🔁 Conversion
Converting mph to km/h (and Back Again)
The simple factor for turning miles per hour into kilometres per hour, quick mental shortcuts, and how mph, km/h, m/s and knots relate.
Updated 28 September 2026 · 2 min read
Cross a border, read a foreign spec sheet or watch an overseas weather report and you'll hit two different speed units: miles per hour (mph), used mainly in the UK and US, and kilometres per hour (km/h), used almost everywhere else. Converting between them is a single multiplication.
The exact conversion
So 60 mph is 60 × 1.60934 ≈ 96.6 km/h, and a 100 km/h motorway limit is 100 ÷ 1.60934 ≈ 62.1 mph. The speed converter does this instantly and shows the result in every other common unit at the same time.
Mental shortcuts
You rarely need three decimal places at the roadside. Two shortcuts get you close:
- mph → km/h: add roughly 60%. Take the mph figure, halve it, add that half plus a touch. 70 mph → 70 + 35 + a bit ≈ 112 km/h (exact: 112.7).
- km/h → mph: multiply by 0.62, or take five-eighths. 120 km/h → 120 × 0.62 ≈ 74 mph (exact: 74.6).
A handy landmark: 50 mph ≈ 80 km/h almost exactly, and it climbs neatly from there — 60 mph ≈ 97 km/h, 70 mph ≈ 113 km/h.
The other speed units
Two more units turn up often enough to know:
- Metres per second (m/s) is the scientific standard. To go from km/h to m/s, divide by 3.6; the other way, multiply by 3.6. So 36 km/h = 10 m/s.
- Knots (kn) are nautical miles per hour, used in aviation and at sea. One knot is about 1.15 mph or 1.85 km/h.
Why the factor is what it is
Every speed unit is just a distance over a time. Because 'per hour' is common to both mph and km/h, converting the speeds is the same as converting the distances: miles to kilometres. That's why the 1.60934 factor for length does double duty here. The same logic underlies our wider look at metric versus imperial units, and if it's height rather than speed you're juggling, see converting height from cm to feet.
When you'd rather not do the arithmetic, the converter below handles mph, km/h, m/s, ft/s and knots in any direction.
Frequently asked questions
- Is 1 mph exactly 1.6 km/h?
- Almost — the precise factor is 1.60934. Using 1.6 is fine for a rough head estimate, but it drifts by about 0.6% and the error grows at higher speeds, so use the full figure when accuracy matters.
- How do I convert km/h to m/s quickly?
- Divide by 3.6. It works because there are 3,600 seconds in an hour and 1,000 metres in a kilometre, and 3,600 ÷ 1,000 = 3.6. So 90 km/h ÷ 3.6 = 25 m/s.