Speed Calculator

What Is Speed?

Speed is how fast something changes position — the distance it covers per unit of time. The SI unit is meters per second (m/s), but everyday life uses kilometers per hour (km/h), miles per hour (mph) and feet per second (ft/s) depending on the country and the situation. This speed calculator uses the speed–distance–time relationship: enter any two of the three values and it finds the third.

The Speed, Distance and Time Formulas

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

Increase the distance in the same time, or cover a fixed distance in less time, and speed goes up. Units must agree before you calculate: if speed is in m/s, time should be in seconds and distance in meters. Riding a bike at 10 m/s for one minute (60 s) covers 10 × 60 = 600 m.

Worked Example

Usain Bolt's 100m world record of 9.58 seconds works out to 10.44 m/s — about 37.6 km/h or 23.4 mph, sustained over the full sprint.

Average Speed vs. Instantaneous Speed

The result here is an average speed over the whole trip — total distance divided by total time. Your instantaneous speed, the reading on a speedometer at one moment, changes constantly with traffic, hills and stops. A 120 km drive that takes two hours averages 60 km/h even if you spent some of it at 100 km/h and some stopped at lights.

Speed vs. Velocity

Speed only says how fast; velocity also says in which direction. A car circling a track at constant speed keeps changing velocity because its direction keeps changing. For basic trip planning, speed is all you need.

Everyday Uses

• Estimating how long a trip will take for a given distance and average speed.
• Working out the pace you need to hit a running or cycling goal.
• Checking whether a delivery or flight time is realistic.
• Solving physics and math homework problems.

To convert a result between units, use the Unit Conversion Calculator, and see the Gas Mileage Calculator or Fuel Cost Calculator to price a trip.