Convert speed between km/h, mph, m/s, ft/s and knots — with exact conversion factors.
What Is a Speed Converter?
A speed converter translates velocity between the world’s road and science units: 100 km/h = 62.1371 mph = 27.7778 m/s. The mile is defined as exactly 1.609344 km, the knot as exactly 1.852 km/h (one nautical mile per hour — a nautical mile is one minute of latitude). Scientists use m/s because it plugs directly into physics equations; drivers use km/h or mph; sailors and pilots use knots.
How to Use
- Enter the value.
- Pick the “from” unit.
- Pick the “to” unit.
- Click “Convert Speed”.
Formula
Convert to km/h first (value × from-factor), then divide by the to-factor. All factors are exact definitions.
Worked Example
100 km/h → mph: 100 ÷ 1.609344 = 62.1371 mph. 100 km/h → m/s: 100 ÷ 3.6 = 27.7778 m/s.
How It Works, In Plain Words
Every conversion here takes the same two-step detour through km/h, which keeps all five units consistent with each other. Each unit carries an exact factor — how many km/h one of it equals: mph is 1.609344, m/s is 3.6, ft/s is 1.09728 and a knot is 1.852, while km/h itself is simply 1. Step one multiplies your value by its unit’s factor to get km/h. Step two divides that by the target unit’s factor. The worked example shows both steps compressed: 100 km/h ÷ 1.609344 = 62.1371 mph, and ÷ 3.6 = 27.7778 m/s.
Because the factors are definitions rather than measurements, they never drift: a mile is exactly 1.609344 km by international agreement, and a knot is exactly 1.852 km/h. The result is shown to as many as four decimal places, which matters more than it sounds — chained conversions and physics work both suffer when early rounding quietly eats the precision, and an exact factor deserves an exact-looking answer.
Real-World Uses
A driver crossing into a country whose signs and limits use the other system converts before judging the speedometer: knowing the limit sign’s 100 means 62.1371 mph keeps a hire car legal abroad. A sailor or pilot reads forecasts and instruments in knots and uses the tool to brief passengers or crew in the km/h they think in — remembering from this page that a knot, at 1.15 mph, is not quite the mph it resembles. And a physics student moves experimental results into m/s so the numbers plug straight into equations, converting a road-speed figure like 100 km/h into 27.7778 m/s without a factor hunt through a textbook.
Benefits
- Five units including knots for aviation and sailing
- Exact defined factors
- Both directions in one tool
- Driving, sport and science friendly
Features of Our Tool
- Instant results in your browser
- No sign-up, no download, 100% free
- Works on mobile, tablet and desktop
- Clear step-by-step explanation below the tool
- Private — your entries never leave your device
Common Mistakes
- Dividing instead of multiplying: km/h to m/s divides by 3.6; m/s to km/h multiplies
- Confusing knots with mph — a knot is 1.15 mph
- Using “kph” informally — the tool uses the standard km/h
Common Mistakes to Avoid
Direction is the classic slip: as the mistakes list warns, km/h to m/s divides by 3.6 while m/s to km/h multiplies, and doing it backwards gives an answer that looks plausible until someone checks it against a real journey. Knots cause the second trap — at 1.15 mph a knot is close enough to mph to be misread, yet different enough to matter on a chart or in a forecast. Writing “kph” informally invites the same confusion, which is why the tool sticks to the standard km/h. Finally, resist rounding mid-calculation: the factors here are exact and the display keeps four decimal places, so let the tool finish before you round for everyday use.
FAQ
How many mph is 100 km/h?
62.1371 mph.
How many m/s is 100 km/h?
27.7778 m/s.
What is a knot in km/h?
Exactly 1.852 km/h.
How do I convert mph to km/h?
Multiply by 1.609344.
Why do scientists use m/s?
Because metres and seconds are SI base units, so m/s plugs directly into physics equations without conversion factors.
Is a knot the same as a nautical mile?
Nearly — a knot is a speed, one nautical mile per hour, while the nautical mile is the distance itself. That is why this page defines the knot as exactly 1.852 km/h, and a nautical mile as one minute of latitude.
Why does the result show up to four decimal places?
Because the factors are exact, the answer can be too: 100 km/h is 62.1371 mph, not a rounded 62. For everyday use you can round the result yourself, but keeping four places stops chained conversions and science work from accumulating rounding error.