How Do You Convert mph, km/h, m/s, and Knots?
Speed is measured differently depending on where you are and what you are doing. A car speedometer in Germany shows km/h, while one in the US shows mph. A ship's navigator tracks speed in knots. A physics textbook uses meters per second. This guide explains all four units, how they relate to each other, and when each is used.
Kilometers per Hour (km/h)
Kilometers per hour (km/h) is the most widely used speed unit for road transportation. It appears on speedometers and road signs in most countries that use the metric system — which is the majority of the world.
At 100 km/h, you cover 100 kilometers (62.1 miles) in one hour. Most highway speed limits range from 100 to 130 km/h in metric countries. Urban speed limits are typically 50 km/h, and residential zones are often 30 km/h.
Miles per Hour (mph)
Miles per hour (mph) is the standard speed unit for road transportation in the United States and the United Kingdom. American and British cars show mph on their speedometers.
60 mph is a common US highway speed limit on undivided highways. Interstate highways typically have limits of 65–75 mph. Urban limits are usually 25–35 mph.
1 mph = 1.60934 km/h. To convert mph to km/h, multiply by 1.60934. To convert km/h to mph, multiply by 0.621371.
Meters per Second (m/s)
Meters per second (m/s) is the SI unit of speed, used in physics, engineering, and scientific contexts. It tells you how many meters an object travels in one second.
1 m/s = 3.6 km/h. To convert m/s to km/h, multiply by 3.6. To convert km/h to m/s, divide by 3.6.
Reference points: walking speed is about 1.4 m/s, a sprint is around 10–12 m/s, and the speed of sound is 343 m/s (at 20°C at sea level).
Knots (kn)
A knot is one nautical mile per hour, where a nautical mile equals 1,852 meters. Knots are the international standard for aviation and maritime speeds.
1 knot = 1.852 km/h = 1.15078 mph. To convert knots to km/h, multiply by 1.852.
Why nautical miles and knots? A nautical mile was originally defined as one arcminute of latitude on the Earth's surface, making navigation and chart reading much simpler. The system has persisted because it integrates directly with latitude/longitude coordinates.
Commercial aircraft cruise at 450–550 knots (830–1,020 km/h). A typical sailing yacht sails at 5–12 knots. Wind speeds in weather forecasts for aviation and marine use are given in knots.
Speed Conversion Reference
Common speed conversions across all four units:
- Walking: 5 km/h = 3.1 mph = 1.39 m/s = 2.7 kn
- City driving: 50 km/h = 31 mph = 13.9 m/s = 27 kn
- Highway: 100 km/h = 62.1 mph = 27.8 m/s = 54 kn
- High-speed train: 300 km/h = 186 mph = 83.3 m/s = 162 kn
- Speed of sound: 1,235 km/h = 767 mph = 343 m/s = 667 kn (Mach 1)
Quick Conversion Cheat Sheet
km/h to mph: multiply by 0.6214 (or divide by 1.609)
mph to km/h: multiply by 1.609
km/h to m/s: divide by 3.6
m/s to km/h: multiply by 3.6
knots to km/h: multiply by 1.852
km/h to knots: divide by 1.852
Speed in Sports: Records and Reference Points
Human running speed puts everyday units into perspective. Usain Bolt's 100 m world record of 9.58 seconds corresponds to a top speed of about 44.72 km/h (27.8 mph or 12.4 m/s). Average marathon pace for elite runners is around 20 km/h (12.4 mph) — sustained for just over two hours.
Ball sports involve much higher speeds. A professional tennis serve reaches 220–240 km/h (137–149 mph). A football shot can reach 120 km/h (75 mph). Baseball pitchers regularly throw at 145–155 km/h (90–96 mph), and cricket bowlers exceed 160 km/h (99 mph).
In motorsport, Formula 1 cars reach top speeds of around 360 km/h (224 mph) at circuits like Monza. The land speed record stands at 1,228 km/h (763 mph), set in 1997 by the ThrustSSC jet-powered car — just beyond the speed of sound. Knowing how to convert between mph and km/h lets you compare records across eras and reporting conventions.
Speed Limits Around the World
Highway speed limits vary significantly by country and road design. Germany's Autobahn has an advisory speed of 130 km/h (81 mph) on most sections but no general limit on roughly 30% of the network. France, Spain, and Italy use 130 km/h on motorways. The UK sets its motorway limit at 70 mph (113 km/h).
In the US, interstate highway limits range from 65 mph (105 km/h) in some states to 85 mph (137 km/h) on a single stretch of Texas highway — the highest posted limit in the country. Urban limits are typically 25–35 mph (40–56 km/h), with school zones at 15–20 mph (24–32 km/h).
Aviation imposes speed limits near airports. Aircraft in US-controlled airspace must fly below 250 knots (463 km/h) below 10,000 feet. This limit exists to reduce closing speeds between aircraft and give air traffic controllers more time to manage traffic safely around busy terminals.
Conclusion
The four main speed units are km/h (road transport worldwide), mph (US and UK roads), m/s (science and physics), and knots (aviation and maritime). The most common conversion is km/h to mph: multiply by 0.6214. Use our free speed converter for instant results.