Gear Ratio Calculator & RPM

Two tooth counts in, gear ratio, RPM, and torque out. Know the ratio you need? Cog finds the real tooth pairs that make it.

Type two tooth counts. Gear Ratio Calculator & RPM hands back the gear ratio, output RPM, and mechanical advantage before you lift your thumb — then tells you in plain English whether that pair multiplies torque or trades it for speed.

Most ratio tools stop at the division. It also works backwards: enter the ratio you actually need, and it searches real tooth counts from 8T to 96T, ranks the closest practical pairs, flags the exact matches, and drops your pick straight into the calculator. Finish by naming the setup so the whole drivetrain comes back with one tap.

WHAT YOU GET • The right ratio the first time — driving and driven teeth become ratio, output RPM, and mechanical advantage live as you type • A clear answer on torque versus speed, with the exact multiplier spelled out so you know what the pair will actually do • Real gears for a target ratio — the reverse solver lists the closest tooth pairs, exact or a stated percent off, for reduction or overdrive • A 24-gear reference you can search — spur, helical, bevel, planetary, and worm, each with tooth count, use case, and the ratios it makes with every other gear in the catalog • Your drivetrains on file — name a setup, add notes, edit it later, and recall the full pair and RPM in a tap • Answers at the bench with no signal — every number is worked out on your iPhone, no account or sign-in

PERFECT FOR • Cyclists comparing a climbing gear to a sprint gear before a ride • Robotics and RC builders matching a motor to the speed and torque a mechanism needs • Machinists and maintenance techs sizing a reducer for a motor shaft • Students and tinkerers learning why a worm drive self-locks and a planetary set stays compact

WHY NOT JUST USE A SPREADSHEET OR A WEB CALCULATOR? A spreadsheet gives you one number and leaves the interpretation to you. A web page needs a connection and forgets everything you entered. This app explains the result, solves the problem in reverse when you know the ratio first, keeps a reference of common gear types with you, and remembers every setup you have ever saved.

PRIVATE BY DEFAULT Your setups and calculations stay on this device. It has no account, no ads, no tracking, and works fully offline.

FULL ACCESS This app is unlocked with a subscription or a one-time purchase: choose weekly, yearly, or lifetime. Subscriptions renew automatically unless cancelled at least 24 hours before the end of the current period, and payment is charged to your Apple ID account at confirmation of purchase. Manage or cancel anytime in your App Store account settings.

Enter your first pair and see the ratio land.

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