Speed Converter: km/h, mph, m/s, Knots

Convert between metric and imperial speed units instantly. Supports kilometers per hour, miles per hour, meters per second, knots, and feet per second. Calculate trip fuel costs at any speed with our Fuel Cost Calculator, or explore all unit categories at our Unit Converter.

Visual Scale Comparison

Complete Conversion Reference

Unit Definitions

How it works

This converter uses exact mathematical ratios to translate between speed units. All conversions pass through meters per second (m/s), the SI base unit: 1 km/h = 1/3.6 m/s, 1 mph = 0.44704 m/s, 1 knot = 0.514444 m/s (one nautical mile per hour), and 1 ft/s = 0.3048 m/s. Knots are the global standard for maritime and aviation speed, while km/h and mph dominate road traffic in metric and imperial countries respectively.

Enter a value in either field and the converter instantly calculates the result. Use the swap button to reverse the conversion direction. The quick reference table and all-to-all matrix provide common values at a glance.

How Speed Conversion Works

Speed conversion translates a velocity measurement from one unit to another using fixed ratios. The SI base unit for speed is meters per second (m/s). To convert between units, values are first expressed in m/s, then converted to the target unit. Key relationships: 1 km/h equals 1/3.6 m/s, 1 mph equals 0.44704 m/s, and 1 knot equals 0.514444 m/s (one nautical mile per hour). Conversions are straightforward multiplication or division by these factors.

Common Speed Conversions

The most frequently searched speed conversions are km/h to mph (driving abroad), m/s to km/h (weather and physics), and knots to km/h or mph (marine and aviation). A quick approximation: multiply km/h by 0.6 to estimate mph, or multiply mph by 1.6 for km/h. For wind speed reports, meteorologists in Europe use km/h or m/s, while US forecasts use mph and maritime forecasts use knots worldwide.

When You Need Speed Conversion

Speed conversion is essential when traveling between countries that use different systems — European road signs show km/h while US and UK signs show mph. Sailors and pilots work in knots regardless of their home country. Scientists and engineers use m/s as the standard for physics equations. Wind speed reports vary by country and context: weather services may report in km/h, mph, m/s, or knots depending on the audience. Athletics uses m/s for sprint analysis but km/h or mph for general reporting.

Speed Units Around the World

Most countries use kilometers per hour for road speed limits and vehicle speedometers. The United States, United Kingdom, and a handful of other nations use miles per hour for road traffic. Knots are the universal standard in maritime navigation and aviation, linking speed to the nautical mile (1,852 meters). Meters per second is the scientific standard used in physics and engineering globally. Feet per second appears in some specialized fields including ballistics and American engineering standards.

Tips for Accurate Speed Conversion

Use the exact conversion factor rather than approximations for precise work. The common shortcut of "divide km/h by 1.6 for mph" introduces about 0.6 percent error compared to the exact factor of 1.60934. For knots to km/h, multiply by 1.852 exactly. When converting wind speeds, note that the Beaufort scale descriptions reference specific ranges in knots. For scientific calculations, always convert to m/s first to maintain consistency with other SI units in equations.

Practical Examples

A highway speed limit of 120 km/h equals 74.56 mph. The world 100-meter sprint record of 9.58 seconds represents an average speed of 10.44 m/s or 37.58 km/h. A typical cruising speed for a commercial aircraft is 480 knots (889 km/h or 552 mph). The speed of sound at sea level is approximately 343 m/s, 1,235 km/h, or 767 mph. A moderate breeze (Beaufort 4) blows at 13 to 18 knots (24 to 33 km/h).

Related Calculators

Pace CalculatorConvert between pace and speed for running and cycling.Fuel Cost CalculatorCalculate fuel costs for any trip based on distance and consumption.

Related Converters

Length Converter Meters, feet, inches, miles and more. Weight Converter Kilograms, pounds, ounces, stones. Temperature Converter Celsius, Fahrenheit, Kelvin. Volume Converter Liters, gallons, cups, fluid ounces. Area Converter Square meters, acres, hectares. Cooking Converter Cups to grams by ingredient. All Unit Converters Browse all conversion categories in one place.

Popular Calculators

Percentage Calculator Calculate percentages, increases, differences. Fuel Cost Calculator Estimate fuel costs for any trip. Tip Calculator Split bills and calculate tips easily. Discount Calculator Find sale prices and savings.

FAQ

How do I convert km/h to mph?
Divide the km/h value by 1.60934, or multiply by 0.621371 for the same result. For example, 100 km/h equals approximately 62.14 mph, and 130 km/h (a common European highway limit) equals about 80.78 mph. For quick mental math, multiply km/h by 0.6 and add 2-3% — this gives a close estimate without a calculator. The conversion factor comes from the fact that 1 mile = 1.60934 kilometers.
What is the difference between knots and mph?
A knot is one nautical mile per hour (1.852 km/h), while a mph is one statute mile per hour (1.609 km/h). One knot equals approximately 1.151 mph. Knots are used in maritime and aviation, while mph is used for road speed in the US and UK.
Why is m/s the SI unit of speed?
Meters per second (m/s) is the SI unit because it derives directly from the two base SI units: the meter for distance and the second for time. This makes it the natural unit in physics equations like velocity, acceleration (m/s²), and kinetic energy (½mv²). In everyday life, km/h or mph are more intuitive, but scientists and engineers use m/s for consistency across calculations. To convert: 1 m/s = 3.6 km/h = 2.237 mph.
How fast is 1 m/s in km/h?
1 m/s equals exactly 3.6 km/h or about 2.24 mph. The conversion works because there are 3,600 seconds in an hour and 1,000 meters in a kilometer (3600/1000 = 3.6). To convert m/s to km/h, multiply by 3.6. To convert back, divide by 3.6. Practical examples: walking speed is about 1.4 m/s (5 km/h), a sprinter runs at ~10 m/s (36 km/h), and a car at city speed is ~14 m/s (50 km/h).
What speed unit is used in aviation?
Aviation uses knots (nautical miles per hour) for airspeed and ground speed, and feet per minute for climb/descent rates. Knots are standard because nautical miles relate directly to degrees of latitude, making navigation calculations simpler.
How do I convert feet per second to mph?
Multiply ft/s by 0.681818 to get mph, or divide by 1.46667. For example, 100 ft/s equals approximately 68.18 mph. Feet per second is commonly used in ballistics and some engineering fields.
What are the speed limits in the US and UK?
In the US, interstate highway limits are typically 65–75 mph (105–120 km/h), urban roads 25–35 mph, and school zones 15–25 mph. In the UK, motorway limit is 70 mph (113 km/h), single carriageways 60 mph, and built-up areas 30 mph. Both countries use mph, unlike most of the world.
What is Mach number and how is it calculated?
Mach number is the ratio of an object's speed to the speed of sound in the surrounding medium. Mach 1 at sea level and 15 °C is approximately 340 m/s (1,225 km/h or 761 mph). To calculate: Mach = your speed ÷ speed of sound. Supersonic aircraft like Concorde cruised at Mach 2 (about 2,450 km/h).
How fast is the speed of sound and speed of light?
The speed of sound in dry air at 20 °C is about 343 m/s (1,235 km/h). The speed of light in a vacuum is exactly 299,792,458 m/s — roughly 1,079,252,848 km/h or about 186,282 miles per second. Light is approximately 874,000 times faster than sound.
How do I convert running pace (min/km) to speed (km/h)?
Divide 60 by your pace in minutes per kilometer. For example, a pace of 5:00 min/km equals 60 ÷ 5 = 12 km/h. A pace of 6:00 min/km equals 10 km/h. For min/mile, divide 60 by your pace to get mph. Most GPS watches display both pace and speed.
What is the Beaufort wind scale?
The Beaufort scale (0–12) describes wind speed by observable effects. Force 0 is calm (< 1 km/h), Force 6 is a strong breeze (39–49 km/h), Force 8 is a gale (62–74 km/h), and Force 12 is a hurricane (≥ 118 km/h or 64 knots). Meteorologists and sailors use this scale alongside km/h, mph, and knots.
How do speed cameras measure speed?
Speed cameras use radar (Doppler effect), laser (LIDAR), or induction loops in the road. Radar guns measure the frequency shift of reflected radio waves. LIDAR devices fire laser pulses and time their return. Average-speed cameras calculate speed by dividing the distance between two cameras by the travel time. Results are recorded in mph (UK/US) or km/h (Europe).
What are typical cycling speeds in km/h and mph?
A casual recreational cyclist averages 15–20 km/h (9–12 mph). A fit commuter rides at 20–25 km/h (12–16 mph). Road cyclists typically average 30–35 km/h (19–22 mph), while professional Tour de France riders sustain over 40 km/h (25 mph) in flat stages. Sprint speeds can exceed 70 km/h (43 mph) on a descent.
What is the formula to convert knots to km/h?
Multiply knots by 1.852 to get km/h. For example, 30 knots × 1.852 = 55.56 km/h. To convert back, divide km/h by 1.852. One knot equals exactly 1 nautical mile per hour, and a nautical mile is defined as 1,852 meters.
How does wind speed affect flight and what units are used?
Wind speed is critical in aviation. Headwinds reduce ground speed and increase flight time; tailwinds do the opposite. Crosswinds affect takeoff and landing safety. Pilots use knots as the standard unit — a Boeing 737 lands at around 130–140 knots (240–260 km/h). METAR weather reports and air traffic control communications all use knots.