Speed Distance Time Calculator
Solve for speed, distance, or time using the fundamental relationship: Distance = Speed × Time.
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How to use this calculator
Set the unknown to 0 and the calculator solves for it using D = S × T.
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Enter two known values (distance, speed, or time).
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Set the unknown value to 0.
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The calculator solves for the missing quantity.
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Results are shown in both km and miles.
Frequently asked questions
How do I convert km/h to m/s?
Divide by 3.6. 90 km/h ÷ 3.6 = 25 m/s. Conversely, multiply m/s by 3.6 to get km/h. 30 m/s × 3.6 = 108 km/h. This conversion is essential in physics problems that use SI units.
What is average speed vs instantaneous speed?
Average speed = total distance / total time. Instantaneous speed is speed at a precise moment (shown on a speedometer). A car averaging 90 km/h over 3 hours covered 270 km total, but its speed varied throughout the journey.
How do I calculate travel time with stops?
Calculate driving time using D/S, then add stop time separately. Total trip time = driving time + stop time. The calculator computes driving time only — stops must be added manually.
What is the difference between speed and velocity?
Speed is scalar (magnitude only): 90 km/h. Velocity is vector (magnitude + direction): 90 km/h north. Average speed uses total distance; average velocity uses displacement (straight-line distance from start to end). They differ when direction changes.
Speed, distance, and time calculations
The speed-distance-time triangle
Cover the unknown in the triangle to get its formula: cover D → D = S × T; cover S → S = D/T; cover T → T = D/S. This mnemonic is taught in schools worldwide and works for any consistent set of units (km + km/h + hours, or miles + mph + hours).
Relative speed
When two objects move in the same direction, relative speed = |S₁ − S₂|. When moving toward each other (opposite directions), relative speed = S₁ + S₂. If a train at 80 km/h overtakes another at 60 km/h, the relative speed is 20 km/h. These problems are common in competitive exams.
Speed in physics vs everyday use
Physics uses metres per second (m/s) in SI units. Daily life uses km/h (most countries) or mph (USA, UK). Sound travels ~343 m/s (1,234 km/h) at sea level. Light travels ~300,000 km/s. An airliner cruises at ~900 km/h — less than 0.001% the speed of light.
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