Top Speed by Gear Calculator (Speed from RPM)
What is my top speed in each gear? Enter the engine speed you want to test (the redline, for example), up to six gear ratios, the final drive and the tire, as a diameter or a code such as 205/55R16. You get a speed for every gear in one table. For the engine rpm at a cruising speed in a single gear, the RPM at speed calculator is quicker.
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Formula
tire diameter (in) = 2 x width (mm) x aspect % / 25.4 + rim (in)for a metric code such as 205/55R16wheel rpm = engine rpm / (gear ratio x final drive)speed (mph) = wheel rpm x pi x diameter (in) x 60 / 63360km/h = mph x 1.609344
Assumptions: no slip, nominal tire diameter, rpm measured at the crankshaft. Gears set to 0 are treated as not fitted.
Worked example
205/55R16 tire: 2 x 205 x 0.55 / 25.4 + 16 = 24.88 in. At 6000 rpm with a 3.42 final drive:
| Gear | Ratio | Speed (mph) |
|---|---|---|
| 1 | 3.62 | 35.9 |
| 2 | 2.19 | 59.3 |
| 3 | 1.41 | 92.1 |
| 4 | 1.00 | 129.8 |
| 5 | 0.83 | 156.4 |
| 6 | 0.69 | 188.2 |
Use this when
You want speed by gear: planning shift points, checking whether a gear set reaches a target speed at the redline, or comparing two final drives across the whole box. Because the output is a table, it is the right page for the question "how fast is each gear".
Use another calculator instead when
- You know the speed and want the engine rpm in one gear: use the RPM at speed calculator.
- You need the axle ratio from ring and pinion teeth: use the gear ratio calculator.
- You want to compare tire sizes: use the tire size calculator.
Common mistakes
- Reading the top number as a real top speed. It is the speed at the rpm you entered, not what the car can pull against drag.
- Entering gear ratios as speeds, or leaving an unused gear at a non-zero value.
- Using the overall diameter in mm; the diameter field is in inches.
Frequently asked questions
How do I calculate speed from rpm?
Divide engine rpm by the gear ratio and by the final drive to get wheel rpm, then multiply by the tire circumference. Example: 6000 rpm in a 1.0 gear with a 3.42 final drive and a 24.88 inch tire gives 1754 wheel rpm, which is about 129.8 mph.
How do I read a tire size such as 205/55R16?
205 is the width in millimetres, 55 is the sidewall height as a percentage of the width, and 16 is the rim diameter in inches. The overall diameter is 2 x 205 x 0.55 / 25.4 + 16 = 24.88 inches.
Why is the real speed different from the calculated speed?
The calculation assumes no wheel slip, no clutch or converter slip and a tire that keeps its nominal diameter. Tire wear, load and speed change the rolling radius by a percent or two, and speedometers read slightly high by design. Treat the number as a close estimate.
What do I enter for a car with fewer than six gears?
Fill in gear 1 and as many further gears as the car has, and leave the rest at 0. Unused gears are shown with a dash. A 5-speed with gear 5 at 0.83 reaches 156.4 mph at 6000 rpm with the default final drive and tire, if the engine can pull it.
What is my top speed in each gear at the redline?
Enter the redline as the engine speed and your own ratios. With the default 6-speed, a 3.42 final drive and 205/55 R16 tires, 6000 rpm gives 35.9 mph in first, 92.1 mph in third and 188.2 mph in sixth. Real top speed is usually lower because drag and power run out before the limiter.
How do I calculate speed in km/h for each gear?
Set the speed unit to km/h and the table converts each gear for you. With 225/40 R18 tires, the default ratios and 6500 rpm, first gear is 63.1 km/h and fourth gear is 228.3 km/h. Each value is wheel rpm times tire circumference, converted from miles per hour at 1.609344 km per mile.
How do I use this for a 4-speed gearbox?
Fill in the four ratios and leave gears 5 and 6 at 0, and they show a dash. With ratios 3.58, 2.02, 1.35 and 0.98, a 4.10 final drive, a 25 inch tire and 7000 rpm, fourth gear gives 129.6 mph and first gear 35.5 mph.