later powered_comparator) is no longer used; powered state is now represented by the 8s bit on block 149 (later unpowered_comparator).
		13w05b			Redstone comparator delay has now been changed from 1 game tick (1/2 redstone tick) to 2 game ticks (1 redstone tick).
		13w09c			The redstone signal strength from a redstone comparator next to a brewing stand with 3 water bottles in it is now the same as one with 3 water bottles and 1 ingredient in it.
1.6.1		13w18a			Redstone comparators now measure cauldrons and end portal frames.
1.8		14w04a			Redstone comparators now measure item frames.
		14w10a			The torches under redstone comparators have now been shortened, which has changed the underside appearance from to .
		14w25a			The torches on comparators are now subject to ambient occlusion.
					Comparators set to subtract mode appear to be powered as well regardless of incoming power. The subtracting-only model still exists and can be achieved through /setblock.
		14w25b			The powered front torch when in subtraction mode is now lower.
					Comparators set to subtract by hand now appear normally again.
		14w28a			Redstone comparators now measure cakes.
1.9		15w42a			With the addition of the blaze powder fuel slot, brewing stands now have 5 slots instead of 4. Their original comparative power values from redstone comparators are listed below: Original values 0: 0 1: 1 2: 19 3: 37 4: 55 5: 1s 10 6: 1s 28 7: 1s 46 8: 2s 9: 2s 19 10: 2s 37 11: 2s 55 12: 3s 10 13: 3s 28 14: 3s 46 15: 4s
		15w47a			Redstone comparators' side inputs now take power from redstone blocks.
1.13		17w47a			All 3 IDs for the redstone comparator have now been merged into one ID: comparator.
					Redstone comparators now render their underside, which has changed their undersides from to .
					Prior to The Flattening, these blocks' numeral IDs were 149 and 150, and the item's 404.
					As a result, the formerly unused comparator ID is now technically used again, due to both unpowered and powered versions being merged into a single comparator block ID.
1.14		18w43a			The textures of redstone comparators have now been changed.
		19w02a			Redstone comparators now measure lecterns.
		19w03a			Redstone comparators now measure composters.
		19w12b			Redstone comparators can now be placed on glass, ice, glowstone and sea lanterns.
1.15		19w34a			Redstone comparators now measure how much honey is inside bee hives and bee nests.
1.16		20w06a			The way to calculate the input signals of redstone comparators has now been changed.
		20w11a			The changes to the way of calculating the input signals of redstone comparators from 20w06a have now been reverted.
		20w16a			Redstone comparators now measure Pigstep music discs in jukeboxes.
1.17		20w45a			Redstone comparators now measure lava cauldrons.
		20w46a			Redstone comparators now measure powder snow cauldron‌s.
1.18		21w41a			The texture of powered redstone comparator have now been changed.
1.19		22w13a			Redstone comparators now generate as part of ancient cities.
1.20 (Experimental)		22w42a			Redstone comparators now measure chiseled bookshelves.
1.20.2		23w33a			Redstone comparators now use stone sounds instead of wood sounds.[2]
Pocket Edition Alpha
v0.14.0		build 1			[verify] Added redstone comparators.
Pocket Edition
1.0.0		alpha 0.17.0.1			Redstone comparators now measure end portal frames.
1.0.5		alpha 1.0.5.0			Redstone comparators now output success count of command blocks.
1.1.0		alpha 1.1.0.0			Redstone comparators now measure shulker boxes.
Bedrock Edition
1.2.0		beta 1.2.0.2			Redstone comparators now measure jukeboxes.
					Redstone comparators now render their underside, which has changed their undersides from to
1.10.0		beta 1.10.0.3			The textures of redstone comparators have now been changed.
1.11.0		beta 1.11.0.1			Redstone comparators now measure smokers, blast furnaces, lecterns and composters.
1.18.10		beta 1.18.10.20			The texture of powered redstone comparator have now been changed.
1.20.30		beta 1.20.30.20			Redstone comparators now use the minecraft:cardinal_direction block state instead of direction.
Legacy Console Edition
TU19	CU7	1.12	Patch 1	1.0.1	[verify] Added redstone comparators.
TU31	CU19	1.22	Patch 3		Redstone comparators can now measure item frames.
		1.90			[verify] The textures of redstone comparators have now been changed.
New Nintendo 3DS Edition
0.1.0					[verify] Added redstone comparators.

Redstone comparator "items"[]

The following content is transcluded from Technical blocks/Redstone Comparator.

Java Edition
1.5		13w01a			Redstone comparators have extra, unobtainable item forms corresponding to their block IDs. They can be obtained via the /give command or inventory editors with numeric item IDs 149 and 150.
1.7.2		13w37a			The direct item forms of redstone comparators have been removed from the game. They can no longer exist as items in any way, only as placed blocks.
Pocket Edition Alpha
?					Redstone comparators probably exist as an item.

Appearances[]

Unpowered Comparator[]

Java Edition
1.5		13w01a			The unpowered comparator item uses this texture in inventories, when held in first or third person view, as a dropped item or when in an item frame
		13w02a			The unpowered comparator item now uses this texture in inventories, when held in first or third person view, as a dropped item or when in an item frame.
					This is due to major texture storage changes in this version.

Powered Comparator[]

Java Edition
1.5		13w01a			The powered comparator item uses this texture in inventories, when held in first or third person view, as a dropped item or when in an item frame
		13w02a			The powered comparator item now uses this texture in inventories, when held in first or third person view, as a dropped item or when in an item frame.
					This is due to major texture storage changes in this version.
Bedrock Edition
?					Powered comparators use this texture.[3]
?					Powered comparators use this texture.[4]

Names[]

Unpowered Comparator[]

Java Edition

• 13w01a - 13w25b: [Has no defined name, rendering a minimum-length text box if highlighted]
• 13w25c - 13w36b: tile.comparator.name

When given using the /give command, it is announced as tile.comparator.name.

Powered Comparator[]

Java Edition

• 13w01a - 13w25b: [Has no defined name, rendering a minimum-length text box if highlighted]
• 13w25c - 13w36b: tile.comparator.name

When given using the /give command, it is announced as tile.comparator.name.

Issues[]

Issues relating to "Redstone Comparator" are maintained on the bug tracker. Report issues there.

Trivia[]

• Comparators do not emit redstone particles when powered, unlike redstone torches and repeaters.^[5]

Gallery[]

• 

  Dinnerbone showing how comparators work.

• 

  Dinnerbone showing how comparators work.

• 

  Dinnerbone showing how comparators work.

• 

  A contraption incorporating comparators.

• 

  Comparators in action.

• 

  Output specific signals.

• 

  Another comparator in use.

• 

  Rotating the torch in the item frame adjusts the comparator's output.

References[]