Quick Answer
- Engine rpm = mph x 336.13 x axle ratio x gear ratio / tire diameter in inches. For 275/65R18 tires (32.1 in), a 3.73 axle and a 0.636 overdrive gear at 70 mph that is 1,740 rpm.
- To go the other way, mph = rpm x tire diameter / (336.13 x axle x gear). With the same setup, 2,000 rpm is 80.4 mph.
- A taller tire lowers rpm at a given speed and a numerically higher axle ratio raises it. The tables below show both effects.
Engine rpm = mph x 336.13 x axle ratio x gear ratio / tire diameter in inches.
Gear ratio is the transmission ratio of the gear you want (for example 1.000 direct, 0.636 for a 10th gear overdrive). For a transfer case or low range, multiply it in.
Engine rpm
1,740
Wheel rpm
734
Tire diameter
32.07 in
Working
70.0 x 336.13 x 3.73 x 0.636 / 32.07 = 1,740
Get a plain-English explanation of your results and what they mean for your vehicle.
Engine RPM at 50 to 80 mph by Gear
Example setup: Ford F-150 10-speed automatic ratios, 275/65R18 tires (32.07 in) and a 3.73 axle. Use the calculator for your own tire, axle and gearbox.
| Gear | Ratio | 50 mph | 60 mph | 65 mph | 70 mph | 75 mph | 80 mph |
|---|---|---|---|---|---|---|---|
| 1st | 4.696 | 9,178 | 11,014 | 11,932 | 12,849 | 13,767 | 14,685 |
| 2nd | 2.985 | 5,834 | 7,001 | 7,584 | 8,168 | 8,751 | 9,335 |
| 3rd | 2.146 | 4,194 | 5,033 | 5,453 | 5,872 | 6,291 | 6,711 |
| 4th | 1.769 | 3,457 | 4,149 | 4,495 | 4,840 | 5,186 | 5,532 |
| 5th | 1.520 | 2,971 | 3,565 | 3,862 | 4,159 | 4,456 | 4,753 |
| 6th | 1.275 | 2,492 | 2,990 | 3,240 | 3,489 | 3,738 | 3,987 |
| 7th | 1.000 | 1,954 | 2,345 | 2,541 | 2,736 | 2,932 | 3,127 |
| 8th | 0.854 | 1,669 | 2,003 | 2,170 | 2,337 | 2,504 | 2,671 |
| 9th | 0.689 | 1,347 | 1,616 | 1,751 | 1,885 | 2,020 | 2,155 |
| 10th | 0.636 | 1,243 | 1,492 | 1,616 | 1,740 | 1,865 | 1,989 |
Gear ratios: Ford 2024 F-150 Technical Specifications (10-speed SelectShift automatic). Rpm values are calculated and do not include torque converter slip.
RPM to MPH Chart by Gear
Speed in mph at each engine rpm for the same example setup (275/65R18, 3.73 axle). Multiply by 1.609 for km/h.
| Gear | Ratio | 1,000 rpm | 1,500 rpm | 2,000 rpm | 2,500 rpm | 3,000 rpm | 4,000 rpm | 5,000 rpm | 6,000 rpm |
|---|---|---|---|---|---|---|---|---|---|
| 1st | 4.696 | 5.4 | 8.2 | 10.9 | 13.6 | 16.3 | 21.8 | 27.2 | 32.7 |
| 2nd | 2.985 | 8.6 | 12.9 | 17.1 | 21.4 | 25.7 | 34.3 | 42.9 | 51.4 |
| 3rd | 2.146 | 11.9 | 17.9 | 23.8 | 29.8 | 35.8 | 47.7 | 59.6 | 71.5 |
| 4th | 1.769 | 14.5 | 21.7 | 28.9 | 36.2 | 43.4 | 57.8 | 72.3 | 86.8 |
| 5th | 1.520 | 16.8 | 25.2 | 33.7 | 42.1 | 50.5 | 67.3 | 84.2 | 101.0 |
| 6th | 1.275 | 20.1 | 30.1 | 40.1 | 50.2 | 60.2 | 80.3 | 100.3 | 120.4 |
| 7th | 1.000 | 25.6 | 38.4 | 51.2 | 64.0 | 76.7 | 102.3 | 127.9 | 153.5 |
| 8th | 0.854 | 30.0 | 44.9 | 59.9 | 74.9 | 89.9 | 119.8 | 149.8 | 179.7 |
| 9th | 0.689 | 37.1 | 55.7 | 74.3 | 92.8 | 111.4 | 148.5 | 185.6 | 222.8 |
| 10th | 0.636 | 40.2 | 60.3 | 80.4 | 100.6 | 120.7 | 160.9 | 201.1 | 241.3 |
How Tire Size and Axle Ratio Change RPM at 70 mph
Engine rpm at 70 mph in 10th gear (0.636) for different tires and axle ratios, with the change from the 275/65R18 on a 3.73 axle (1,740 rpm).
| Tire | Diameter | 3.31 axle | 3.55 axle | 3.73 axle | 4.10 axle |
|---|---|---|---|---|---|
| 245/70R17 | 30.5" | 1,624 (-7%) | 1,742 (+0%) | 1,830 (+5%) | 2,011 (+16%) |
| 265/70R17 | 31.6" | 1,567 (-10%) | 1,681 (-3%) | 1,766 (+1%) | 1,941 (+12%) |
| 275/65R18 | 32.1" | 1,544 (-11%) | 1,656 (-5%) | 1,740 (+0%) | 1,913 (+10%) |
| 275/60R20 | 33.0" | 1,501 (-14%) | 1,610 (-7%) | 1,692 (-3%) | 1,860 (+7%) |
| 33x12.50R17 (example) | 33.0" | 1,501 (-14%) | 1,610 (-7%) | 1,691 (-3%) | 1,859 (+7%) |
| 35x12.50R20 (example) | 35.0" | 1,415 (-19%) | 1,518 (-13%) | 1,595 (-8%) | 1,753 (+1%) |
Tire sizes marked example are not Ford sizes. The effective gear ratio calculator shows what a tire change does to the ratio and the speedometer error calculator what it does to the gauge.
Engine RPM Formulas: RPM, MPH, Gear and Axle Ratio
Engine rpm from speed
rpm = mph x 336.14 x axle ratio x gear ratio / tire diameter (in). For 70 mph, 3.73, 0.636 and 32.07 in: 1740 rpm.
Speed from engine rpm
mph = rpm x tire diameter (in) / (336.14 x axle x gear). For 2,000 rpm: 80.4 mph. Multiply by 1.609 for km/h.
Where 336.13 comes from
1 mph is 5,280 x 12 / 60 = 1,056 inches per minute, and one wheel turn covers pi x diameter inches, so wheel rpm = mph x 1,056 / (pi x diameter) = mph x 336.13 / diameter.
Overall gear ratio
Axle (final drive) ratio x transmission ratio of the gear you want x any transfer case ratio. A larger overall ratio means more engine revolutions per wheel revolution.
Wheel rpm
Engine rpm / overall ratio, or mph x 336.13 / diameter. At 70 mph on 32.07 in tires the wheels turn 734 rpm.
Comparing two setups
New rpm = old rpm x (new overall ratio / old overall ratio) x (old diameter / new diameter). The table below applies this to common tire and axle changes.
Wheel revolutions per mile for any tire are on the revolutions per mile calculator.
How to Use the Engine RPM Calculator
- 1Enter your tire size (for example 275/65R18 or 35x12.50R20), the axle ratio and the transmission ratio of the gear you want.
- 2In Engine RPM at a Speed, enter the road speed in mph or km/h to get the rpm and the wheel rpm.
- 3In RPM to MPH, enter an engine rpm to get the speed in mph and km/h for that tire, axle and gear.
- 4Check the axle ratio on the axle tag or in the owner's manual and the gear ratios in the specifications, then compare setups with the tables.