Estimate engine RPM from road speed, tire diameter or size code, axle ratio, and transmission gear. See cruise RPM before a re-gear — free, no signup.
Enter a size code to auto-calc diameter, or type overall diameter in inches.
Use 1.0 for direct/top gear; overdrive is often ~0.7–0.8.
2470
Engine RPM
32.99"
Tire diameter used
Many vehicles cruise near 1,800–2,200 RPM on the highway. Higher RPM usually means more noise and fuel use.
100% browser-based
Runs locally in this tab
No upload required
Your files never leave this device
Nothing is stored
Close the tab and the input is gone
Instant results
No queue and no server wait
Enter road speed (1–300 mph), tire overall diameter or a size code, axle (ring-and-pinion) ratio, and the transmission ratio for the gear you care about (1.00 is direct drive; overdrive is below 1). The result is engine RPM: how fast the crank turns at that cruise, which is what you need before taller tires or a 4.10 swap.
Paste 285/70R17 or type the diameter from Tire Size Calculator. RPM falls when diameter rises: a 35-inch tire at the same axle turns slower than a 31 at 70 mph. Diameter is clamped to a sensible light-truck range so a typo does not look like 900 RPM at highway speed.
You set transmission ratio for the gear you are modelling. To see 6th versus 4th, change that field; the tool does not load a 10-speed map. Formula: RPM = speed × axle × trans × 336.13 / diameter(inches), using inches per mile over 60π.
No ECU log and no upload. Speed, ratio, and diameter stay in the tab. Close the page and they are gone. This ignores slip, tire growth at speed, and converter stall — it is geometric RPM, not a dyno. Nothing is stored on a server.
Use the cruise you care about (for example 70). The field is miles per hour, not km/h.
A code such as 275/65R18 is parsed to overall diameter. Or type inches from the size calculator.
Axle is ring ÷ pinion (3.73). Trans is the gear you are in: 1.0 for 1:1, ~0.7 for a typical overdrive.
Compare to your redline and to where the engine makes torque. Recalculate after a tire or gear change with the new diameter or axle.
Straight answers on privacy, limits, and how the workspace behaves.
More from Auto.
Look up OE bolt pattern, tire size, offset, and center bore by year, make, and model — then check if an aftermarket wheel and tire setup fits. No VIN.
Auto
Enter a metric or flotation tire size to get overall diameter, section width, sidewall, circumference, and revolutions per mile. Free, instant, no signup.
Auto
Compare two tire sizes side by side: diameter, width, sidewall, ride height, and rev/mile, plus Preferred ±2% or Acceptable ±3% fitment bands — free online.
Auto
Convert metric sizes like 275/60R20 to flotation such as 35x12.50R20 and back. See the exact equivalent and nearest catalog match — free, private, in-browser.
Auto
See how a taller or shorter tire changes indicated speed. Get actual speed, percent error, and a 25–75 mph table from stock vs new size — free, private.
Auto
Convert indicated odometer miles into real distance after a tire diameter change. See actual miles, percent error, and the diameter ratio — free, private.
Auto