PhysicsCalcs
Units & Conversions

Speed Converter

Convert km/h to mph, mph to km/h, m/s to km/h, knots to mph, Mach to km/h, speed of sound, and speed of light with verified factors.

Interactive converter

Speed Converter

Convert meters per second, km/h, mph, feet per second, knots, Mach, speed of sound, speed of light, and more.

Speed magnitude is normally non-negative. Mach and sound-speed units use stated assumptions.

From
To

Result

Enter a value and click Convert to see the conversion.

Quick Guide

  • Enter speed magnitude (non-negative).
  • Mach and sound-speed units show assumption warnings.
  • Reference speeds are approximate except c.

Table of Contents

Key Takeaways

  • Speed is distance divided by time; SI unit is m/s.
  • 1 m/s = 3.6 km/h; 1 mph = exactly 1.609344 km/h.
  • 1 knot = 1 nautical mile/h = 1.852 km/h.
  • Mach depends on local speed of sound; Mach 1 ≈ 343 m/s at 20°C dry air.
  • Speed of light in vacuum c = 299,792,458 m/s exactly.

What Is a Speed Converter?

It converts speed magnitudes between metric, imperial, nautical, and physics reference units using m/s internally.

Combine with the Length Converter and Time Converter for v = d/t problems, or the Fuel Consumption Converter for vehicle efficiency.

How to Use the Speed Converter

  1. 1Enter a non-negative speed value.
  2. 2Select from and to units, or use All units mode.
  3. 3Click Convert — results scroll into view.
  4. 4Read warnings for Mach and reference sound speeds.
  5. 5Try presets for km/h ↔ mph or Mach conversions.

Speed Formula

v=d/tv = d / t

v = speed, d = distance, t = time.

Speed vs Velocity

This converter handles speed magnitude only, not direction. Signed velocity belongs in motion calculators.

Common Speed Units

Unitm/sUse
m/s1SI, physics
km/h0.2778Road speed
mph0.44704US/UK roads
knot0.514444Aviation, marine

km/h, mph, and m/s

1 m/s = 3.6 km/h. 1 mph = 0.44704 m/s exactly. 1 km/h = 0.277778 m/s.

km/h to mph Quick Reference

km/hmphm/s
6037.2816.67
8049.7122.22
10062.1427.78
12074.5633.33

Knots and Nautical Speed

1 knot = 1 international nautical mile per hour = 1.852 km/h. Used in ships, aircraft, and weather.

Mach Number and Speed of Sound

Mach=v/aMach = v / a

Mach is a dimensionless ratio (speed ÷ local speed of sound). This converter treats Mach as a speed unit using Mach 1 ≈ 343 m/s in dry air at 20°C. Actual Mach 1 varies with temperature and medium.

Speed of Light

c = 299,792,458 m/s in vacuum (exact). Sound in water and Earth orbital speed are approximate reference values.

Examples

100 km/h

100 km/h ≈ 62.137 mph ≈ 27.778 m/s.

1 knot

1 kn = 1.852 km/h.

Mach 1

Mach 1 ≈ 343 m/s ≈ 1,234.8 km/h at 20°C air.

Common Mistakes

Assuming Mach is a fixed speed everywhere. Using sound speed without stating medium/temperature. Confusing knots with mph.

Limitations

Sound speed varies with temperature, humidity, and pressure. Not for aviation or marine navigation certification.

FAQ

How do you convert km/h to mph?›

Multiply km/h by 0.621371, or divide by 1.609344. Example: 100 km/h ≈ 62.137 mph.

How many km/h are in 1 m/s?›

1 m/s = 3.6 km/h exactly.

What is a knot?›

One international nautical mile per hour = 1.852 km/h = 0.514444 m/s.

Is knot the same as mph?›

No. 1 knot = 1.852 km/h; 1 mph = 1.609344 km/h.

What is Mach number?›

Object speed divided by local speed of sound. Mach 1 changes with temperature and medium.

What is the speed of light?›

299,792,458 m/s in vacuum (exact by definition).

How do I convert mph to km/h?›

Multiply mph by 1.609344. Example: 60 mph = 96.56064 km/h.

What is the difference between speed and velocity?›

Speed is scalar magnitude. Velocity includes direction.

Sources

  1. BIPM: SI Brochure
  2. NIST SP 811
Manish Kumar

Author & technical reviewer

Manish Kumar

PhysicsCalcs tools are reviewed with an educational focus: clear formulas, transparent assumptions, and practical context for students and science learners.

Learn more about Manish