How to Make a Redstone Comparator in Minecraft

Guide Java Bedrock

Quick answer: Craft a redstone comparator with 3 redstone torches, 1 nether quartz and 3 stone. It reads how full containers are, compares and subtracts signal strengths, and preserves power levels instead of boosting them.

What you need

Redstone torch x3
Nether quartz x1
Stone x3 (smelted, not cobblestone)
Crafting table

Step by step

Smelt cobblestone into 3 stone and craft 3 redstone torches (redstone dust over sticks).
Craft the comparator: 3 stone across the bottom row, nether quartz in the center, redstone torches above it and at the middle-left and middle-right.
Face it right: the arrow on top points to the output side - the comparator faces away from you when placed.
Measure containers: point the back at a chest, hopper, furnace, barrel, composter, lectern, jukebox, cake or bee nest and it outputs a signal that scales with how full or complete it is.
Compare mode (front torch down): the comparator outputs the back input only if it is at least as strong as the side inputs - a minimum-signal gate.
Subtract mode: use the placed comparator once and the front torch pops up. Now it outputs the back signal MINUS the strongest side signal - analog arithmetic for smart circuits.
Preserve levels: unlike a repeater, a comparator passes the exact input strength through (up to 15), which keeps fullness readings and analog lines intact.
Build classics: item-fullness alarms, auto-smelter controls, composter harvest triggers and secret lectern-page doors all run on comparators.

Java vs Bedrock

Recipe and both modes work the same in Java and Bedrock. One placement perk: in Bedrock, comparators can also sit on walls and fences.

Versions: Added in 1.5 (13w01a) with the Redstone Update - the same snapshot that introduced the daylight detector and the redstone block era of analog circuitry.

Frequently asked questions

What does a comparator do in Minecraft?

Three jobs: it measures how full a container is and outputs that as signal strength, it compares a back input against side inputs, and in subtract mode it outputs their difference. It passes signal strength through unchanged instead of resetting it to 15.

What is the difference between a repeater and a comparator?

A repeater boosts any signal back to full 15, adds delay and works as a one-way diode. A comparator keeps the exact signal level, measures container fullness, and can compare or subtract signals - but adds no delay and cannot lock.

How do you detect a full chest in Minecraft?

Place a comparator with its back against the chest. Its output scales with fullness - a full double chest outputs 15. Wire that to a lamp, note block or piston door for a fullness alarm or overflow shutoff.