Speed · Distance · Time

What is the speed-distance-time relationship?

Speed, distance, and time are linked by one fundamental formula: Distance = Speed multiplied by Time. If you know any two of these values, you can always calculate the third. This relationship governs everything from daily commutes to space travel, and is one of the first physics concepts taught in school.

Speed measures how fast an object moves — the distance covered per unit of time. Common units include kilometers per hour (km/h), miles per hour (mph), and meters per second (m/s). Average speed is the total distance divided by total time, while instantaneous speed is the speed at any specific moment.

The three formulas

• Distance = Speed multiplied by Time. How far you go at a given speed for a given duration.
• Speed = Distance divided by Time. How fast you must go to cover a distance in a given time.
• Time = Distance divided by Speed. How long it takes to cover a distance at a given speed.

How to use this tool

Select which value you want to calculate (speed, distance, or time), enter the two known values with their units, and the result appears instantly. The tool supports multiple unit systems — switch between km/h and mph, kilometers and miles, or hours, minutes, and seconds using the unit selectors.

Common examples

• Driving 80 km/h for 2.5 hours covers 200 km.
• A 350 km trip at 110 km/h takes about 3 hours and 11 minutes.
• Running 10 km in 50 minutes means a pace of 12 km/h.
• A flight covering 3,500 km in 4 hours travels at an average speed of 875 km/h.

Practical tips

Remember that average speed is not the average of two speeds. If you drive 60 km/h for the first half of a trip and 120 km/h for the second half, your average speed is 80 km/h, not 90 km/h (because you spend more time at the slower speed). This is a common mistake in homework problems and real-world trip planning.

When planning road trips, account for stops, speed limits, and traffic. A 500 km highway trip at an average of 100 km/h should take 5 hours of driving, but with fuel stops, meals, and rest breaks, plan for 6–7 hours total travel time.

Worked example

A cyclist covers 45 km in 1 hour 30 minutes. Convert the time to hours (1.5) and divide: 45 / 1.5 = 30 km/h average speed. To find distance instead, multiply: at 30 km/h for 2 hours you travel 60 km. For time, divide distance by speed: 90 km at 30 km/h takes 3 hours. Keeping units consistent — all kilometres and hours, or all metres and seconds — is the key to a correct answer.

Common mistakes

The most common mistake is mixing units, such as dividing kilometres by minutes and reporting the result as km/h. Convert everything to a single system first. Another is averaging two speeds directly: driving 60 km at 30 km/h then 60 km at 60 km/h does not average to 45 km/h, because you spend more time at the slower speed. Use total distance divided by total time instead.

Frequently asked questions

How do I convert between km/h and mph?

Multiply km/h by 0.6214 to get mph, or multiply mph by 1.6093 to get km/h. Quick approximation: km/h divided by 1.6 gives roughly mph. So 100 km/h is approximately 62 mph.

What is the difference between speed and velocity?

Speed is a scalar quantity — it only measures how fast something moves. Velocity is a vector quantity — it includes both speed and direction. A car driving at 60 km/h north has a velocity; 60 km/h alone is its speed. For most everyday calculations, speed is sufficient.

How do I convert between km/h and m/s?

Divide km/h by 3.6 to get m/s, or multiply m/s by 3.6 to get km/h. For example, 36 km/h / 3.6 = 10 m/s. The factor comes from 1,000 metres per kilometre divided by 3,600 seconds per hour.