Read engine RPM
straight from the sound.

No OBD adapter. No clip-on sensor. No wiring. Point your phone's microphone at the engine and RPMCalc gives you a live digital and analog RPM reading — for any cylinder count, 2-stroke or 4-stroke.

Download on the App Store See how it works

RPMCalc reading 3450 RPM on a 4-cylinder 4-stroke engine — Live reading, updated in real time

RPMCalc home screen with cylinder and cycle settings — Set your engine, then listen

RPMCalc reading a 6-cylinder 2-stroke engine at 5820 RPM — 1–12 cylinders, 2-stroke or 4-stroke

Why RPMCalc

Any engine configuration

Dial in 1 to 12 cylinders and 2-stroke or 4-stroke — RPMCalc listens for the exact firing frequency that combination produces.

Accurate to the nearest RPM

A real-time digital readout under the needle shows the exact number, backed by a classic analog tachometer dial.

Freeze any reading

Tap Freeze to hold a value on screen for as long as you need, then Resume to go live again.

Auto-Freeze for working alone

Set a delay, prop the phone by the exhaust, and go rev the engine yourself — the reading freezes automatically and waits for you.

Works fully offline

Every bit of audio analysis happens on your device. No internet connection required, ever.

Nothing recorded, nothing shared

No accounts, no ads, no analytics. Audio is processed in memory and never stored or transmitted.

Built For

Car and motorcycle engines · small engines (mowers, chainsaws, generators, go-karts) · boat motors · anyone who needs an RPM reading and doesn't have a tachometer wired in.

Get RPMCalc

One screen. No clutter. Just point, listen, and read the number.

Download on the App Store

Read engine RPMstraight from the sound.