1
Unit Conversions
Speed Converter — mph, km/h, m/s, ft/s & Knots
Switch mph to km/h and back, plus m/s, ft/s and knots, using exact international factors
Speed is the conversion Americans run into the second they leave the country: a rental car's dashboard reads in kilometers per hour (km/h), the speed-limit sign says 100, and your instinct trained on miles per hour (mph) has no idea whether that's fast or slow. This converter moves any value between the five units you actually meet — mph, km/h, meters per second (m/s), feet per second (ft/s) and knots (kn) — using the exact international factors, not the back-of-the-envelope roundings.
The headline pair is mph ↔ km/h, and the one number worth memorizing is 1 mph = 1.609344 km/h exactly (the same factor that turns miles into kilometers). So that 100 km/h sign is 100 ÷ 1.609344 = 62.14 mph — a normal highway speed, not a racetrack. Going the other way, a 70 mph interstate limit is 70 × 1.609344 = 112.65 km/h.
The method is simple and exact: every speed is first converted to a single base — meters per second (m/s) — and then out to the target unit. The exact factors (m/s per unit) are:
- m/s = 1
- km/h = 1 ÷ 3.6 = 0.277777778
- mph = 0.44704 (because 1 mile = 1609.344 m and 1 hour = 3600 s)
- knot = 1852 ÷ 3600 = 0.514444444 (a knot is one nautical mile of 1852 m per hour)
- ft/s = 0.3048
Worked example — convert 60 mph to km/h. First to m/s: 60 × 0.44704 = 26.8224 m/s. Then m/s to km/h: 26.8224 ÷ 0.277777778 = 96.56 km/h. Sanity check the direct way: 60 × 1.609344 = 96.56 km/h. Both routes agree.
The m/s unit is the physics-class workhorse — gravity is 9.8 m/s², projectile and free-fall problems are all in m/s — while ft/s shows up in US ballistics and engineering, and knots rule aviation and sailing (1 knot ≈ 1.151 mph). The classic mistake is leaning on the lazy "× 1.6" rule; over a long autobahn stretch or a flight plan, the gap between 1.6 and the exact 1.609344 turns into real error. This tool uses the exact constants, so pick a value, a from unit and a to unit, and you'll also get a quick table showing the same speed in every unit at once.
Calculator
Fill in the fields and click "Calculate" for instant results.
📰 Formula
• Convert to meters per second: m/s = value × (factor of the FROM unit) • Convert out: result = m/s ÷ (factor of the TO unit) • m/s = 1 • km/h = 0.277777778 (1/3.6) • mph = 0.44704 • knot = 0.514444444 (1852/3600) • ft/s = 0.3048 • Direct headline bridge: 1 mph = 1.609344 km/h exactly
📰 Formula
• Convert to meters per second: m/s = value × (factor of the FROM unit) • Convert out: result = m/s ÷ (factor of the TO unit) • m/s = 1 • km/h = 0.277777778 (1/3.6) • mph = 0.44704 • knot = 0.514444444 (1852/3600) • ft/s = 0.3048 • Direct headline bridge: 1 mph = 1.609344 km/h exactly
🧪 Worked examples
2
Example 2
3
Example 3
4
Example 4
⚠️ Common mistakes
- Using the rough '× 1.6' rule instead of the exact 1.609344 for mph ↔ km/h.
- Confusing knots with km/h — a knot is 1.852 km/h (≈ 1.151 mph), not 1 km/h.
- Mixing up m/s and ft/s; 1 m/s is 3.281 ft/s, so the value is over 3× different.
- Dividing when you should multiply (or vice versa) between mph and km/h, flipping the answer.
- Forgetting that a 'mile per hour' uses the statute mile, while a knot uses the longer nautical mile.
💡 Tips
- Memorize one exact bridge — 1 mph = 1.609344 km/h — and the headline conversion is locked in.
- Convert through meters per second as a single base; it removes guesswork between any two units.
- For a quick gut check: km/h ÷ 1.6 ≈ mph, m/s × 2.24 ≈ mph, and 1 knot ≈ 1.15 mph.
- A 100 km/h limit is about 62 mph and a 50 km/h city limit is about 31 mph — handy when driving abroad.
Embed this calculator on your site
Copy the code below and paste it into the HTML of your site or blog.
<iframe src="https://www.calcnimbus.com/embed/speed-converter" width="100%" height="500" frameborder="0" style="border:1px solid #eee;border-radius:12px"></iframe>
❓ Frequently asked questions
How do I convert mph to km/h?
Multiply miles per hour by 1.609344. Example: 60 mph × 1.609344 = 96.56 km/h. To go the other way, divide km/h by 1.609344.
How fast is 100 km/h in mph?
100 km/h ÷ 1.609344 = 62.14 mph. That's a typical highway cruising speed, which is why many countries set rural limits near 100 km/h.
How fast is 70 mph in km/h?
70 mph × 1.609344 = 112.65 km/h. A US interstate limit of 70 mph is just under 113 km/h, close to the 110–120 km/h limits common in Europe.
What is a knot and how does it compare to mph?
A knot is one nautical mile (1,852 m) per hour. That makes 1 knot equal to 1.852 km/h or about 1.151 mph, so 20 knots is roughly 23 mph.
How do I convert m/s to mph?
Multiply meters per second by 2.2369 (or convert exactly: m/s × 3.6 gives km/h, then divide by 1.609344). For example, 10 m/s = 22.37 mph.
How do I convert m/s to km/h?
Multiply meters per second by 3.6, since 1 m/s = 3.6 km/h exactly. So 25 m/s × 3.6 = 90 km/h, a common highway speed.
What is the difference between m/s and ft/s?
They both measure distance per second but in different units: 1 m/s = 3.28084 ft/s. So a 30 m/s wind is about 98.4 ft/s — easy to mix up if you ignore the unit.
Are these speed conversion factors exact or approximate?
They're exact. The mile is defined as 1,609.344 m, the foot as 0.3048 m and the nautical mile as 1,852 m by international agreement, so this converter gives official results, not roundings.
How do I convert km/h to mph in my head?
Divide kilometers per hour by about 1.6 for a quick estimate, or multiply by 0.62. So 100 km/h is roughly 62 mph and 50 km/h is about 31 mph.