How this instrument works
A metre per second serves as SI's coherent unit for speed, and neither half of it depends on a physical artefact. One second means 9,192,631,770 periods of a caesium-133 hyperfine transition, fixed in 1967. One metre means how far light travels in 1/299,792,458 of that second — a definition adopted in 1983, when the speed of light stopped being measured and became a decreed exact value.
Kilometres per hour blends two counting habits. A kilometre holds 1000 metres by decimal prefix; an hour holds 3600 seconds because Babylonian astronomers carved days and circles into sixties, an inheritance Europe never dropped. Divide 3600 by 1000 and 3.6 falls out. BIPM lists hours among non-SI units accepted for use alongside SI, which is why km/h stays respectable on a road sign despite never being coherent.
Which unit you meet depends on trade. Anemometers, wind-turbine power curves, ballistics tables, Beaufort-scale definitions: all speak m/s — a large turbine cuts in near 3, reaches rated output around 12, then feathers its blades near 25 m/s. Road signs, public forecasts, car speedometers across most of Europe, Asia, Africa, Latin America: all use km/h. Britain and America keep mph; pilots and mariners keep knots. Converting usually translates an instrument's language into a listener's.
- Type your reading into Metres per second (m/s); 10 comes preloaded, about a fresh breeze at sea.
- Read Kilometres per hour (km/h) directly beneath — it recomputes as you type, with no button to press.
- Working backwards from a km/h figure? Divide it by 3.6 first, then type that result here to check yourself.
- Sanity-check against an anchor worth memorising — 10 m/s is 36 km/h, so 5 becomes 18 while 20 becomes 72.
Worked example — an anemometer reading 10 m/s
A coastal weather station logs wind at 10 m/s, which is what its cup anemometer reports natively. Type 10 into Metres per second (m/s) and Kilometres per hour (km/h) answers 36.0, because 10 × 3.6 = 36 with nothing hiding in a trailing digit.
Keep that pair in mind as a reference point. Thirty-six km/h means force 5 on Beaufort, a brisk cycling pace, roughly what a sprinter averages down 100 metres. Halve your entry to 5 m/s and output halves to 18.0 km/h; double it to 20 and you get 72.0. Straight-line factors behave that obligingly.
Questions
Is 3.6 exact, or has it been rounded?
Exact. An hour holds 3600 seconds, a kilometre holds 1000 metres, both by definition rather than by measurement, so 3600 ÷ 1000 = 3.6 with nothing left over. Multiplying a m/s value by 3.6 preserves every significant figure you began with; any imprecision in your answer arrived from your instrument, never from this arithmetic.
How do I convert km/h back into m/s?
Divide by 3.6. Some figures land neatly — a 90 km/h limit becomes exactly 25 metres per second — while others repeat forever, since 1 ÷ 3.6 = 0.2777…, so 100 kilometres per hour works out at 27.777… Round once at the end, quoting no more digits than your original reading justified. Handy check on yourself: 36 km/h is precisely 10 m/s.
Which way round does 3.6 go?
Multiply to reach km/h; divide to reach m/s. For one given motion, kilometres per hour always reads numerically larger — a 100 km/h limit works out at 27.8 m/s, not 360. Reversing this ranks as by far the commonest slip in speed work, so test any result against the 10 m/s = 36 km/h anchor before quoting it.
Why do meteorologists use m/s when road signs use km/h?
Different audiences. Research instruments and WMO code forms record wind in metres per second (knots in some countries), because m/s drops straight into SI expressions for drag, energy flux, or turbine power without stray factors. Public bulletins and traffic law prefer km/h, since human journeys get counted in kilometres and hours. Identical wind, two vocabularies.
What is 10 m/s in miles per hour or knots?
10 m/s equals 22.369 mph or 19.438 knots, against 36 km/h. Those factors stay exact at source too: a statute mile measures 1609.344 metres, a nautical mile 1852 metres, so both conversions follow one pattern — multiply by 3600, then divide by 1609.344 or by 1852. Mistaking knots for kilometres per hour is endemic in sailing forecasts, where 36, 22 and 19 all describe one identical breeze.
Can I do this conversion mentally?
Yes — split 3.6 into 3 plus 0.6. Take 15 m/s: 15 × 3 = 45, then 15 × 0.6 = 9, giving 54 km/h. Another route doubles your figure, then adds 80% of that double, since 2 + 1.6 = 3.6. Field forecasters and cycling coaches mostly skip arithmetic altogether, memorising anchors instead: 5 m/s is 18 km/h, 10 is 36, 25 is 90.