KPH to m/s Converter

Common questions

What is 100 km/h in m/s?

27.7777777778 m/s: a car at 100 km/h covers a little under 28 metres in every second. The speeds either side of it come out as 90 km/h is 25 m/s exactly, 110 km/h is 30.5555555556, 120 km/h is 33.3333333333 and 130 km/h is 36.1111111111. Going back, 30 m/s is 108 km/h.

What is the formula for km/h to m/s?

m/s = km/h x 1000 / 3600, which reduces to km/h / 3.6, or the exact fraction km/h x 5 / 18. The converter stores a kilometre per hour as 1/3.6 metres per second and works from there, so both directions use the same number: km/h = m/s x 3.6. Press swap and 1 m/s gives 3.6 km/h, 10 m/s gives 36 and 25 m/s gives 90.

How do I convert km/h to m/s in my head?

Multiply by 5 and divide by 18, since 5/18 is exactly 1/3.6. For 90 km/h that is 450 / 18 = 25 m/s, and for 72 km/h it is 360 / 18 = 20 m/s. A rougher route is to divide by 4 and add a bit back: 100 / 4 is 25, and the true answer is 27.7777777778, about 11 percent higher, so the quarter rule undershoots by a tenth every time.

Which speeds convert to a whole number of m/s?

The multiples of 3.6. 3.6 km/h is 1 m/s, 18 is 5, 36 is 10, 72 is 20, 90 is 25 and 108 is 30, so a physics question written with those numbers was set to come out clean. Anything else repeats: 5 km/h, a walking pace, is 1.38888888889 m/s, 20 km/h is 5.55555555556 and 50 km/h is 13.8888888889.

Why do physics problems want m/s rather than km/h?

Because the metre and the second are the SI base units, so a speed in m/s drops straight into v = d / t, into an acceleration in m/s squared and into a kinetic energy in joules without a second conversion. That is the whole job of this page: read the speed off a sign or a dashboard in km/h, convert once, and keep working in metres and seconds.

Is the conversion exact, or is it rounded?

The relationship is exact: a kilometre is defined as 1,000 metres and an hour as 3,600 seconds, so the factor of 3.6 is a definition and not a measurement. What is rounded is the printing. 1 km/h in metres per second is a repeating decimal, so the page shows 0.277777777778, which is the value cut at twelve significant digits. The arithmetic behind it runs at full double precision.

How do I get mph, knots or ft/s at the same time?

They are already there. Under the headline the page lists the same speed in every other unit it holds for speed, each with its own Copy button, so 100 km/h reads 62.1371192237 mph, 53.9956803456 knots and 91.1344415281 feet per second alongside its 27.7777777778 m/s. Pick any of them in the To menu to promote it to the headline instead.

Can I convert m/s back to km/h here?

Yes, in one press. The swap button between the two boxes reverses the pair and the page becomes an m/s to km/h converter: 1 m/s is 3.6 km/h, 5 m/s is 18, 25 m/s is 90 and 343 m/s, roughly the speed of sound in air, is 1,234.8 km/h. Both unit menus stay open throughout, so you can send the same figure to knots or feet per second without leaving.

Why does the page open on km/h and m/s when I last converted something else?

Because this page is named for that pair, so it sets it on arrival ahead of the pair the converter remembered. It does not overwrite the main unit converter's memory, which is still on the pair you left it on. The value in the box does carry over, since the number you were last working on is usually the one you still want.

Does anything I type leave the browser?

No. The speed table ships with the page as constants, the division happens as you type, and there is nothing to upload and no account to make. Once the page has loaded it keeps working without a connection.