Speed Calculator

How to use this calculator

Select what you want to find from the “Solve for” dropdown: Speed, Distance, or Time. Enter the two known values. Use the distance and speed unit selectors to work in your preferred units. The calculator handles all conversions automatically.

Tap a preset (100m Sprint, Marathon, City Driving, Highway, Speed of Sound) to auto-fill typical values. Press Calculate to see the result in multiple units plus running pace.

Speed vs velocity: the essential distinction

Speed and velocity are often used interchangeably in everyday speech, but in physics they are distinct:

Speed is a scalar: it has magnitude but no direction. It is always positive (or zero). “60 km/h” is a speed.

Velocity is a vector: it has both magnitude and direction. It can be negative in 1D if you define a positive direction. “60 km/h heading north” is a velocity.

The magnitude of velocity equals speed. The key difference appears when direction changes. A car completing a loop is back at the start: average velocity is zero (no net displacement) but average speed is the total distance divided by time.

The speed formula

The relationship between speed, distance, and time:

These three versions of the same equation solve for any one variable given the other two. The SI unit of speed is metres per second (m/s). Other common units: km/h, mph, ft/s, knots (nautical miles per hour).

Speed unit conversions

From	To	Multiply by
m/s	km/h	3.6
m/s	mph	2.237
km/h	m/s	0.2778
km/h	mph	0.6214
mph	m/s	0.4470
mph	km/h	1.6093
knots	km/h	1.852
knots	mph	1.151

A car at the UK motorway limit (70 mph) travels at 70 × 0.447 = 31.3 m/s = 112.7 km/h.

Speed records

Human sprint: Usain Bolt’s 100m world record (9.58 s, 2009) gives an average of 10.44 m/s (37.6 km/h). His peak speed during the race was approximately 12.4 m/s (44.7 km/h) at around 65 metres.

Human swimming: The world record in the 50m freestyle gives average speeds around 2.4 m/s (8.6 km/h). Top swimmers sprint at about 2.5 m/s.

Land vehicles: The land speed record is held by ThrustSSC (1997) at 763 mph (1,228 km/h = 341 m/s), breaking the sound barrier on land.

Aircraft: The SR-71 Blackbird holds the air-breathing jet speed record at Mach 3.3 (approximately 3,540 km/h = 984 m/s).

Spacecraft: The Parker Solar Probe will reach approximately 692,000 km/h (192 km/s) at perihelion, the fastest human-made object.

Light: 299,792,458 m/s in vacuum. Nothing with mass can reach this speed.

Average speed in multi-stage journeys

For a journey with multiple stages at different speeds, the overall average speed is NOT the arithmetic mean of the stage speeds. It is total distance divided by total time.

For equal distances at different speeds, the correct average is the harmonic mean: 2/(1/v₁ + 1/v₂).

Running pace

Pace is the inverse of speed, expressing time per unit distance rather than distance per unit time. Runners typically use pace in minutes per kilometre or minutes per mile.

Common running benchmarks:

• Recreational runner: 6-8 min/km (2.1-2.8 m/s)
• Competitive amateur: 4-5 min/km (3.3-4.2 m/s)
• Elite marathon: 2:50-3:10 min/km (5.3-5.9 m/s)
• World marathon record (Kipchoge): 2:51 min/km (5.85 m/s)

Speed of sound and Mach number

The speed of sound in dry air at 20°C is approximately 343 m/s (1234 km/h, 767 mph). It depends on temperature:

where T is temperature in kelvin. At altitude where aircraft fly (-56°C), the speed of sound drops to about 295 m/s.

Mach number is the ratio of an object’s speed to the local speed of sound:

Mach 1 = speed of sound (transonic). Mach > 1 = supersonic. Mach > 5 = hypersonic. The shock wave (sonic boom) produced when an aircraft exceeds Mach 1 carries enormous energy and is heard as a loud bang from the ground.

Speed of sound in other media: water ≈ 1,480 m/s, steel ≈ 5,120 m/s, diamond ≈ 12,000 m/s. Sound travels faster in denser, stiffer materials.

Speed measurement technology

Radar guns: Emit radio waves and measure the Doppler frequency shift of the reflected signal. The frequency change is proportional to the object’s speed relative to the gun. Used by traffic police and in baseball pitch measurement.

GPS: Calculates speed from consecutive position fixes. Time between fixes is known (typically 1 second), and the distance change gives speed. Modern GPS also uses Doppler shift of satellite signals for more precise instantaneous speed.

Pitot tube: Measures airspeed in aircraft by comparing static pressure and dynamic pressure (stagnation pressure). The difference gives airspeed through Bernoulli’s equation. Pitot tubes must be heated to prevent icing.

Optical sensors: Laser barriers and photo-gate timing in sprinting competitions. Two sensors separated by a known distance measure the time for a runner to pass between them.