About the Speed Converter

The speed converter translates between metres per second, kilometres per hour, miles per hour, feet per second, and knots. Whether you are reading a European speed limit in km/h, an American one in mph, a maritime or aviation figure in knots, or a physics calculation in m/s, this tool gives you an instant conversion in either direction.

Metres per second is the SI unit of speed, used in scientific and engineering work. Kilometres per hour is the everyday unit in most of the world, used for road speed limits and vehicle speedometers. Miles per hour is used in the United States and the United Kingdom for the same purposes. Feet per second is used in some engineering contexts, particularly in ballistics and fluid dynamics. The knot, equal to one nautical mile per hour, is used in aviation and maritime navigation.

Every conversion is computed by first converting to metres per second (the SI base unit) and then converting to the target unit. This two-step approach through a common base unit is exact and avoids the accumulation of rounding errors that can occur when chaining direct conversions.

How It Works

Each unit has a defined relationship to metres per second, the SI unit of speed. The converter uses these factors to translate between any two units:

1 m/s   = 1 m/s
1 km/h  = 0.27777... m/s    (1/3.6)
1 mph   = 0.44704 m/s       (exact)
1 fps   = 0.3048 m/s        (exact, 1 foot per second)
1 knot  = 0.51444... m/s    (1852 metres per hour)

The conversion proceeds in two steps: the input is multiplied by the source unit's factor to give a speed in metres per second, then divided by the target unit's factor to give the result in the target unit. This is mathematically equivalent to multiplying by the ratio of the two factors.

The factor for kilometres per hour is 1/3.6 because one kilometre is 1000 metres and one hour is 3600 seconds, so 1 km/h = 1000/3600 m/s = 1/3.6 m/s. The factor for miles per hour uses the exact definition of the mile (1609.344 metres), giving 1609.344/3600 = 0.44704 m/s. The knot uses the nautical mile (1852 metres), giving 1852/3600 = 0.51444 m/s.

Worked Examples

To convert 100 km/h to mph, the calculation is (100 * 0.27778) / 0.44704 = 27.778 / 0.44704 = 62.14 mph. This is a typical highway speed limit, and the rough conversion factor of 0.621 (km/h to mph) is often memorised by drivers.

To convert 60 mph to m/s, the calculation is 60 * 0.44704 = 26.82 m/s. This is a common reference speed in physics problems, since 60 mph is approximately 27 m/s.

To convert 30 knots to km/h, the calculation is (30 * 0.51444) / 0.27778 = 15.43 / 0.27778 = 55.56 km/h. This is a typical aircraft approach speed or a fast boat speed, and the conversion factor of approximately 1.852 (knots to km/h) is widely used in aviation.

When to Use This Tool

Use the speed converter whenever you need to translate between speed units:

Reading speed limits in a foreign country (km/h vs mph).
Interpreting aircraft or boat speeds reported in knots.
Converting running, cycling, or driving speeds for fitness tracking.
Working with physics problems that use metres per second.
Comparing the top speeds of vehicles reported in different units.
Converting wind speed readings between meteorological units.
Teaching the relationships between metric and imperial speed units.

Limitations & Disclaimer

This converter handles linear speed only and does not convert Mach numbers (which depend on the speed of sound at a given altitude and temperature), acceleration units, or rotational speed (RPM). Very high speeds approaching the speed of light require relativistic treatment not provided here. For aerospace or ballistic work, use dedicated software. See our disclaimer for full details.

Frequently Asked Questions

What is a knot and why is it used in aviation and maritime navigation?

A knot is one nautical mile per hour, approximately 1.852 km/h or 1.151 mph. It is used in aviation and maritime navigation because the nautical mile corresponds to one minute of latitude, so speed in knots relates directly to the angular coordinate system of the Earth and makes navigation calculations simpler.

Why is 1 km/h equal to 1/3.6 m/s?

Because one kilometre is 1000 metres and one hour is 3600 seconds, so 1 km/h equals 1000 metres divided by 3600 seconds, which is 1/3.6 or approximately 0.2778 metres per second. The factor 3.6 is widely used to convert between km/h and m/s.

What is the difference between miles per hour and metres per second?

Miles per hour is an imperial unit used for road speeds in the United States and the United Kingdom. Metres per second is the SI unit used in scientific and engineering work. The two are related by the exact factor 0.44704, so 1 mph equals approximately 0.447 m/s and 1 m/s equals approximately 2.237 mph.

How accurate are the conversions?

The conversion factors are exact by international agreement, since they are derived from the exact definitions of the metre, the mile, and the nautical mile. The only source of error is floating-point rounding, which is negligible for any practical purpose. The converter displays up to eight decimal places.

Why does the converter go through metres per second?

To avoid accumulating rounding errors and to make the conversion logic easy to verify. Every conversion is computed as input times source factor, divided by target factor, all in exact arithmetic. Going through a common base unit is the standard approach in unit conversion libraries.

What is feet per second used for?

Feet per second is used in some engineering contexts, particularly in ballistics (where bullet speeds are often quoted in fps), fluid dynamics, and impact testing. It is also used in some American building codes for elevator and escalator speeds. The factor 0.3048 is exact because the foot is defined as exactly 0.3048 metres.

Last updated: July 21, 2026 · Author: HT99 Tools Editorial Team · Reviewed by: HT99 Tools Editorial Team