Speed Converter

Multiply by 1.609344. Sixty mph is 96.6 km/h, and a useful mental approximation is to add 60% — 60 plus 36 is 96.

One nautical mile per hour, where a nautical mile is exactly 1,852 metres. It is about 1.15 mph, and it is used at sea and in aviation because it relates directly to latitude.

Because it is a ratio to the local speed of sound, which falls with temperature. Mach 1 is about 1,225 km/h at sea level and about 1,062 km/h in the cold air at cruising altitude.

Multiply by 3.6, which is 3,600 seconds per hour divided by 1,000 metres per kilometre. It is one of the few conversions worth memorising outright.

Around 10.4 m/s over a short measured stretch, which is about 37 km/h or 23 mph. Sustained marathon pace is roughly a fifth of that.

Exactly 299,792,458 metres per second — a defined value, because the metre is now defined in terms of it rather than the other way round.

The speed at which drag balances weight and acceleration stops. For a human it is around 200 km/h belly-down and considerably higher head-down.

About 343 m/s in air at 20 °C, and it rises with temperature. It travels several times faster in water and faster again in steel.

Speed is a magnitude; velocity includes direction. An object moving in a circle at constant speed has continuously changing velocity, which is why it accelerates.

Add 60%: 50 mph is 50 + 30 = 80 km/h, against the true 80.5. Going the other way, subtract 40% — a rougher approximation.

Because one nautical mile is one minute of latitude, so speeds and distances relate directly to chart coordinates. It survives from marine navigation for the same reason.

Airspeed is relative to the air; ground speed includes the wind. A headwind can reduce ground speed dramatically while airspeed is unchanged, which is why flight times differ by direction.