# Transmission Speed Calculator

URL: https://speedycalculator.com/calculators/physics/transmission/
Last updated: 2026-10-30

> The transmission speed calculator finds a vehicle's road speed from engine rpm, transmission gear ratio, final drive (differential) ratio and tyre diameter.

## Inputs

- Engine speed (rpm)
- Transmission gear ratio
- Final drive (differential) ratio
- Tyre diameter (in, mm, cm, ft, m)

## Results

- Vehicle speed
- Wheel speed
- Engine rpm per 100 km/h

## Formula

```
v = rpm × π × tyre diameter / (gear ratio × final drive ratio)
```

## Explanation

Gears translate engine revolutions into wheel speed. Knowing the speed in each gear at the redline or at cruising rpm helps choose ratios for racing, towing or economy.

### How to use the Transmission Speed Calculator

- **Engine speed (rpm)**
- **Transmission gear ratio**
- **Final drive (differential) ratio**
- **Tyre diameter**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Enter the engine rpm, the gear ratio, the final drive ratio and the overall tyre diameter.

### Inputs explained

FieldWhat to enterEngine speed (rpm)A numberTransmission gear ratioA numberFinal drive (differential) ratioA numberTyre diameterUnits: in, mm, cm, ft, m

### What each result means

- **Vehicle speed** = [Engine speed (rpm)]÷60×pi×[Tyre diameter]÷([Transmission gear ratio]×[Final drive (differential) ratio])
- **Wheel speed** = [Engine speed (rpm)]÷([Transmission gear ratio]×[Final drive (differential) ratio])
- **Engine rpm per 100 km/h** = 100÷3.6÷(pi×[Tyre diameter])×60×[Transmission gear ratio]×[Final drive (differential) ratio]

### Example values

How the main result changes when **Engine speed** changes and everything else stays at the example values above:

Engine speed (rpm)Vehicle speed (km/h)1,50050.062,25075.093,000100.11993,750125.14994,500150.17996,000200.2399

## Worked example

Inputs — Engine speed (rpm): 3,000; Transmission gear ratio: 1; Final drive (differential) ratio: 3.73; Tyre diameter: 26 in.

Results — **Vehicle speed = 100.1199 km/h**; Wheel speed = 804.29 rpm; Engine rpm per 100 km/h = 2,996 rpm.

## Key terms

- **Final drive**: The differential gear reduction.

## FAQ

**How do I find tyre diameter from its size?**
Use our tyre size calculator, or diameter = rim + 2 × width × aspect ratio.

**What does a lower final drive do?**
A numerically higher ratio gives more acceleration but lower top speed per rpm.

**Does tyre wear change the speed?**
Slightly – worn tyres are a little smaller.

**Why does the speedometer differ?**
Many read a few percent high by design.


## Sources

- [OpenStax – University Physics Volume 1](https://openstax.org/details/books/university-physics-volume-1)
- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)