What's the difference between km/h and mph?

Kilometers per hour (km/h) is the standard unit of speed in most countries using the metric system, while miles per hour (mph) is primarily used in the United States, United Kingdom, and a few other nations. The conversion factor is 1 mph = 1.60934 km/h, or conversely, 1 km/h = 0.621371 mph. For quick mental estimates: 100 km/h ≈ 62 mph, 60 mph ≈ 97 km/h. Speed limit signs differ dramatically—a US highway at 70 mph would show 113 km/h in Europe. Understanding both units is essential for international travel, importing vehicles, and comparing performance specifications.

When should I use meters per second (m/s)?

Meters per second (m/s) is the SI (International System) base unit for velocity and is universally used in physics, engineering, and scientific calculations. It's preferred because it integrates seamlessly with other SI units (meters, kilograms, seconds) in formulas for kinetic energy, momentum, acceleration, and force. Common applications: sprint speeds (Usain Bolt's record: 12.4 m/s), projectile motion, fluid dynamics, sound speed (343 m/s in air), and orbital velocities. Converting: 1 m/s = 3.6 km/h = 2.237 mph. While less intuitive for everyday speeds, m/s is essential for scientific accuracy and international standardization.

What are knots and why do ships and planes use them?

A knot equals one nautical mile per hour (1.852 km/h or 1.151 mph). Maritime and aviation industries use knots because nautical miles are based on Earth's geometry—one nautical mile equals one minute of latitude, making navigation calculations simpler. When a ship travels at 20 knots, it covers 20 nautical miles per hour, corresponding directly to movement across latitude lines on charts. This historical measurement system remains standard because charts, protocols, and international agreements are built around it. Commercial jets cruise at 450-550 knots (830-1020 km/h), cargo ships travel at 15-25 knots (28-46 km/h).

How fast is 100 km/h in different units?

100 km/h converts to: 62.14 mph (common highway speed in metric countries), 27.78 m/s (useful for physics calculations), and 53.99 knots (moderate boat speed). To visualize: 100 km/h means traveling 1 kilometer in 36 seconds, or about 28 meters every second. It's a typical highway cruising speed in Europe, Canada, and Australia. In the US, this would be equivalent to driving at approximately 60-65 mph on an interstate. For athletes, Olympic sprinters reach about 10 m/s (36 km/h) at peak speed—meaning 100 km/h is nearly 3 times faster than the fastest human runners.

What's the speed of sound in different units?

The speed of sound at sea level (15°C) is approximately 343 m/s, which converts to 1,235 km/h, 767 mph, or 666 knots. This is also known as Mach 1. Aircraft speeds are often expressed in Mach numbers (multiples of sound speed): subsonic ( Mach 5). The Concorde cruised at Mach 2.04 (2,179 km/h or 1,354 mph). Modern fighter jets reach Mach 2-3. The speed of sound varies with temperature and altitude—it's slower at higher altitudes where air is colder and thinner. Bullet speeds range from 300-1,200 m/s (1,080-4,320 km/h) depending on type.

How do I convert speed for running and cycling?

Running speeds: Walking pace is 5-6 km/h (3-4 mph), jogging is 8-10 km/h (5-6 mph), running is 12-15 km/h (7.5-9.5 mph), and marathon pace is typically 12-21 km/h (7.5-13 mph) depending on fitness. Elite marathoners maintain about 20 km/h (12.4 mph or 5:36/mile pace). Cycling speeds: Casual cycling is 15-20 km/h (9-12 mph), fitness cycling is 25-30 km/h (15-19 mph), racing cyclists sustain 40-45 km/h (25-28 mph), and Tour de France average stage speeds exceed 40 km/h. For training zones, convert your target pace to match local treadmill or cycling computer units. Most fitness trackers allow unit switching.

What are typical speed limits around the world?

Urban areas: typically 50 km/h (30 mph) globally, with school zones at 30 km/h (20 mph). Rural roads: 80-100 km/h (50-62 mph) in most countries. Highways: Europe typically 120-130 km/h (75-80 mph), US interstates 65-80 mph (105-130 km/h), Canada 100-110 km/h (62-68 mph), Australia 100-110 km/h. Notable exceptions: German Autobahn sections have no speed limit (advisory 130 km/h), while some US states have 85 mph (137 km/h) limits. Speed enforcement varies—many European countries use average speed cameras over distance, while the US primarily uses point speed detection. Understanding local speed units is crucial for legal compliance and safety when traveling.

How fast do animals move in different speed units?

Fastest animals: Cheetah reaches 120 km/h (75 mph or 33 m/s) in short bursts, making it Earth's fastest land animal. Pronghorn antelope sustains 88 km/h (55 mph) for longer distances. Peregrine falcon dives at 390 km/h (242 mph or 108 m/s)—the fastest animal movement. Horse gallop: 65-70 km/h (40-43 mph). Greyhound: 70 km/h (43 mph). Human sprinter: 37-44 km/h (23-27 mph) peak speed. Slower animals: Sloth moves at 0.24 km/h (0.15 mph), snail at 0.05 km/h. These comparisons help contextualize converted speeds—if your conversion shows 120 km/h, that's cheetah-level speed; 10 km/h is a comfortable human jog.

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Speed Converter

Convert speed between km/h, mph, m/s, and more

Speed Converter

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What is Speed Converter?

A speed converter converts velocity between different units: miles per hour (mph), kilometers per hour (km/h), meters per second (m/s), feet per second (ft/s), knots (nautical miles per hour), and Mach number (speed relative to sound). Essential for international travel understanding speed limits, aviation and maritime navigation, scientific calculations, sports performance tracking, and comparing velocities across different measurement systems. Common conversions: 60 mph ≈ 97 km/h, 100 km/h ≈ 62 mph, 1 Mach ≈ 767 mph at sea level.

Key Benefits & Use Cases

Navigate safely internationally by understanding speed limits in unfamiliar units: driving in Europe with 100 km/h limit equals 62 mph, not overly slow or dangerously fast. Convert running/cycling pace for international races: 10 mph cycling = 16 km/h. Understand aviation speeds: commercial jets cruise at 450-575 mph (Mach 0.75-0.85), while Concorde flew Mach 2 (1,354 mph). Maritime navigation uses knots: 1 knot = 1.15 mph, so 20-knot speed = 23 mph. Scientific calculations requiring m/s (physics standard SI unit): 60 mph = 26.8 m/s. Compare athletic performances across countries using different measurements. Understand wind speeds: hurricane Category 1 starts at 74 mph (119 km/h, 64 knots).

How to Use This Calculator

Enter speed value and select current unit (mph, km/h, m/s, ft/s, knots, Mach), then choose target unit for conversion or view all conversions simultaneously. Results show precise converted value. Key conversions: mph × 1.609 = km/h, km/h × 0.621 = mph, mph × 0.447 = m/s, m/s × 2.237 = mph, mph × 0.869 = knots, knots × 1.151 = mph. For Mach conversions, specify altitude as speed of sound varies: Mach 1 = 767 mph at sea level, 660 mph at 35,000 feet. Common references: walking 3 mph, jogging 6 mph, cycling 15 mph, highway driving 65 mph, airplane cruising 500 mph, Mach 1 supersonic. Use for trip planning, understanding vehicle specifications in different markets, scientific calculations.