Speed Converter — km/h, mph, m/s, Knots & More

Multiply by 0.6 for a rough answer, or more precisely by 0.621. So 100 km/h ≈ 60 mph (exact: 62.1), 80 km/h ≈ 50 mph (exact: 49.7). The "multiply by 5 and divide by 8" trick also works: 80 × 5 ÷ 8 = 50 mph.

100 km/h = 62.14 mph. This is a common highway speed in metric countries. For US drivers visiting Europe: 60 mph ≈ 96.6 km/h, 65 mph ≈ 105 km/h, 75 mph ≈ 121 km/h.

1 knot = 1 nautical mile per hour = 1.852 km/h = 1.151 mph. The name comes from the old practice of throwing a knotted rope off a ship's stern and counting how many knots passed through your hands in a fixed time — that told you your speed. Aviation and shipping still use knots today because they relate directly to degrees of latitude on a chart.

At sea level (15°C / 59°F), sound travels at 343 m/s = 1,235 km/h = 767 mph = 661 knots. At cruising altitude (cold and thin air), it's closer to 295 m/s = 1,062 km/h. "Mach 1" means you're moving at the speed of sound; "Mach 2" is twice that.

Multiply by 3.6. The logic: 1 m/s means 1 meter every second, which is 3,600 meters per hour, which is 3.6 km/h. So 10 m/s = 36 km/h, 25 m/s = 90 km/h. To go the other way, divide by 3.6.

Bolt's peak speed during his 100m world record was about 44.7 km/h (27.8 mph, 12.4 m/s). His average speed for the whole 100m was around 37.6 km/h. For comparison, a decent amateur cyclist on a flat road can sustain ~25–30 km/h.

Speed is how fast you're going (a number). Velocity is speed in a specific direction (a number plus a direction). In everyday use, we use them interchangeably. In physics, they're distinct: a car going around a circular track at constant speed is constantly changing velocity because direction keeps changing.