Speed, Time, Distance

Pick what to find, enter the two known values with their units — you get the formula, the SI unit conversion with an explanation, and the substitution. The answer comes in convenient units.

The one formula of motion. All three problems are the same formula S = v · t turned different ways: distance is speed times time, speed is distance over time, time is distance over speed. The classic trap is units: with kilometers and minutes mixed together, convert everything to one system first. The calculator does that for you and shows how.

FAQ

How do you convert km/h to m/s?

Divide by 3.6. A kilometer is 1000 meters and an hour is 3600 seconds, so km/h · 1000/3600 = km/h / 3.6. For example, 72 km/h = 20 m/s. To go back, multiply by 3.6.

Why convert units to one system?

The formula S = v · t only works with consistent units: speed in m/s and time in seconds give meters. Plugging km/h together with minutes produces nonsense. The safest route is SI: meters and seconds.

How do you remember what divides by what?

The classic triangle: S on top, v and t below. Cover the unknown — what remains shows the formula: cover S and you see v · t; cover v and you see S over t, i.e. S / t.

What is average speed and what is the catch?

Average speed is the whole distance divided by the whole time — not the arithmetic mean of speeds. Drive half the route at 60 km/h and half at 40 km/h, and the average is 48, not 50: the slow half takes longer.