Gear Ratio Calculator

See engine rpm in every gear at your cruise speed, speed per 1000 rpm, and the top speed your gearing allows at redline.

Final drive ratio

Tire size or diameter in inches

Redline

rpm

Cruise speed

mph

Gears

Speed unit

Gear Ratios

Gear	Ratio	Overall

Accuracy: rpm figures assume no tire slip and no torque-converter slip, so manual gearboxes and locked-up automatics land within a few percent in the real world. An automatic with an open converter cruises several hundred rpm higher than shown. The top speed column is what the gearing allows at redline - in the tallest gears most cars run out of power or aerodynamics long before they run out of gear. This column answers the gearing-limited question; the top speed calculator answers the power-limited one, and your real ceiling is whichever of the two is lower.

How the numbers are calculated

Engine rpm is speed x 336.135 x final drive ratio x gear ratio / tire diameter in inches. The 336.135 constant is 63,360 inches per mile divided by 60 minutes and pi - an exact unit conversion, not a fitted number. Every value in the table comes from that one formula or its inverse: overall ratio is gear times final drive, speed per 1000 rpm and top speed at redline are the same relationship solved for speed. Shift-drop rpm is the redline times the next gear's ratio over the current one - it shows how far the tach falls on each upshift.

Default values are the factory drivetrain of the 1997-2004 Corvette C5 6-speed, whose roughly 1,500 rpm at 70 mph in 6th is a widely published figure you can check the table against. Not sure of your tire diameter? The tire size calculator computes it from the size printed on the sidewall.

Enter Drivetrain Details

Gear Ratios

RPM per Gear Results

RPM versus Speed Chart

How the numbers are calculated