whatisrpm.com

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RPM to mph

Reviewed08·2026

Engine speed becomes road speed through three numbers you can look up: the gear ratio, the final drive, and the tire's rolling circumference. The tool below runs the whole chain and prints its working.

By Oliver Wakefield-Smith. Written by Oliver Wakefield-Smith, who maintains the reference tables on this site against manufacturer and standards-body documents.

63.3mph

wheel rpm = 3,000 ÷ (0.9 × 3.9) = 854.7
tire dia = 16″ × 25.4 + 2 × (205 × 55%) = 632 mm; circumference = 1.985 m
speed = 854.7 × 1.985m × 60 ÷ 1609.344 = 63.3 mph

The chain, step by step

wheel rpm = engine rpm ÷ (gear ratio × final drive)
3,000 ÷ (0.9 × 3.9) = 3,000 ÷ 3.51 = 854.7 wheel rpm
tire 205/55R16: dia = 406.4 + 2 × 112.75 = 631.9 mm; circ = π × 0.6319 = 1.985 m
speed = 854.7 × 1.985 × 60 ÷ 1,609.344 = 63.3 mph

Rotation-to-speed relations of this shape are standard mechanical engineering reference material Engineering ToolBox2026-08; gear ratios and final drives are published per model in manufacturer technical specifications, which is where the worked example's 0.9 fifth gear and 3.9 final drive stand in for your car's actual figures.

Reading a tire sidewall

205/55R16 encodes width 205 mm, aspect ratio 55% (sidewall height as a share of width), rim 16 inches. Diameter = rim + two sidewalls; the tool does this arithmetic from the three fields. Real rolling circumference runs a little smaller under load, so treat outputs as close estimates, not calibration.

Why gearing is the interesting variable

Run the tool at fixed speed across your car's ratios and you get its cruising-RPM map: the same 70 mph might sit at 3,400 rpm in fourth and 2,300 in sixth. That map is the mechanical background to RPM and fuel economy and shift points: gearing decides where the needle lives at any speed, and your right foot only chooses among the gears.

Questions this page keeps getting

How do I convert engine RPM to mph?

Divide engine RPM by the gear ratio and final drive to get wheel RPM, multiply by the tire's circumference to get distance per minute, then convert: multiply by 60 and divide by 1,609.344 for mph.

How do I get my tire's circumference from the sidewall size?

For 205/55R16: sidewall height is 205 mm x 0.55 = 112.75 mm. Diameter is the 16 inch rim (406.4 mm) plus two sidewalls, 631.9 mm. Circumference is pi times that, about 1.985 m.

Why does the same RPM give different speeds in different gears?

The gear ratio is in the denominator of the chain: a shorter (numerically higher) gear turns the wheels fewer times per engine revolution, so identical engine RPM produces lower road speed.