MyRPMCalc

Point your phone at a running engine and read its RPM instantly — no OBD adapter, no clip-on inductive sensor, no wiring. RPMCalc listens through your microphone and calculates engine speed straight from the sound of the exhaust or the engine itself. HOW IT WORKS Every engine's exhaust note has a fundamental firing frequency set by its cylinder count, stroke cycle, and RPM. RPMCalc analyzes that frequency in real time and converts it to a live RPM reading — accurate to the nearest 1 RPM on the digital readout, with a classic analog tachometer dial for an at-a-glance feel. BUILT FOR ANY ENGINE - Set any cylinder count from 1 to 12 - Choose 2-stroke or 4-stroke cycle - Works on cars, motorcycles, lawn mowers, generators, chainsaws, go-karts, boats, and other small engines WORK ALONE, HANDS-FREE Diagnosing an engine is usually a two-person job — one to rev it, one to watch the gauge. RPMCalc's Auto-Freeze feature fixes that. Set a delay (5 to 30 seconds), tap Start Listening, prop the phone near the exhaust, and walk to the driver's seat. RPMCalc automatically freezes the reading after your chosen delay so it's waiting for you, unchanged, when you walk back. A manual Freeze/Resume button is also there any time you want to hold a reading on the spot. SIMPLE, FOCUSED, NO CLUTTER One screen. No accounts, no ads, no subscriptions, no clutter. Just a tachometer, a couple of settings, and a listen button. PRIVACY RPMCalc processes audio entirely on your device. Nothing is recorded, uploaded, or shared. PLEASE NOTE RPMCalc estimates engine speed acoustically and is not a certified or calibrated tachometer. Background noise, wind, and exhaust modifications can affect accuracy. Don't rely on it as the sole basis for safety-critical decisions like redline limits or tuning — always follow your engine or equipment manufacturer's official guidance.