BeginnerRedstone
Redstone basics in Minecraft: dust, repeater, comparator, observer
A Redstone Comparator (3 Redstone Torches, 1 Nether Quartz, 3 Stone) takes a signal from behind and another from the sides.
×1 Tested 26.3 Block
Redstone Comparator block in Minecraft
The Redstone Comparator reads signals and containers. It compares or subtracts two redstone signals, and placed behind a chest, hopper, furnace or other block with contents, it outputs a signal that grows with how full it is.
It is made with the Crafting Table from 3 × Redstone Torch, 3 × Stone and Nether Quartz.
What it does
A comparator has a main input at the back and side inputs. In compare mode, it passes the rear signal through unless a side signal is stronger. Click it to light its front torch and switch to subtract mode, where it outputs the rear signal minus the strongest side signal.
Its most used trick is measuring blocks: behind a container it gives a signal from 0 to 15 depending on how many items are inside, the basis of item sorters, full-chest alarms and automatic farms. It also reads a cake's slices, a composter's level, the disc in a jukebox, the rotation of an item in a frame, a cauldron's level and the last book slot used in a Chiseled Bookshelf.
It is crafted from three redstone torches, a nether quartz and three stone, which means a trip to the Nether before you can build one.
How to craft
Crafting table 
3 × Redstone Torch + Nether Quartz + 3 × Stone → Redstone Comparator
// Slots with several items cycle through every accepted option.
How Redstone Comparator connects
1 links · from the 26.3 game dataAdvancements
The Power of BooksRead the power signal of a Chiseled Bookshelf using a ComparatorTutorials with Redstone Comparator (5)
All tutorials with Redstone Comparator →×1 Tested 26.3 IntermediateRedstone
How to build an item sorter in Minecraft
Behind each filter hopper, place a block one level lower, then a Redstone Comparator on it, pointing away from the hopper (layers 3 and 4).
×4 Tested 26.3 IntermediateRedstone
How to make hidden doors in Minecraft
Behind that block, in the corridor wall, place a Redstone Comparator pointing away from the wall, then a Redstone Repeater in front of it, then a solid block (layer 5).
×1 Tested 26.3 BeginnerSurvival
How to make a Copper Golem and sort items with it
A Redstone Comparator reads a different signal for each pose, and the statue keeps its pose when you break it (a pickaxe is fastest).
Tested 26.3
Block states
| mode | compare · subtract |
|---|---|
| facing | north · south · west · east |
| powered | true · false |
Tags
#minecraft:washed_away_by_fluids
Redstone Comparator · FAQ
How do you get Redstone Comparator in Minecraft?
At the Crafting Table: 3 × Redstone Torch, 3 × Stone and 1 × Nether Quartz give 1 × Redstone Comparator. Mining the block drops it.
What is Redstone Comparator used for in Minecraft?
It compares or subtracts redstone signals and measures how full containers and other blocks are.
Can a piston move Redstone Comparator?
No: when a piston pushes it, it breaks and drops as an item.
Which advancements involve Redstone Comparator?
The Power of Books (Read the power signal of a Chiseled Bookshelf using a Comparator).