Speed Converter

How to Use This Converter

Enter a value and pick your units. Pick your mode at the top: Single Conversion for two-unit conversions, Convert to All for a full breakdown, Pace Calculator for runners and cyclists, or Speed Reference for common speeds by category.

Type your value, select units, click Convert. Use the swap button to reverse direction.

Preset buttons load common starting values—walking pace, highway speeds, speed of sound. Quick conversion buttons load popular unit pairs, handy for repeat conversions. Adjust decimal places and other display options in the Options panel.

Miles per Hour vs Kilometers per Hour

Miles per hour and kilometers per hour are the two speed units most people encounter daily. The US, UK (for roads), and a handful of other countries use mph. Everyone else uses km/h. Most of the world. Travelers, car buyers comparing foreign specs, and anyone handling international data deal with this regularly.

The exact factor: 1 mph = 1.60934 km/h. For mental math, multiply mph by 1.6 to get km/h, or multiply km/h by 0.6 to get mph. Close enough for estimation. Another trick: multiply mph by 8, divide by 5.

Knots Explained

One knot = one nautical mile per hour. It has measured ship and aircraft speeds for centuries. The nautical mile corresponds to one minute of arc of latitude, making navigation calculations simpler. One knot = 1.852 km/h exactly, or about 1.151 mph.

Sailors coined it while measuring speed with a chip log—a wooden panel on a knotted rope tossed overboard. They'd count knots passing through their hands over a set time. The name stuck. Aviation uses knots for the same reasons, and it's now the global standard for airspeed, wind speed, and ground speed. Adding roughly 15% converts knots to mph; multiplying by 1.85 gives km/h.

Meters per Second — The Scientific Standard

The SI unit for speed is meters per second (m/s), used across physics, engineering, and scientific research. Based on meters and seconds, the core SI units.

Key conversions: multiply m/s by 3.6 for km/h, by 2.237 for mph, or by 3.281 for ft/s. Used in scientific papers, weather reports, and physics.

Benchmarks in m/s: walking is 1.4, jogging hits 2.8, highway driving (100 km/h) equals 27.8, and the speed of sound at sea level runs 343. Earth's escape velocity? About 11,186 m/s. The unit scales well to extremes.

Mach Number and the Speed of Sound

Mach number compares an object's speed to the local speed of sound, named for physicist Ernst Mach. The catch: Mach 1 isn't a fixed speed. It changes with temperature and medium—and most people don't realize it. This converter uses the standard sea-level value at 20°C: 343 m/s or 767 mph.

Sound travels through molecular collisions, so temperature changes the speed. Warmer air means faster molecules, faster sound. At cruising altitude (11 km up, around -56°C), the speed of sound drops to roughly 295 m/s. Altitude changes everything. An aircraft at Mach 0.85 at altitude is moving slower in absolute terms than Mach 0.85 at sea level.

A sonic boom is the shock wave cone that trails any supersonic object.

Light Speed

Nothing outruns light in a vacuum—it's the universe's speed ceiling. Since 1983, it's been defined as exactly 299,792,458 m/s. The meter is now defined based on light speed, not the other way around. Relativity depends on this constant.

In familiar units, light's speed produces huge numbers: 670,616,629 mph, or 186,282 miles per second. Light circles Earth 7.5 times per second. It reaches the Moon in 1.28 seconds, the Sun in 8.3 minutes, and Proxima Centauri in 4.24 years.

How slow are we by comparison? Highway driving at 100 km/h is 9.27 × 10⁻⁸ c—less than one ten-millionth of light speed. The Parker Solar Probe, the fastest human-made object, hits just 0.064% of c. Even Earth's orbital speed (30 km/s) is only 0.01% of light speed. Barely moving.

Practical uses: GPS satellites account for relativistic time dilation. Fiber optic communications push data at about two-thirds light speed through glass. Deep space communication involves minutes or hours of lag.

Beaufort Wind Scale

Developed by Admiral Beaufort in 1805, this scale gave sailors a consistent method to estimate wind from sea conditions. It runs from Force 0 (calm) to Force 12 (hurricane), each level defined by visible effects, not measured speeds.

• Force 0–3 (up to 12 mph): Smoke drifts, leaves rustle
• Force 4–5 (13–24 mph): Dust rises, small branches move
• Force 6–7 (25–38 mph): Walking difficult, whole trees sway
• Force 8–9 (39–54 mph): Twigs break, minor structural damage
• Force 10–11 (55–72 mph): Trees uprooted, widespread damage
• Force 12 (73+ mph): Severe destruction

Weather forecasts still use the scale, mostly in marine forecasts. Many people find "gale-force winds" more intuitive than "35 knots."

Speed in Weather

Wind speed units vary by audience: mph in US public forecasts, km/h elsewhere, knots for marine and aviation, m/s in scientific reports. Useful when reading forecasts from different sources.

Hurricane intensity uses the Saffir-Simpson scale:

• Category 1: 74–95 mph
• Category 2: 96–110 mph
• Category 3: 111–129 mph
• Category 4: 130–156 mph
• Category 5: 157+ mph

Tornadoes work differently. The Enhanced Fujita scale rates them from EF0 (65–85 mph) to EF5 (200+ mph), but ratings come from damage surveys after the fact. The strongest tornado winds on record topped 300 mph—unmatched by any other atmospheric phenomenon.

Speed in Sports

Ball and puck speeds in professional sports reach surprising levels. Baseball fastballs routinely hit 95 mph (153 km/h), with records over 105 mph. Pro tennis serves average 115–130 mph; the record stands at 163.7 mph. Golf drives launch at 150–180 mph. Hockey slap shots reach 90–105 mph.

The fastest object in any racquet sport? A badminton shuttlecock at 306 mph right off the racquet—though drag slows it fast. Jai alai balls hit 188 mph. Racing speeds vary widely: elite marathon pace sits around 13 mph over 26.2 miles, pro cyclists sustain 25–28 mph, NASCAR hits 180–200 mph, Formula 1 tops 220 mph, and Top Fuel dragsters break 330 mph from a standstill in under 4 seconds.

Speed Limits Around the World

Highway limits come down to national priorities. US interstates typically allow 65–75 mph, with some Texas toll roads at 85 mph. Canada uses 100–120 km/h (62–75 mph). Mexico sets 110 km/h (68 mph).

Europe tends to set higher limits: 120–130 km/h (75–81 mph). Germany's Autobahn has advisory limits of 130 km/h but no maximum on many stretches. Traffic and conditions slow most drivers down regardless. Almost nobody sustains 150 mph.

Driving abroad? Signs without units use the local standard—mph in the US and UK, km/h everywhere else. "100" in Canada means 100 km/h (62 mph). Enforcement and camera tolerances vary wildly.

Mental Math Shortcuts

A handful of memorized conversions cover most mental math:

• mph → km/h: multiply by 1.6
• km/h → mph: multiply by 0.6
• m/s → km/h: multiply by 3.6
• m/s → mph: multiply by 2.24
• knots → mph: add about 15%
• mph → knots: subtract about 13%

Use these as reference points: 100 km/h = 62 mph = 28 m/s = 54 knots. Double or halve from there. Speed of sound (343 m/s = 767 mph = 1,235 km/h) anchors high-speed estimates.