Speed Converter: mph to km/h Driving Speed, Knots to km/h Marine Speed, Mach to km/h Flight Speed
Convert between meters per second, kilometers per hour, miles per hour, feet per second, knots, Mach and the speed of light. All equivalent speeds update in real time as you type; swap units in one tap, copy a converted value, or scan the full all-units summary. Covers road travel, sports, marine and aviation, and physics.
Speed conversion
Speed Convert
All units overview
All Units Overview
How to Use
Speed Converter Guide
m/s / km/h / mph / knots / Mach / light speed
The speed converter covers seven units spanning daily travel, marine/aviation and physics education: meters per second, kilometers per hour, miles per hour, feet per second, knots (nautical miles per hour), Mach and the speed of light. It is useful for road travel, sports tracking, sailing and flying, physics learning and engineering calculations. Enter any speed value to instantly convert all units, helping you switch between speed limits, sports data and scientific constants in different countries.
01 Common speed units
Kilometers per hour (km/h) is the standard road unit in China and most countries; 1 km/h = 1000 m / 3600 s ≈ 0.278 m/s. Meters per second (m/s) is the SI speed unit; 1 m/s = 3.6 km/h, commonly used in science. Miles per hour (mph) is mainly used in the US and UK; 1 mph ≈ 0.447 m/s ≈ 1.609 km/h — pay attention to the unit when driving in those countries.
The knot (kn) is the standard marine and aviation speed unit; 1 knot = 1 nautical mile/hour = 1852 m/h ≈ 0.514 m/s ≈ 1.852 km/h. Mach (Ma) is based on the speed of sound; 1 Mach ≈ 340.29 m/s at sea level and 20°C, while the actual value changes with temperature and altitude (about 295 m/s at 11,000 m). The speed of light (c) is the maximum speed of information in a vacuum, about 299,792,458 m/s — a physical constant used only in popular science and theory.
- 1 m/s = 3.6 km/h
- 1 km/h ≈ 0.6214 mph
- 1 mph ≈ 1.609 km/h
- 1 knot ≈ 1.852 km/h ≈ 0.514 m/s
- 1 Mach ≈ 340.29 m/s (sea level, 20°C)
- Light speed c ≈ 299,792,458 m/s
02 How to use
Enter a speed and choose the source unit (e.g. km/h); the right instantly shows the target (e.g. mph or knots), and the all-units overview lists all seven. When driving overseas, convert a speed limit from mph to km/h; for running, reference pace (min/km) against speed (km/h). Mach and light speed produce very large or small numbers and are shown in scientific notation automatically.
Inputs and actions
- value fieldEnter the numeric speed to convert; results update instantly.
- unit buttonsTap a unit to set it as source (left) or target (right); the active pair is highlighted.
- ⇄ SwapReverses the source and target units in one click.
- CopyCopies the full "X unit = Y unit" result to the clipboard.
- ResetRestores the default source/target units and value.
Output
- target resultThe converted speed in the selected target unit (read-only).
- rate tipShows the forward and reverse conversion factors.
- all unitsLists the value in all seven units at once; source is green, target blue.
- 1 m/s = 3.6 km/h is the most common speed conversion
- Knots are only for marine and aviation use; 1 knot = 1 nautical mile/hour
- Mach varies with altitude and temperature — about 295 m/s at 11,000 m
- Light speed is for a vacuum; it slows in a medium
- China’s highway speed limit is typically 120 km/h ≈ 75 mph
FinCompute’s free online speed converter covers meters per second, kilometers per hour, miles per hour, feet per second, knots, Mach and the speed of light — 7 units in one view. Whether you need mph to km/h for overseas driving, knots to km/h for marine speed, or Mach to km/h for fighter-jet flight speed, enter any value and see all results instantly.
Everyday driving speed: km/h, mph and m/s for physics
km/h is the road standard in China, Europe and most of the world; 1 m/s = 3.6 km/h. mph (miles per hour) is used in the US, UK and a handful of other countries; 1 mph ≈ 1.609 km/h. "How many km/h is 100 mph" and "how many mph is 100 km/h" are common overseas-driving questions, while km/h to m/s is a standard middle-school physics conversion.
Marine and aviation: knots to km/h for sailing and flight
1 knot (kn) = 1 nautical mile per hour = 1.852 km/h ≈ 0.514 m/s ≈ 1.151 mph. The nautical mile was historically defined as one minute of latitude, making knots directly tied to geographic coordinates — still the universal standard for ships and aircraft worldwide. "How many km/h is a knot" and "how many mph is a knot" are classic marine conversions.
Mach and light speed: fighter jets, astronomy and signal delay
Mach is the ratio of speed to the speed of sound. At sea level (20°C) Mach 1 ≈ 340.29 m/s ≈ 1,225 km/h ≈ 761 mph. "Mach to km/h" is a common query for fighter jets; the exact value varies with altitude — at 11,000 m cruise it drops to about 295 m/s (1,062 km/h). The speed of light c = 299,792,458 m/s in a vacuum, the cosmic speed limit used in astronomy and telecom signal-delay math.
Common speed conversions: driving, sailing, physics and aviation
Drivers compare speed limits between km/h (Europe/China) and mph (US/UK); runners convert pace from min/km to min/mile; sailors and pilots use knots exclusively; meteorologists convert wind speeds between km/h, mph and knots; physics students convert to m/s for kinetic energy equations; aerospace engineers reference Mach numbers; astronomers and telecom engineers reference light speed.
Speed conversion formulas: knot = 1852 m, light speed exact constant
m/s to km/h: km/h = m/s × 3.6. km/h to mph: mph = km/h ÷ 1.609344. mph to km/h: km/h = mph × 1.609344. Knots to km/h: km/h = kn × 1.852. m/s to knots: kn = m/s ÷ 0.514444. The knot is defined by international agreement as exactly 1 nautical mile per hour (1,852 m, adopted 1929); light speed has been an exact constant (299,792,458 m/s) since 1983.
Last updated: 2026-08-23
FAQ
QHow many km/h in 1 m/s?
1 m/s = 3.6 km/h exactly. To convert m/s to km/h, multiply by 3.6; to convert km/h to m/s, divide by 3.6.
QWhat is 100 km/h in mph?
100 km/h ÷ 1.609344 ≈ 62.14 mph. Conversely, 100 mph ≈ 160.9 km/h.
QWhat is a knot?
1 knot = 1 nautical mile per hour = 1.852 km/h ≈ 1.151 mph. Knots are used in marine and aviation navigation because the nautical mile corresponds to one minute of latitude.
QHow fast is Mach 1?
Mach 1 ≈ 340.29 m/s ≈ 1,225 km/h at sea level (20°C). At 11,000 m cruise altitude it is about 295 m/s (1,062 km/h) because sound travels slower in colder, thinner air.
QWhat is the speed of light?
In a vacuum c = 299,792,458 m/s ≈ 1.079 billion km/h ≈ 671 million mph. It takes about 8 minutes 20 seconds for sunlight to reach Earth, and about 1.3 seconds for a radio signal to reach the Moon.
QWhy do boats and planes use knots instead of km/h?
The nautical mile is based on Earth’s circumference (1 nautical mile = 1 minute of latitude), making distance and position calculations straightforward on nautical charts. One knot equals one nautical mile per hour, directly linking speed to navigational distance.
QWhat speed ranges are considered supersonic and hypersonic?
Subsonic: below Mach 1. Transonic: Mach 0.8–1.2. Supersonic: Mach 1–5. Hypersonic: above Mach 5. The SR-71 Blackbird reached about Mach 3.3; intercontinental ballistic missiles reach Mach 20+ during re-entry.
QHow fast is 60 mph in km/h?
60 mph × 1.609344 ≈ 96.6 km/h. Useful when driving in a country that uses km/h after seeing a mph speedometer; enter either value to see all speed units at once.
QHow many km/h is 20 knots?
20 knots × 1.852 = 37.04 km/h ≈ 23 mph. Sailors and pilots use knots worldwide because one knot equals one nautical mile per hour, tied directly to latitude on charts.
QHow many m/s is 100 km/h?
100 km/h ÷ 3.6 ≈ 27.78 m/s. This is the standard conversion used in physics problems and braking-distance calculations; m/s is the SI derived unit for speed.
QHow fast is Mach 2 in km/h?
Mach 2 at sea level ≈ 680.58 m/s ≈ 2,450 km/h ≈ 1,522 mph. Mach depends on air temperature and altitude, so the converter uses 340.29 m/s as the standard sea-level reference.
QHow many km/h is 100 mph?
100 mph × 1.609344 ≈ 160.9 km/h. Conversely, 100 km/h ≈ 62.14 mph — a handy pair for reading speed limits when driving between the US/UK and most of the rest of the world.
QHow many knots is 1 mph?
1 mph ≈ 0.869 knots. To convert knots to mph, multiply by 1.151; to convert mph to knots, multiply by 0.869. Sailboats and shipping always quote speed in knots because 1 knot = 1 nautical mile per hour.