Speed Units Converter
Convert a speed between km/h, mph, m/s, ft/s, knots and Mach instantly. Enter any value, pick the unit, and see the equivalent in all other common speed units.
Convert Speed Units
Speed Converter Formula
Where:
- \(v_{\text{source}}\) — the speed you entered, in the source unit
- \(v_{\text{target}}\) — the same speed expressed in the target unit
- \(f\) — the factor that converts a unit to meters per second (the base unit)
The converter first rewrites your input in meters per second, then divides by the target unit's factor. This two-step approach guarantees that every pair of units is converted consistently.
| Unit | Factor to m/s | Definition |
|---|---|---|
| km/h | \(1000/3600 \approx 0.277778\) | 1 kilometer per hour |
| mph | \(0.44704\) | 1 international mile (1609.344 m) per hour |
| m/s | \(1\) | SI base unit of speed |
| ft/s | \(0.3048\) | 1 foot per second |
| knots | \(1852/3600 \approx 0.514444\) | 1 nautical mile (1852 m) per hour |
| Mach | \(343\) | Speed of sound at sea level, 20 °C |
Speed Converter – Calculation Example
Example: a car travels at 100 km/h on a highway. What is that in mph, m/s, ft/s, knots and Mach?
\[ 100 \text{ km/h} \times \frac{1000}{3600} = 27.7778 \text{ m/s} \]
\[ 27.7778 \times 3.6 = 100 \text{ km/h}, \quad \frac{27.7778}{0.44704} = 62.1371 \text{ mph} \]
\[ \frac{27.7778}{0.3048} = 91.3440 \text{ ft/s}, \quad 27.7778 \times \frac{3600}{1852} = 53.9957 \text{ knots} \]
\[ \frac{27.7778}{343} = 0.0810 \text{ Mach} \]
Result: 100 km/h = 27.7778 m/s = 62.1371 mph = 91.3440 ft/s = 53.9957 knots = 0.0810 Mach.
How to Use the Speed Converter
- Enter your speed in the Speed value field (the default is 100).
- Choose the unit of that value from the Unit dropdown: km/h, mph, m/s, ft/s, knots or Mach.
- The Converted Speeds table updates instantly, showing the equivalent speed in all the other common units.
- To convert in the other direction, simply enter the new value and switch the unit — no reset needed.
What Is a Speed Unit Conversion?
Speed is distance divided by time, and the same physical speed can be written in many different units depending on where you are and what you are measuring. Road speeds are given in km/h in most of the world but in mph in the United States and the United Kingdom. Physics and engineering work almost exclusively with m/s, the SI unit. Aviation and maritime navigation use knots, because a knot is one nautical mile per hour and nautical miles map directly onto coordinates on charts.
Because all these units describe the same quantity, they are tied together by exact ratios. One mile is defined as exactly 1609.344 meters and one foot as exactly 0.3048 meters, so mph and ft/s convert to m/s with no rounding error. The knot is based on the nautical mile of exactly 1852 meters, also an exact definition.
Mach is different: it is not a fixed unit but a ratio of speed to the speed of sound. This calculator uses 343 m/s, the speed of sound in dry air at sea level and 20 °C. In real atmospheric conditions the speed of sound changes with temperature, so a Mach number is only meaningful together with those conditions. For everyday comparisons — for example, how fast a 900 km/h airliner is relative to sound — the sea-level value is a good standard reference.
Interpreting the result is straightforward: the number in each row is simply your original speed written in that unit. Nothing about the motion changes, only the measuring stick.
Assumptions, Limitations and Tips
- Mach is approximate. The conversion uses 343 m/s (sea level, 20 °C). At high altitude the speed of sound drops to roughly 295 m/s, so the same true airspeed corresponds to a higher Mach number there.
- All other factors are exact by international definition, so results are limited only by rounding to 4 decimal places.
- Negative values are rejected — speed, as opposed to velocity, has no direction and cannot be negative.
- Watch out for mixed units in real life. Car speedometers in the UK show mph while distances are in miles; weather reports in Canada give wind in km/h. A quick conversion check helps avoid mistakes.
- For reference: 100 km/h ≈ 62 mph, 60 mph ≈ 97 km/h, and 1 knot ≈ 1.151 mph ≈ 1.852 km/h.
Related Converters
If you work with speeds of downloads, our Download Time Estimator converts data-transfer rates the same way. Since ft/s is built from feet, the Meters to Feet converter handles the underlying length conversion, and the Metric Prefix converter is useful when speeds appear as mm/s or km/s. For other physical quantities, see the Pressure converter.
Frequently Asked Questions
How do I convert km/h to mph by hand?
Multiply the km/h value by 0.621371, because 1 km/h ≈ 0.621371 mph. For a quick mental estimate, multiply by 0.6 and add a little. For example, 120 km/h × 0.621371 ≈ 74.56 mph. To go the other way, multiply mph by 1.609344. A useful checkpoint: 100 km/h ≈ 62 mph and 60 mph ≈ 97 km/h.
How many km/h is 1 knot, and why is it used at sea?
One knot equals exactly 1.852 km/h or about 1.151 mph. Ships and aircraft use knots because the nautical mile is defined as exactly 1852 meters, which corresponds to one minute of latitude on navigational charts. That makes it easy to translate speed directly into distance traveled along a meridian, which statute miles or kilometers do not allow.
Why do physicists prefer m/s instead of km/h?
Meters per second is the SI base unit for speed, so it fits directly into formulas for force, kinetic energy, and momentum without extra conversion factors. For example, kinetic energy \( E = \tfrac{1}{2}mv^2 \) requires v in m/s if the mass is in kilograms and the energy is to come out in joules. Remember the simple link: 1 m/s = 3.6 km/h exactly.
How fast is Mach 1, and is it always the same speed?
Mach 1 is the speed of sound in the surrounding air. This calculator uses 343 m/s (1235 km/h, about 767 mph), which applies to dry air at sea level and 20 °C. In reality the speed of sound depends mainly on temperature: at cruise altitude of about 11,000 m it drops to roughly 295 m/s, so the same aircraft has a higher Mach number up there than at sea level.
What is a typical walking, running, or cycling speed in these units?
A brisk walk is about 5 km/h (3.1 mph, 1.4 m/s). Recreational running is around 10 km/h (6.2 mph), while elite marathon runners sustain roughly 20 km/h (12.4 mph). Casual cycling is about 15–20 km/h, and highway driving is typically 100–130 km/h (62–81 mph). Airliners cruise near 900 km/h, close to Mach 0.8.
How do I convert ft/s to mph or km/h?
One foot per second equals exactly 0.3048 m/s, which is 0.681818 mph or 1.09728 km/h. So 100 ft/s ≈ 68.2 mph. A handy shortcut: 88 ft/s is exactly 60 mph, a conversion often used in ballistics and engineering in the United States. To convert ft/s to m/s, simply multiply by 0.3048 — the foot has been defined as exactly 0.3048 meters since 1959.
Can I use this converter for wind speed and hurricane categories?
Yes. Wind speeds are reported in knots, km/h, or mph depending on the region, and this converter handles all of them. For example, a tropical storm becomes a hurricane at 64 knots (119 km/h, 74 mph). Keep in mind that official scales such as Saffir-Simpson use sustained wind speeds averaged over one minute (US practice) or ten minutes (elsewhere), so check which averaging convention applies before comparing storms.