On this page
Formula
Target speed = Speed × (m/s per source unit ÷ m/s per target unit)
- Speed
- the value you type in
- m/s per unit
- each unit's exact size in meters per second (1 mph = 0.44704, 1 km/h = 1/3.6, 1 ft/s = 0.3048, 1 knot = 1,852/3,600)
- Target speed
- the same speed in the unit you convert to
What the speed converter does
Speed is distance divided by time, so every speed unit pairs a length unit with a time unit. This speed converter handles the five that cover nearly every everyday and technical use:
- Miles per hour (mph): road speeds in the US and UK.
- Kilometers per hour (km/h): road speeds almost everywhere else, and wind speeds in most weather services.
- Meters per second (m/s): the SI unit, used in physics, engineering and many wind reports.
- Feet per second (ft/s): ballistics, fluid flow and US engineering.
- Knots (kn): nautical miles per hour, the standard at sea and in aviation.
Enter a speed, pick the units, and the result appears with the multiplier used. The table under it lists the same speed in all five units.
Using the speed converter
Type the speed into Value, then choose the unit it is measured in and the one you want. There is no Convert button: the answer refreshes with every keystroke, so you can try 60, 65 and 70 mph in a few seconds. The working line spells out the multiplier, and the result table lets you read knots, m/s and ft/s without changing the dropdowns. Share creates a link that reopens the page with the same speed and units, which is useful for sending a wind reading or a speed limit to someone else.
Speed converter formula: converting by hand
Because each unit is a fixed number of meters per second, any conversion is a multiply and a divide. Here is 70 mph to km/h:
- 1 mph is exactly 0.44704 m/s, and 1 km/h is 1/3.6 m/s.
- The ratio is 0.44704 × 3.6 = 1.609344, the number of kilometers in a mile.
- 70 × 1.609344 = 112.65 km/h.
When only the distance unit changes (miles to kilometers), the speed factor equals the length factor. When the time unit changes too, as with m/s to km/h, multiply by the ratio of the time units: 3,600 seconds per hour ÷ 1,000 meters per kilometer = 3.6.
Speed converter chart: conversion factors
| From | To | Multiply by |
|---|---|---|
| mph | km/h | 1.609344 |
| km/h | mph | 0.621371 |
| m/s | km/h | 3.6 |
| km/h | m/s | 0.277778 |
| mph | m/s | 0.44704 |
| m/s | mph | 2.236936 |
| mph | ft/s | 1.466667 |
| knots | mph | 1.150779 |
| knots | km/h | 1.852 |
| mph | knots | 0.868976 |
Factors were computed with the converter’s exact definitions and rounded to six decimals.
Common speeds in each unit
| Example | mph | km/h | m/s | knots |
|---|---|---|---|---|
| Walking pace | 3 | 4.83 | 1.34 | 2.61 |
| School zone limit | 20 | 32.19 | 8.94 | 17.38 |
| Urban speed limit | 35 | 56.33 | 15.65 | 30.41 |
| US interstate limit | 70 | 112.65 | 31.29 | 60.83 |
| Hurricane threshold (Category 1) | 74 | 119.09 | 33.08 | 64.3 |
| Usain Bolt’s 100 m average | 23.35 | 37.58 | 10.44 | 20.29 |
| Commercial jet cruise | 575 | 925.37 | 257.05 | 499.66 |
Where each unit is used
- Driving. Speedometers sold in the US show mph with a smaller km/h scale. Rental cars abroad and road signs in Canada and Mexico use km/h, so knowing that 100 km/h is about 62 mph helps you keep to the limit.
- Weather. The National Weather Service reports wind in mph for the public and in knots for marine and aviation forecasts. A hurricane begins at 74 mph, or 64 knots.
- Science and engineering. Physics formulas use m/s so that energy and force come out in joules and newtons. The velocity calculator works in those units.
- Sailing and flying. Knots pair with nautical miles on charts: a boat making 6 knots covers 6 nautical miles in an hour.
- Running and cycling. Athletes think in pace (minutes per mile or kilometer) rather than speed. The pace calculator converts between the two.
Common mistakes
- Using 1.6 for precise work. It is fine for road signs but 0.6% low; over a 300-mile trip that is almost 3 km.
- Treating knots as mph. A 25-knot boat is doing about 28.8 mph, not 25.
- Mixing up per hour and per second. 10 m/s is 36 km/h, not 10 km/h. When converting by hand, track both the distance and the time unit.
- Expecting Mach to be fixed. Mach 1 is about 761 mph at sea level on a 59 °F day but only about 660 mph at airliner altitude, because sound travels slower in cold air.
A note on Mach numbers
Mach number is a ratio, not a fixed unit: it is an object’s speed divided by the speed of sound in the air around it. Because sound travels faster in warm air, Mach 1 is about 340 m/s near the ground on a mild day but about 295 m/s at airliner cruising altitude, where the air is around −55 °C. To express a speed as a Mach number, convert it to m/s here, then divide by the speed of sound for the temperature you care about.
Glossary
- Knot: one nautical mile (1,852 m) per hour.
- Ground speed vs airspeed: an aircraft’s speed over the ground differs from its speed through the air by the wind component.
- Average speed: total distance divided by total time, which can differ from the speed shown at any moment.
Worked examples
Highway speed limit in km/h
Convert a 65 mph speed limit to kilometers per hour.
Inputs: Value = 65; From = Miles per hour (mph); To = Kilometers per hour (km/h)
65 mph × 1.609344 = 104.60736 km/h
Answer: 65 mph = 104.60736 km/h
Boat speed in mph
A boat cruising at 30 knots, in miles per hour.
Inputs: Value = 30; From = Knots (kn); To = Miles per hour (mph)
30 kn × 1.150779448 = 34.523383 mph
Answer: 30 kn = 34.523383 mph
Meters per second to km/h (edge case)
One meter per second is exactly 3.6 km/h, the factor behind every m/s conversion.
Inputs: Value = 1; From = Meters per second (m/s); To = Kilometers per hour (km/h)
1 m/s × 3.6 = 3.6 km/h
Answer: 1 m/s = 3.6 km/h
Jogging pace in feet per second
A 10 km/h jog in feet per second.
Inputs: Value = 10; From = Kilometers per hour (km/h); To = Feet per second (ft/s)
10 km/h × 0.9113444153 = 9.113444 ft/s
Answer: 10 km/h = 9.113444 ft/s
Assumptions and limitations
- Every factor is exact. A mile is 1,609.344 m and a nautical mile 1,852 m, so 1 mph = 0.44704 m/s and 1 knot = 0.514444 m/s.
- Mach number is not included, because the speed of sound depends on air temperature (about 343 m/s at 20 °C, lower at altitude). Convert to m/s and divide by the local speed of sound if you need it.
- The converter changes units of an average or instantaneous speed. It does not turn running pace (minutes per mile) into speed; use the pace calculator for that.
- Results show up to 6 decimal places and speeds can't be negative.
Frequently asked questions
How do you convert mph to km/h?
Multiply by 1.609344. 55 mph is 55 × 1.609344 = 88.5 km/h. For a quick estimate, multiply by 1.6, or add 60% to the mph figure.
How do you convert km/h to mph?
Multiply by 0.621371, or divide by 1.609344. A 120 km/h motorway limit is 74.6 mph. A rough rule is to multiply by 6 and drop the last digit, so 120 becomes 72.
How do you convert meters per second to km/h?
Multiply by 3.6, because an hour has 3,600 seconds and a kilometer 1,000 meters. 20 m/s is 72 km/h, and dividing by 3.6 goes back.
What is a knot in mph?
One knot is one nautical mile per hour, 1.15078 mph or 1.852 km/h. A 15-knot wind is about 17.3 mph.
Why does 60 mph equal 88 feet per second?
60 mph is one mile per minute, or 5,280 ft per 60 s, which is 88 ft/s. It is a handy check that a car covers about 88 ft every second at highway speed.
Is speed the same as velocity?
Speed is how fast something moves. Velocity is speed plus direction. The units are the same, so this converter works for either. To work velocity out from distance and time, use the [velocity calculator](/velocity-calculator/).
Sources
- NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically — National Institute of Standards and Technology (NIST). Checked October 12, 2026.
- SI Units – Length — National Institute of Standards and Technology (NIST). Checked October 12, 2026.
- The International System of Units (SI Brochure) — Bureau International des Poids et Mesures (BIPM). Checked October 12, 2026.