Speed Converter
Convert any speed unit instantly — km/h, mph, m/s, knots, Mach, and the speed of light. Built-in running pace calculator, Beaufort wind scale reference, and real-world speeds from a snail to light. Free, instant, and privacy-first.
Mach values use speed of sound at sea level (20°C) = 340.29 m/s. Actual Mach varies with altitude and temperature.
All Speed Units
At this speed you travel 27.8 m every second. Typical highway speed.
= 9.2657e-6% of the speed of light. Light would travel this speed 10,790,000× faster.
Popular Conversions
Driving — international travel
Driving — US visitors abroad
Aviation and maritime
Aviation and maritime
Science and weather
Aviation
Science to everyday
Engineering
Running & Cycling Pace Converter
The feature athletes bookmark — convert speed ↔ pace with race finish time estimator.
Speed → Pace
Pace → Speed
Race Finish Time
Uses pace from Section B above.
Estimated finish:
42.195km at 6:00 min/km
Wind Speed & Beaufort Scale
| Beaufort | Description | km/h |
|---|---|---|
| 0 | Calm | < 1 |
| 1 | Light air | 1–5 |
| 2 | Light breeze | 6–11 |
| 3 | Gentle breeze | 12–19 |
| 4 | Moderate breeze | 20–28 |
| 5 | Fresh breeze | 29–38 |
| 6 | Strong breeze | 39–49 |
| 7 | High wind | 50–61 |
| 8 | Gale | 62–74 |
| 9 | Strong gale | 75–88 |
| 10 | Storm | 89–102 |
| 11 | Violent storm | 103–117 |
| 12 | Hurricane | ≥ 118 |
Click any Beaufort row to load its minimum speed into the main converter.
How to Convert Speed Units
- Enter your speed value in the input field and select your unit from the dropdown
- All speed units update instantly in the output grid below
- Click any unit to make it the new reference for bidirectional conversion
- Use the Popular Conversions panel for the most searched pairs
- Use the Running Pace Converter for athletics pace calculations
- Use the Beaufort Scale panel for wind speed reference
Understanding Speed Units
km/h is the everyday standard in most countries for road speeds. m/s is the SI unit used in physics and meteorology. Converting between them is simple: multiply m/s by 3.6 to get km/h.
Miles per hour is the everyday standard in the US and UK for road speeds. 1 mph = 1.60934 km/h.
Used in maritime and aviation. One knot = one nautical mile per hour = 1.852 km/h. Nautical miles relate to Earth's geographic coordinates, making knots valuable for navigation.
The ratio of speed to the local speed of sound. Mach 1 = speed of sound at sea level (≈1,235 km/h). The value varies with altitude and temperature.
The universal speed limit: exactly 299,792,458 m/s. Used in astrophysics and relativity. Nothing with mass can reach this speed.
Running Pace vs Speed
Running pace (min/km or min/mile) is the inverse of speed — instead of distance per unit time it is time per unit distance. A runner doing 6:00 min/km is running at 10 km/h. Pace is preferred by runners because it directly tells you how long each kilometer or mile will take, making it easier to plan race strategy and monitor effort. This converter handles pace ↔ speed conversion and race finish time estimation for all standard race distances.
The Beaufort Wind Scale
The Beaufort scale was developed by Royal Navy Admiral Sir Francis Beaufort in 1805 as a way to standardize wind speed descriptions for ship captains without instruments. It runs from 0 (calm) to 12 (hurricane). Each level corresponds to observable effects on land and sea — making it practically useful without requiring instruments. It was officially adopted by the British Admiralty in 1838 and remains in use in meteorology worldwide.
Key Features
- 13 speed units across metric, imperial, nautical, and scientific systems
- All units shown simultaneously — click any to make it the reference
- Unit category filter (All / Metric / Imperial / Nautical / Scientific)
- Popular conversions quick panel for 8 most searched pairs
- Running and cycling pace converter with race finish time estimator
- Beaufort wind scale with interactive reference table (13 levels)
- Real-world speed reference from snail to speed of light
- Context panels for driving, aviation, and physics
- Conversion history (last 10)
- Works on all devices including mobile
- 100% free — no signup, no account, no data uploaded
100% Free & 100% Private
All processing happens entirely in your browser. We never upload your data to any server. No signup, no account, no hidden fees. Just free, secure tools.
Frequently Asked Questions
How do I convert km/h to mph?
Multiply km/h by 0.621371 to get mph. Example: 100 km/h × 0.621371 = 62.14 mph. To convert mph to km/h multiply by 1.60934. Example: 60 mph × 1.60934 = 96.56 km/h.
How many mph is a knot?
One knot equals 1.15078 mph or 1.852 km/h. A knot is one nautical mile per hour. Example: 100 knots = 115.08 mph = 185.2 km/h.
How fast is Mach 1 in km/h and mph?
Mach 1 at sea level (20°C) is approximately 1,235 km/h or 767 mph. The speed of sound varies with altitude and temperature — at cruising altitude (~35,000 ft) it drops to about 1,062 km/h.
How do I convert running pace to speed?
Divide 60 by your pace in minutes per km to get km/h. Example: a 6:00 min/km pace = 60 ÷ 6 = 10 km/h. For min/mile: divide 60 by pace to get mph. Use the Pace Converter panel for instant conversion.
What is a knot and why is it used in aviation?
A knot is one nautical mile per hour. Nautical miles are based on Earth's circumference — one nautical mile equals one arcminute of latitude. Aviation and maritime navigation use knots because they directly relate to geographic coordinates, making navigation calculations simpler.
How fast is the speed of light in km/h?
The speed of light in a vacuum is exactly 299,792,458 meters per second, which equals approximately 1,079,252,848 km/h or about 670,616,629 mph. Nothing with mass can reach or exceed this speed.
What is the Beaufort scale?
The Beaufort scale is a 13-level scale (0–12) describing wind speed and its observable effects. Beaufort 0 is calm air. Beaufort 6 is a strong breeze moving large branches. Beaufort 12 is hurricane force causing devastating damage. It was developed by Admiral Francis Beaufort in 1805.
Is this speed converter free?
Yes, completely free with no account required. All conversions happen in your browser instantly. No data is sent to any server.
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