How the Speed Calculator Works
Speed, distance and time are linked by one simple rule. If you know two of them, you can find the third. The Speed Calculator does this for you. It works with the units that you use, gives the time in hours, minutes and seconds, and shows the answer in other units too.
The formula
Speed is how far you go in a unit of time:
speed = distance / time distance = speed x time time = distance / speed
These are the same rule written three ways. If you cover the value you want in a triangle with distance at the top, and speed and time at the bottom, the other two show you what to do: divide the top by the bottom, or multiply the bottom two.
What you enter
- What you want to find: the speed, the distance or the time.
- The distance, in kilometers, miles, meters, feet or nautical miles.
- The time, in hours, minutes and seconds. You do not have to change 1 hour 30 minutes into 1.5 hours.
- The speed, in km/h, mph, m/s or knots.
A worked example: speed
You drive 100 kilometers in 1 hour and 30 minutes.
| Step | Result |
|---|---|
| Time in hours (1 + 30 / 60) | 1.5 hours |
| Speed (100 / 1.5) | 66.67 km/h |
| In miles per hour (66.67 / 1.609344) | 41.42 mph |
| In meters per second (66.67 / 3.6) | 18.52 m/s |
| In knots (66.67 / 1.852) | 36 knots |
This is an average speed. It does not say how fast you were going at any moment. You could have been going 100 km/h on the highway and 30 km/h in the town.
More examples
| You know | You find | Calculation | Answer |
|---|---|---|---|
| 60 mph for 2 hours 30 minutes | Distance | 60 x 2.5 | 150 miles |
| 500 km at 80 km/h | Time | 500 / 80 | 6.25 hours = 6:15:00 |
| 240 nautical miles at 12 knots | Time | 240 / 12 | 20 hours |
| 100 meters in 9.58 seconds | Speed | 100 / 9.58 x 3.6 | 37.58 km/h |
| 42.195 km in 3 hours 30 minutes | Speed | 42.195 / 3.5 | 12.06 km/h |
- You know: 60 mph for 2 hours 30 minutes
You find: Distance
Calculation: 60 x 2.5
Answer: 150 miles - You know: 500 km at 80 km/h
You find: Time
Calculation: 500 / 80
Answer: 6.25 hours = 6:15:00 - You know: 240 nautical miles at 12 knots
You find: Time
Calculation: 240 / 12
Answer: 20 hours - You know: 100 meters in 9.58 seconds
You find: Speed
Calculation: 100 / 9.58 x 3.6
Answer: 37.58 km/h - You know: 42.195 km in 3 hours 30 minutes
You find: Speed
Calculation: 42.195 / 3.5
Answer: 12.06 km/h
Time for a trip at different speeds
How long does a trip of 100 kilometers take?
| Speed | Time |
|---|---|
| 20 km/h (cycling) | 5 hours |
| 50 km/h (town) | 2 hours |
| 80 km/h | 1 hour 15 minutes |
| 100 km/h | 1 hour |
| 120 km/h | 50 minutes |
20 km/h ████████████████████████████████████████ 5 h 50 km/h ████████████████ 2 h 80 km/h ██████████ 1 h 15 min 100 km/h ████████ 1 h 120 km/h ███████ 50 min
Going faster saves less and less time. Going from 100 to 120 km/h saves only 10 minutes on a trip of 100 kilometers.
The graph
The calculator draws a graph of the distance against the time. At a steady speed it is a straight line. The steeper the line, the faster you go. The dots mark each quarter of the trip.
Average speed is not the average of the speeds
This is a common mistake. Suppose you drive 60 km at 60 km/h, and another 60 km at 40 km/h. The mean of the two speeds is 50 km/h, but the real average speed is different:
| Part | Distance | Speed | Time |
|---|---|---|---|
| First part | 60 km | 60 km/h | 1 hour |
| Second part | 60 km | 40 km/h | 1.5 hours |
| Whole trip | 120 km | 48 km/h | 2.5 hours |
Part 1 ████████████████████████████████████████ 60 km/h Part 2 ███████████████████████████ 40 km/h Mean of the two (wrong) █████████████████████████████████ 50 km/h True average ████████████████████████████████ 48 km/h
The true average is the total distance divided by the total time: 120 / 2.5 = 48 km/h. You spend more time at the slow speed, so it counts more. Use the calculator with the total distance and the total time to get it right.
Pace
Runners often use pace, which is the time for one kilometer or one mile. It is the inverse of speed. A speed of 12 km/h is a pace of 5:00 per kilometer. The marathon example, 42.195 km in 3 hours 30 minutes, is a pace of 4:59 per kilometer, or 8:01 per mile. The calculator shows both.
Tips
- Use the same units. A distance in kilometers and a time in hours give a speed in km/h. The calculator changes the units for you.
- Enter the time in hours, minutes and seconds. A time of 1.5 hours is 1 hour 30 minutes, not 1 hour 50 minutes.
- Remember the stops. For a trip, use the total time, with the stops, for the average speed of the trip, and the time when you are moving for the average speed of moving.
- Nautical miles are longer than miles. One nautical mile is 1,852 meters, and a mile is 1,609 meters.
What this calculator does not include
- Changing speed. It works with a steady or an average speed, and does not include acceleration.
- The direction of movement, or the speed of one object relative to another.
- Traffic, wind, weather and other things that change the real time of a trip.
This tool gives an estimate for general information only. Real trips depend on the road, the traffic and the weather.