Everyday Math

Speed Distance Time Calculator

Calculate speed, distance, or time — enter any two values to find the third. Supports km/h, mph, and m/s.

The Speed, Distance, Time Triangle

Speed, distance, and time are related by a fundamental formula:

  • Speed = Distance ÷ Time
  • Distance = Speed × Time
  • Time = Distance ÷ Speed

This relationship is the basis of all kinematics problems in physics and practical navigation. Knowing any two values, you can always calculate the third.

Common Speed Units and Conversions

  • 1 km/h = 0.621 mph = 0.278 m/s
  • 1 mph = 1.609 km/h = 0.447 m/s
  • Speed of sound ≈ 343 m/s = 1,235 km/h = 767 mph (at sea level, 20°C)
  • Speed of light ≈ 299,792 km/s ≈ 1.08 billion km/h

Real-World Examples

  • Road trip: Driving 300 km at 100 km/h takes 3 hours
  • Running: A 5-minute-per-mile pace = 12 mph = 19.3 km/h
  • Marathon: 42.195 km — finishing in 4 hours requires an average speed of 10.55 km/h
  • Flight: A commercial flight at 900 km/h covering 9,000 km takes 10 hours

Frequently Asked Questions

How do I calculate speed from distance and time?
Speed = Distance ÷ Time. Make sure units are consistent: if distance is in km and time is in hours, the result is km/h. For example, 120 km ÷ 1.5 hours = 80 km/h.
How do I convert km/h to mph?
Multiply km/h by 0.621371. For example, 100 km/h × 0.621371 = 62.14 mph. To convert mph to km/h, multiply by 1.60934.
How long does it take to travel 100 km at 80 km/h?
Time = Distance ÷ Speed = 100 ÷ 80 = 1.25 hours = 1 hour and 15 minutes.
What is the average walking speed in km/h?
Average walking speed is approximately 4–5 km/h (2.5–3 mph). At 5 km/h, you cover 1 km in 12 minutes and 5 km in 60 minutes.