One knot = 1 nautical mile per hour = 1.852 km/h = 0.5144 m/s. The name comes from measuring speed by counting knots on a rope thrown from the boat: each knot passed with time. The standard is still used in maritime and aviation because it maps directly to latitude (one knot = one arc-minute per hour).

Mach 1 is the local speed of sound in the medium. In air at sea level and 15°C it’s about 340.3 m/s or 1225 km/h. The value drops with temperature: at 11,000 m altitude (−56.5°C) the speed of sound is only about 295 m/s. Mach 2 is twice the local sound speed regardless of altitude. The unit is named after physicist Ernst Mach.

Why do sailing and aviation use knots?

Because navigation uses latitude and longitude. One nautical mile is one arc-minute along the meridian, so one knot is one arc-minute per hour. This makes position calculations with sextants, GPS and charts straightforward. Nautical miles and knots are internationally standardised by IMO and ICAO for maritime and aviation use.

Light speed in vacuum is exactly 299,792,458 m/s or 1,079,252,848.8 km/h. The value has been fixed by definition since 1983 and is used to define the metre (1 metre = distance light travels in 1/299,792,458 s). In glass and water it’s slower: light in water is about 225,000 km/s, in ordinary glass about 200,000 km/s.

Speed Converter - km/h, m/s, mph, knots & Mach

Unit	km/t	m/s	mph	knop
1 km/t	1	0.27778	0.62137	0.53996
1 m/s	3.6	1	2.23694	1.94384
1 mph	1.60934	0.44704	1	0.86898
1 knop	1.852	0.51444	1.15078	1
1 Mach	1234.8	343	767.27	666.74

Unit

km/t

m/s

mph

knop

1 km/t

0.27778

0.62137

0.53996

1 m/s

3.6

2.23694

1.94384

1 mph

1.60934

0.44704

0.86898

1 knop

1.852

0.51444

1.15078

1 Mach

1234.8

343

767.27

666.74

How speed is calculated

All speed conversions are calculated using meters per second (m/s) as the base SI unit.

Kilometer i timen (km/t): 1 m/s is exactly 3.6 km/h.
Miles per hour (mph): Based on the international mile (1609.344 meters). 1 mph is exactly 0.44704 m/s.
Knop (kn): Defined as one nautical mile (1852 meters) per hour. 1 knot is exactly 1.852 km/h, which is approximately 0.5144 m/s.
Mach: Represents the speed of sound in dry air at 20 °C at sea level, which is approximately 343 m/s (1234.8 km/h).

About this tool

The speed converter maps between km/h, m/s, mph, knots, feet per second and Mach numbers. Useful for travel (km/h ↔ mph), sports (m/s for running, knots for sailing), aviation (Mach and knots), physics problems, and reading foreign road signs. We also show the speed of light as a reference, handy for astronomy and relativity work.

How to use it

Type a value in any field.
See all other units update in real time.
Switch to the aviation tab for Mach and knots.
Copy the result with one click.

Examples

US highway

Input65 mph

Output104.6 km/h (29.06 m/s)

747 cruise speed

Input490 knop

OutputMach 0.85 (at 10 000 m altitude)

The Mach number depends on local speed of sound, which drops with temperature at altitude. At cruise altitude it’s ~295 m/s; at sea level ~343 m/s.

100-metre sprint

Input10.5 m/s

Output37.8 km/h (23.5 mph)

Common use cases

Travel: convert speed limits between Europe (km/h) and the US (mph).
Sailing and boating: knots ↔ km/h and m/s.
Running: m/s ↔ km/h for training analysis.
Aviation: Mach number, knots and feet per second.
Physics: convert to SI units (m/s).

Frequently asked questions

What is one knot?: One knot = 1 nautical mile per hour = 1.852 km/h = 0.5144 m/s. The name comes from measuring speed by counting knots on a rope thrown from the boat: each knot passed with time. The standard is still used in maritime and aviation because it maps directly to latitude (one knot = one arc-minute per hour).
What is Mach 1?: Mach 1 is the local speed of sound in the medium. In air at sea level and 15°C it’s about 340.3 m/s or 1225 km/h. The value drops with temperature: at 11,000 m altitude (−56.5°C) the speed of sound is only about 295 m/s. Mach 2 is twice the local sound speed regardless of altitude. The unit is named after physicist Ernst Mach.
Why do sailing and aviation use knots?: Because navigation uses latitude and longitude. One nautical mile is one arc-minute along the meridian, so one knot is one arc-minute per hour. This makes position calculations with sextants, GPS and charts straightforward. Nautical miles and knots are internationally standardised by IMO and ICAO for maritime and aviation use.
How fast is light?: Light speed in vacuum is exactly 299,792,458 m/s or 1,079,252,848.8 km/h. The value has been fixed by definition since 1983 and is used to define the metre (1 metre = distance light travels in 1/299,792,458 s). In glass and water it’s slower: light in water is about 225,000 km/s, in ordinary glass about 200,000 km/s.

Technical background

All speeds convert via m/s as the SI base. Constants (all exact by definition): 1 km/h = 1000/3600 m/s = 0.27778 m/s, 1 mph = 1609.344/3600 m/s = 0.44704 m/s, 1 knot = 1852/3600 m/s = 0.51444 m/s, 1 ft/s = 0.3048 m/s, speed of sound in standard atmosphere (15°C, sea level) ≈ 340.294 m/s, speed of light in vacuum = 299,792,458 m/s (exact, SI definition). Mach number is dimensionless and relative to the local sound speed, which depends on air temperature T: c = √(γ·R·T) ≈ 20.05·√T m/s with T in Kelvin, γ = 1.4 (diatomic gas), R = 287.05 J/(kg·K). The tool uses standard-atmosphere sea-level temperature unless you pick a specific altitude. All computations use JavaScript Number (IEEE 754 double), well beyond practical precision needs.

Speed Reference Table