What is mile per hour?

Mile per hour is a unit of speed equal to one mile travelled in one hour. It is the standard unit for road speeds, vehicle performance ratings, and weather reports in the United States and United Kingdom.

Real-world uses

Miles per hour is the standard speed unit for road traffic in the United States, the United Kingdom, and a few other countries. Baseball pitching speed, hurricane wind categories (Saffir-Simpson scale), and NASCAR race speeds are quoted in mph.

History

Miles per hour became the standard speed expression in English-speaking countries with the advent of railways and later automobiles. The first US speed limit (8 mph in New York City, 1901) and British speed cameras use mph as the legal standard.

Common mistakes

Assuming mph-to-km/h conversion is a simple ×1.5—the actual factor is 1.609. Also, forgetting that UK and US speed limits both use mph, which can mislead visitors from metric countries into driving too fast or too slow.

What is knot?

A knot is a unit of speed equal to one nautical mile per hour, approximately 1.852 km/h. It is the international standard for maritime navigation, aviation, and meteorological wind speed reporting.

Real-world uses

Knots are the universal speed unit in maritime navigation and aviation worldwide, regardless of whether a country uses metric or imperial. Ship speeds, ocean currents, wind speed in aviation weather (METAR) reports, and jet stream velocities are all given in knots.

History

The knot originates from the 17th-century practice of measuring ship speed by throwing a log overboard attached to a rope with knots tied at regular intervals. Sailors counted how many knots paid out in a fixed time (measured by a sandglass).

Common mistakes

Saying "knots per hour"—a knot already means nautical miles per hour, so adding "per hour" is redundant and incorrect. Also, confusing knots with km/h: 1 knot ≈ 1.852 km/h.

When is this conversion used?

Speed limits, vehicle speedometers, and weather reports for wind speeds use different units depending on the country, making km/h to mph conversion one of the most practical speed conversions.

Worked examples

1 mile per hour = 0.86897624 knot

1 knot = 0.51444444 metre per second

How to convert mile per hour to knot

To convert mile per hour to knot, multiply the value by 0.86897624.

To convert knot back to mile per hour, multiply by 1.15077945.

Measurement standards

The SI unit of speed is metres per second (m/s), a derived unit requiring no independent definition. The knot is defined as exactly one nautical mile (1,852 metres) per hour and is sanctioned for maritime and aeronautical navigation by the International Civil Aviation Organization.

Did you know?

The fastest human-made object is the Parker Solar Probe, which reached 635,266 km/h (about 176 km/s) in 2024 during a close pass of the Sun — fast enough to travel from New York to Tokyo in under a minute.

Quick reference: mile per hour to knot

Common values

Available Speed units

• metre per second conversions
• kilometre per hour conversions
• mile per hour conversions
• knot conversions
• foot per second conversions
• metre per minute conversions
• kilometre per second conversions
• mach (approx at sea level) conversions
• centimetre per second conversions
• mile per minute conversions

More mile per hour conversions

• Convert mile per hour to metre per second
• Convert mile per hour to kilometre per hour
• Convert mile per hour to knot
• Convert mile per hour to foot per second
• Convert mile per hour to metre per minute
• Convert mile per hour to kilometre per second
• Convert mile per hour to mach (approx at sea level)
• Convert mile per hour to centimetre per second
• Convert mile per hour to mile per minute

Assumption: Mach uses an approximate sea-level reference (about 340.29 m/s).