Speed Converter

Convert between mph, km/h, m/s, knots, Mach, and more. Instant speed unit conversion with common reference speeds.

Speed Units

Miles per hour

mph

Kilometers per hour

km/h

Meters per second

m/s

Knot

Feet per second

ft/s

Mach (sea level, 20°C)

Mach

Speed of light (c)

How Fast Is That?

Walking19.84×

Cycling4.27×

Car highway (100 km/h)1.00×

Cheetah (top speed)0.96×

Commercial aircraft0.11×

Speed of sound (20°C)0.08×

How to Use Speed Converter

1Enter a speed value in any unit field.
2All other speed units update instantly.
3Compare with reference speeds like the speed of sound.

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Frequently Asked Questions

How do I convert mph to km/h?▾

1 mph = 1.60934 km/h. To convert mph to km/h: multiply by 1.60934. To convert km/h to mph: divide by 1.60934 (or multiply by 0.621371). Quick mental math: km/h to mph — multiply by 0.6. mph to km/h — multiply by 1.6. Common conversions: 30 mph = 48.3 km/h. 60 mph = 96.6 km/h. 100 km/h = 62.1 mph. 120 km/h = 74.6 mph. Speed limits: US/UK mostly use mph (25, 35, 55, 65, 70 mph). Europe/Canada/Australia use km/h (50, 80, 110, 130 km/h). Highway speed 100 km/h = 62 mph.

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

A knot = 1 nautical mile per hour = 1.15078 mph = 1.852 km/h. Used in aviation and maritime navigation because: 1 nautical mile ≈ 1 minute of arc of latitude — so knots directly relate to geographic coordinates. A plane flying at 500 knots covers about 500 minutes of arc (= 8.33 degrees) of latitude per hour. This makes navigation calculations simpler. Weather: wind speeds are often reported in knots internationally. Aircraft speed: commercial airliners cruise at 450–500 knots (840–925 km/h). Ships: cargo ships cruise at 14–25 knots, warships at 30+ knots.

What is Mach number?▾

Mach number = Speed of object ÷ Speed of sound in the medium. Mach 1 = speed of sound ≈ 343 m/s = 1,235 km/h = 767 mph at sea level (20°C). Important: speed of sound varies with temperature and medium. At -50°C (high altitude cruising): ≈ 299 m/s = 1,079 km/h. In water: ≈ 1,480 m/s. Mach regimes: Subsonic < 0.8. Transonic: 0.8–1.2. Supersonic: 1.2–5. Hypersonic: 5+. Commercial aircraft cruise at Mach 0.82–0.86. Concorde: Mach 2.04. SR-71 Blackbird: Mach 3.3+. Space Shuttle re-entry: Mach 25.

What is the speed of light and how fast is it?▾

Speed of light (c) in vacuum = 299,792,458 m/s = 299,792 km/s ≈ 186,282 miles per second. Light travels: 1 foot in 1 nanosecond (approximately). From Moon to Earth in ~1.3 seconds. From Sun to Earth in ~8.3 minutes. From Earth to Mars (average distance): 3–22 minutes. From Earth to nearest star (Proxima Centauri): 4.24 years. The speed of light is the universal speed limit — according to special relativity, nothing with mass can reach it. GPS satellites must account for relativistic effects because the speed difference between satellite and ground creates measurable time dilation.

How fast do things move in everyday life?▾

Reference speeds: Walking: 1.4 m/s = 5 km/h = 3.1 mph. Cycling: 5–8 m/s = 18–29 km/h = 11–18 mph. Usain Bolt (peak): 12.4 m/s = 44.7 km/h = 27.8 mph. Cheetah (top speed): 29 m/s = 104 km/h = 65 mph. Commercial aircraft: 250 m/s = 900 km/h = 560 mph. Sound in air (20°C): 343 m/s = 1,235 km/h = 767 mph. Bullet (rifle): 900 m/s = 3,240 km/h = 2,014 mph. Space Shuttle: 7,800 m/s = 28,000 km/h = 17,400 mph. Earth orbiting Sun: 30,000 m/s = 108,000 km/h.

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