Speed Calculator

Speed, distance, and time: how the triangle formula works

Speed, distance, and time are three quantities that are always mathematically related by the formula: speed equals distance divided by time. If you know any two of these values, the third can always be calculated. This is sometimes taught as the "speed triangle" in schools, where covering any one of the three reveals the formula for that unknown. This speed calculator automates all three variations so you never need to rearrange the formula manually.

When you select "Distance and time," the calculator divides distance by time to give speed. When you select "Speed and time," it multiplies speed by time to give distance. When you select "Speed and distance," it divides distance by speed to give time. In each case, all values are converted to a common unit system (kilometres and hours as the base) before the arithmetic runs, so mixing input units never produces a wrong answer.

The result always shows speed in three units: km/h (kilometres per hour), mph (miles per hour), and m/s (metres per second). Distance is shown in kilometres and miles. Time is shown as hours, minutes, and seconds in h:mm:ss format. This makes the output useful regardless of which unit system you work in.

Common practical uses include working out average speed during a drive or run, estimating how far you can travel in a given time at a certain speed, or figuring out how long a journey will take at a known average speed. The calculator handles decimal inputs, so values like 1.5 hours or 42.195 km (marathon distance) are fully supported.

Unit conversions used in this calculator

All unit conversions in this calculator use standard, internationally recognised factors. One mile equals exactly 1.60934 kilometres, so mph to km/h uses that multiplier and km/h to mph divides by it. Metres per second to km/h multiplies by 3.6 (since 1 m/s = 3600 m per hour = 3.6 km per hour). Metres as a distance unit are divided by 1,000 to convert to kilometres before any speed calculation runs.

Time entry uses three separate fields for hours, minutes, and seconds, so you can enter any combination. If you leave a time field blank, it is treated as zero. For example, entering 1 hour and 30 minutes gives a total time of 90 minutes or 5,400 seconds. The output time uses the same h:mm:ss format so you can read it as a clock duration rather than a raw decimal.

Worked examples

A car travels 250 km in 2 hours and 30 minutes. Total time in hours is 2.5. Speed = 250 / 2.5 = 100 km/h = 62.14 mph = 27.78 m/s. A runner runs at 12 km/h for 45 minutes (0.75 hours). Distance = 12 x 0.75 = 9 km = 5.59 miles. A cyclist wants to cover 30 miles at 15 mph. Time = 30 / 15 = 2 hours = 2h 00m 00s. These examples illustrate how the calculator can serve very different scenarios from the same interface.

When using this tool for travel planning, remember that the speed entered should be an average speed, not a top speed. Real journeys involve acceleration, deceleration, stops, and varying road conditions. The calculator assumes constant speed throughout the journey, which is a simplification. For more precise travel time estimates, factor in rest stops and variable traffic conditions separately.