# What is the average speed?

Computes average speed from distance and time, or the distance covered or the time taken from the other two, in any units.

- Page: https://www.acalculator.org/physics/speed-calculator
- JSON spec: https://www.acalculator.org/physics/speed-calculator.json
- Version: dad0ab85947d

## Default answer

Example with the default inputs (Distance 150 mi, Time 2.5 h): Covering 150 mi in 2.5 h is an average speed of 60 mph.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| d | Distance | The distance travelled. |
| t | Time | The time taken to cover the distance. |
| s | Average speed | The average speed: distance divided by time. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| distance | Distance | The distance travelled. |
| time | Time | The time taken to cover the distance. |
| speed | Average speed | The average speed: distance divided by time. |

## Method

speed = distance ÷ time; distance = speed × time; time = distance ÷ speed.

## Assumptions

- The speed is the average over the whole trip. It says nothing about the speed at any one moment.
- Units are converted exactly: 1 mi = 1,609.344 m, 1 ft = 0.3048 m, 1 nautical mile = 1,852 m (NIST SP 811).

## Worked examples

1. d = 241,401.6, t = 9,000 gives s = 26.8224. Source: hand calculation in content.mdx: 150 mi ÷ 2.5 h = 60 mph = 60 × 1,609.344 m ÷ 3,600 s = 26.8224 m/s (NIST SP 811: 1 mi = 1,609.344 m).
2. s = 27.777778, t = 2,700 gives d = 75,000. Source: hand calculation in content.mdx: 100 km/h × 0.75 h = 75 km.
3. d = 42,195, s = 5 gives t = 8,439. Source: hand calculation in content.mdx: 42,195 m ÷ 5 m/s = 8,439 s = 2 h 20 min 39 s.

## FAQ

### What is the formula for speed?

Average speed = distance ÷ time. For example, 150 miles in 2.5 hours is 150 ÷ 2.5 = 60 miles per hour.

### How do I work out distance from speed and time?

Multiply them: distance = speed × time. At 100 km/h for 45 minutes (0.75 h) you cover 100 × 0.75 = 75 km. Put the time in the same unit as the speed first (hours for km/h or mph).

### How do I work out the time from distance and speed?

Divide the distance by the speed: time = distance ÷ speed. A 42.195 km marathon at 5 m/s takes 42,195 ÷ 5 = 8,439 seconds, which is 2 hours, 20 minutes and 39 seconds.

### What is the difference between speed and average speed?

Speed at one moment is what a speedometer shows. Average speed is the total distance divided by the total time, including slow parts and stops. This calculator gives the average speed.

### How do I convert mph to km/h?

Multiply by 1.609344, because one mile is exactly 1,609.344 meters. 60 mph is 96.56 km/h. Pick another unit next to the speed box to see it converted.

## Sources

- NIST Special Publication 811 (2008), Guide for the Use of the International System of Units, Appendix B.8: 1 mi = 1,609.344 m, 1 ft = 0.3048 m, 1 nautical mile = 1,852 m, 1 h = 3,600 s. https://www.nist.gov/pml/special-publication-811
- World Athletics, Competition Rules, Rule 55 (road races): the marathon is 42.195 km. https://worldathletics.org/about-iaaf/documents/book-of-rules