About This Tool
Speed units vary by country, industry, and scientific context. Road signs in the United States use miles per hour, most of the world uses kilometers per hour, maritime and aviation industries rely on knots, physicists default to meters per second, and aerospace engineering references Mach numbers. Switching between these units requires knowing the exact conversion factors, and small rounding errors can matter when you are calculating fuel burn rates, travel times, or engineering tolerances. This Speed Converter handles six common speed units: miles per hour (mph), kilometers per hour (km/h), meters per second (m/s), feet per second (ft/s), knots, and Mach (at sea level standard conditions). Enter any value, select your source unit, and the tool instantly displays the equivalent in every other unit simultaneously. A reference table of common speeds (walking, running, highway limits, speed of sound) provides real-world context so you can quickly sanity-check your conversions. No formulas to memorize, no signup, and results update in real time as you type.
How Speed Unit Conversion Works
All speed conversions go through a common base unit: meters per second (m/s). Each unit has a known conversion factor to m/s:
- 1 mph = 0.44704 m/s
- 1 km/h = 0.27778 m/s
- 1 ft/s = 0.3048 m/s
- 1 knot = 0.51444 m/s
- 1 Mach = 343 m/s (at sea level, 20 C)
To convert from unit A to unit B: multiply by A's factor to get m/s, then divide by B's factor. For example, 60 mph to km/h: 60 x 0.44704 = 26.8224 m/s, then 26.8224 / 0.27778 = 96.56 km/h. This two-step approach ensures accuracy across all possible unit pairs.
Miles Per Hour vs. Kilometers Per Hour
The mph-to-km/h conversion is the most commonly needed speed translation. The exact ratio is:
- 1 mile = 1.609344 kilometers
- 1 mph = 1.609344 km/h
Quick mental approximation: multiply mph by 1.6 to get km/h, or multiply km/h by 0.6 to get mph. This is accurate enough for everyday use (within about 1%). For example, a 100 km/h speed limit is roughly 62 mph, and a 70 mph highway speed is about 113 km/h.
The United States, the United Kingdom (partially), and Myanmar are the main countries still using mph for road speed limits. The rest of the world uses km/h, making this conversion essential for international travel and vehicle imports.
Understanding Knots in Aviation and Sailing
A knot equals one nautical mile per hour, and one nautical mile equals 1.852 km (or 1.151 statute miles). This unit exists because it ties directly to latitude: one nautical mile is approximately one minute of arc along a great circle of the Earth.
This makes navigation calculations simpler when working with charts measured in degrees and minutes. Pilots, ship captains, and weather forecasters all report wind and travel speeds in knots. Air traffic control worldwide uses knots as the standard speed unit, and airspeed indicators in most aircraft display knots rather than mph or km/h.
To convert knots to km/h, multiply by 1.852. To convert knots to mph, multiply by 1.151. A typical commercial jet cruises at about 450-550 knots (520-630 mph, 830-1020 km/h).
Mach Numbers and the Speed of Sound
Mach number expresses speed as a ratio to the speed of sound. Mach 1 equals the speed of sound, Mach 2 is twice the speed of sound, and so on. The actual speed represented by Mach 1 varies with temperature and altitude:
- Sea level at 20 C: 343 m/s (767 mph, 1,235 km/h)
- Cruising altitude (35,000 ft): approximately 295 m/s (660 mph)
This converter uses the sea-level standard value (343 m/s) for Mach conversions. Military aircraft regularly exceed Mach 1 (supersonic), and some experimental vehicles have reached Mach 5+ (hypersonic). The Concorde cruised at about Mach 2.04, and the SR-71 Blackbird reached Mach 3.3.
Meters Per Second in Science and Engineering
Meters per second is the SI (International System of Units) standard for speed. It is used in physics equations, engineering specifications, and scientific research worldwide. Key reference points:
- Walking pace: approximately 1.4 m/s
- Olympic 100m sprint: approximately 10.4 m/s (Usain Bolt's record pace)
- Highway driving (65 mph): approximately 29 m/s
- Speed of sound: 343 m/s
- Speed of light: 299,792,458 m/s (exact, by definition)
When working with physics formulas (kinetic energy, momentum, acceleration), always convert to m/s first to ensure consistent units. The formula KE = 0.5mv^2 requires mass in kg and velocity in m/s to produce energy in joules.
Frequently Asked Questions
How accurate is the Mach conversion?
This converter uses the standard sea-level value of 343 m/s (approximately 767 mph) for Mach 1. The actual speed of sound varies with temperature and altitude. At typical cruising altitude (35,000 feet), Mach 1 is about 295 m/s (660 mph). For precise aerospace calculations, you should account for the local atmospheric conditions rather than relying on the sea-level standard.
What is the difference between a nautical mile and a regular mile?
A statute (regular) mile is 5,280 feet or 1.609 km. A nautical mile is 6,076 feet or 1.852 km, which is about 15% longer. The nautical mile was defined to equal one minute of latitude, making it directly useful for navigation with charts. Knots measure nautical miles per hour, while mph measures statute miles per hour.
Why do some countries use km/h and others use mph?
Countries that adopted the metric system use km/h. The United States retained miles and mph from the British Imperial system. The UK itself partially metricated but kept mph for road signs. Historical adoption patterns, cost of changing road infrastructure, and cultural familiarity all play a role. Nearly all countries that have switched in recent decades moved from mph to km/h, never the reverse.
How do I convert between feet per second and mph?
Multiply ft/s by 0.6818 to get mph, or multiply mph by 1.4667 to get ft/s. For example, 88 ft/s equals 60 mph (this is a commonly referenced benchmark in physics and driver education). The ft/s unit is most often used in American engineering contexts, ballistics, and some older physics textbooks.
What speed is considered hypersonic?
Speeds above Mach 5 (approximately 3,836 mph or 6,174 km/h at sea level) are classified as hypersonic. At these velocities, air behaves differently due to extreme compression heating and chemical dissociation of gas molecules. Hypersonic research is active in military missile development and future civilian transport concepts. The fastest crewed aircraft, the X-15, reached Mach 6.7.
Can I convert negative speed values?
Yes. A negative value simply means motion in the opposite direction. The converter applies the same mathematical conversion regardless of sign. In physics, velocity is a vector quantity with both magnitude and direction, so negative values are meaningful in that context. The output will show negative values in all units when the input is negative.