How to Convert km/h to mph (and mph to km/h)
Divide km/h by 1.609344 to get mph (100 km/h = 62.14 mph); multiply mph by 1.609344 for km/h. Mental shortcut, table, Indian speed limits and m/s.
To convert km/h to mph, divide by 1.609344 (or multiply by about 0.621371). To convert mph to km/h, multiply by 1.609344. So 100 km/h is 62.14 mph, and 60 mph is 96.56 km/h. For a rough answer in your head, multiply km/h by 5 and divide by 8.
The free speed converter does all four common units at once: km/h, mph, metres per second and knots. Below are the exact factor, two mental shortcuts, a quick-reference table, India's legal speed limits in both units, and the m/s conversion physics students need.
The exact factor and why it is exact
Since 1959 the international mile has been defined as exactly 1,609.344 metres (1,760 yards of 0.9144 m each). So 1 mile per hour is exactly 1.609344 km/h, with no rounding. Going the other way, 1 km/h = 1 ÷ 1.609344 = 0.621371 mph, rounded to six decimal places.
Worked example 1: 80 km/h to mph. 80 ÷ 1.609344 = 49.709695, so about 49.71 mph. The speed converter shows 49.709695 mph.
Worked example 2: 70 mph to km/h. 70 × 1.609344 = 112.65408 km/h, about 112.65 km/h. That is the top limit on UK motorways.
Using the speed converter: type the number in Value, choose From and To (To starts on knot, so switch it to mph) and press Convert. The big result shows the answer to six decimal places, and the rows below show the same speed in every other unit, so one entry gives you mph, m/s and knots together.
Mental shortcuts
- km/h to mph: × 5 ÷ 8. 120 km/h ÷ 8 = 15, × 5 = 75 mph. The exact answer is 74.56, so this is 0.6% high.
- km/h to mph, faster but rougher: × 0.6. 100 km/h ≈ 60 mph (exact 62.14, so 3.4% low). Fine for a glance at a sign.
- mph to km/h: × 8 ÷ 5, which is × 1.6. 60 mph × 1.6 = 96 km/h (exact 96.56).
- The Fibonacci trick: neighbouring numbers in 5, 8, 13, 21, 34, 55, 89 are close to a mile-to-kilometre pair. 55 mph ≈ 89 km/h (exact 88.51).
Quick-reference table
| km/h | mph | mph | km/h |
|---|---|---|---|
| 20 | 12.43 | 20 | 32.19 |
| 30 | 18.64 | 30 | 48.28 |
| 40 | 24.85 | 40 | 64.37 |
| 50 | 31.07 | 50 | 80.47 |
| 60 | 37.28 | 60 | 96.56 |
| 70 | 43.50 | 70 | 112.65 |
| 80 | 49.71 | 80 | 128.75 |
| 100 | 62.14 | – | – |
| 120 | 74.56 | – | – |
| 140 | 86.99 | – | – |
Speed limits in India, in km/h and mph
The Ministry of Road Transport and Highways set the national maximum speeds in notification S.O. 1522(E) of 6 April 2018:
| Vehicle | Expressway (access-controlled) | 4-lane or wider, divided | Within municipal limits | Other roads |
|---|---|---|---|---|
| Cars and other passenger vehicles with up to 8 seats besides the driver (M1) | 120 | 100 | 70 | 70 |
| Buses with 9 or more seats (M2, M3) | 100 | 90 | 60 | 60 |
| Goods vehicles (N) | 80 | 80 | 60 | 60 |
| Motorcycles | 80 (if allowed on the expressway) | 80 | 60 | 60 |
| Three-wheelers | – | 50 | 50 | 50 |
All figures are km/h. For a car, 120 km/h is 74.56 mph, 100 km/h is 62.14 mph and 70 km/h is 43.50 mph. These are the highest limits the law allows. State governments and local authorities can set lower limits for a stretch of road and put up signs, and the posted sign is the limit you must follow.
Driving abroad works the other way round. In the UK the national limits for cars are 30 mph in built-up areas (20 mph in Wales), 60 mph on single carriageways and 70 mph on dual carriageways and motorways. That is 48.28, 96.56 and 112.65 km/h. A rented car there shows mph on the main dial.
km/h to m/s, for physics problems
Physics uses metres per second. One kilometre is 1,000 m and one hour is 3,600 s, so:
- km/h to m/s: divide by 3.6. 72 km/h ÷ 3.6 = 20 m/s.
- m/s to km/h: multiply by 3.6. 15 m/s × 3.6 = 54 km/h.
- mph to m/s: multiply by 0.44704 (exact). 30 mph = 13.4112 m/s.
Worked example 3. A bus covers 180 km in 2.5 hours. The speed, distance and time calculator gives an average of 72 km/h. In physics units that is 72 ÷ 3.6 = 20 m/s, and for a friend in the US it is 72 ÷ 1.609344 = 44.74 mph. At 20 m/s the bus travels 40 m in the 2 seconds a driver might take to react.
The usual exam slip is dividing when you should multiply. A quick check: a speed in m/s is always the smaller number, because a metre per second is a faster unit than a kilometre per hour.
Knots, briefly
Ships and aircraft use knots: one nautical mile per hour, where a nautical mile is exactly 1,852 m. So 1 knot = 1.852 km/h ≈ 1.15 mph. Wind speeds in marine and aviation weather reports are also often in knots: 30 knots is 55.56 km/h or 34.52 mph.
Common mistakes
- Using 1.6 where precision matters. For a sign it is fine; for a spec sheet or an exam answer, use 1.609344.
- Rounding too early. Convert first, then round. The converter's six decimals (120 km/h = 74.564543 mph) are more than you need; 74.6 mph is plenty.
- Mixing distance and speed. The factor is the same, but if you only need distances, the length converter handles kilometres, miles, metres and feet.
For all the everyday conversions on one page, see the unit conversion cheat sheet. Planning a long drive? The fuel cost guide works out what the trip will cost.
Frequently asked questions
What is 100 km/h in mph?
62.14 mph (100 ÷ 1.609344). The quick estimate is 60.
What is 120 km/h in mph?
74.56 mph. That is the top speed for cars on access-controlled expressways in India.
How do I convert mph to km/h?
Multiply by 1.609344, or by 1.6 for a rough answer. 50 mph = 80.47 km/h.
What is the speed limit on Indian highways?
For cars, the national maximum is 100 km/h on four-lane divided highways and 120 km/h on access-controlled expressways, under the 2018 notification. Posted signs can set lower limits, and those apply.
How do I convert km/h to m/s?
Divide by 3.6. 90 km/h = 25 m/s.
Sources: Ministry of Road Transport and Highways notification S.O. 1522(E), 6 April 2018 (maximum speeds); GOV.UK, "Speed limits"; International Yard and Pound Agreement, 1959 (definition of the mile); the international nautical mile of 1,852 m.
- #km/h to mph
- #mph to km/h
- #speed conversion
- #indian speed limits
- #km/h to m/s
- #knots