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Speed Converter

km/h, mph, m/s, knots, ft/s — and Mach.

Speed units vary by domain: roads use mph or km/h, aviation uses knots, physics uses m/s, and aerospace uses Mach numbers. This converter shows all of them at once so you can understand any speed reference regardless of its origin.

100 km/h equals
62.1371 mph
UnitValue
Meters per second27.7778 m/s
Miles per hour62.1371 mph
Knots (nautical mph)53.9957 knots
Feet per second91.1344 ft/s
Mach (speed of sound)0.081 mach

Speed Units at a Glance

Every speed unit in common use, with their relationships:

  • m/s: the SI base unit for speed, used in physics and science
  • km/h: road speeds in most of the world; wind speed in meteorology
  • mph: road speeds in US, UK, and a handful of other countries
  • knots: aviation airspeed, nautical navigation, and wind speed in aviation weather
  • ft/s: occasional US engineering use; bullet/projectile speeds
  • Mach: ratio of speed to local speed of sound (~343 m/s at sea level, 20°C)

Speed Reference Points

Anchoring unit conversions to real-world speeds makes them intuitive:

  • Walking: ~5 km/h = 3.1 mph = 1.4 m/s
  • Cycling: ~25 km/h = 15.5 mph = 6.9 m/s
  • Highway car: ~120 km/h = 74.6 mph = 33.3 m/s
  • High-speed train: ~300 km/h = 186 mph = 83.3 m/s
  • Commercial aircraft cruise: ~900 km/h = 559 mph = 486 knots = Mach 0.85
  • Speed of sound (Mach 1, sea level, 20°C): 1,235 km/h = 767 mph = 667 knots
  • Low Earth orbit: ~28,000 km/h = 17,398 mph = Mach 23

Mach Number: What It Really Means

Mach number isn't a fixed speed — it's the ratio of your speed to the local speed of sound, which changes with air temperature and therefore altitude. Mach 1 at sea level is 1,235 km/h; at cruising altitude (11,000 m, −56°C) it's only about 1,062 km/h.

  • Subsonic: below Mach 0.8
  • Transonic: Mach 0.8–1.2 (shock wave formation begins)
  • Supersonic: Mach 1.2–5.0
  • Hypersonic: above Mach 5 — friction heating becomes severe
  • Concorde cruise: Mach 2.02 (~2,180 km/h at altitude)
  • SR-71 Blackbird: Mach 3.35 — highest sustained speed for a crewed aircraft

How to Convert Speed Units

Instant multi-unit speed conversion in two steps.

  1. 1
    Enter the speed value
    Type the number. Select km/h, mph, m/s, knots, ft/s, or Mach from the dropdown.
  2. 2
    Read all units at once
    The table shows every unit simultaneously. No need to convert twice — pick whichever result you need.

FAQ

How do I convert km/h to mph?
Multiply by 0.621371. Example: 100 km/h ≈ 62.14 mph.
How fast is Mach 1?
About 343 m/s or 1,235 km/h (767 mph) at sea level, 20°C. It drops at altitude because air temperature does.
Why do ships use knots?
One knot = one nautical mile per hour, and one nautical mile = one minute of latitude. It makes navigation math with charts much cleaner.
What speed is Mach 2?
Mach 2 = 686 m/s ≈ 2,470 km/h ≈ 1,535 mph at sea level. The Concorde cruised at Mach 2.02. Most modern fighter jets can exceed Mach 2.

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