Speed converter

Which unit should you use?

km/h is the road standard almost everywhere outside the United States and the United Kingdom. mph covers the US, UK and a handful of others. Knots — one nautical mile per hour, or 1.852 km/h — are the standard at sea and in the air, because a nautical mile is one minute of latitude and therefore maps directly onto a chart. m/s is the SI unit and what you want for physics, engineering and wind measurements.

A useful shortcut: multiply m/s by 3.6 to get km/h, and divide km/h by 1.609 to get mph. For rough mental arithmetic, mph ≈ km/h × 0.6.

The table above is what the sign says. Your car’s speedometer reads a few percent higher than that, which is why a GPS reading looks slow next to it: see GPS speed vs your car speedometer.

km/h to mph

mph = km/h × 0.621371

km/h	mph
10	6.2
20	12.4
30	18.6
40	24.9
50	31.1
60	37.3
70	43.5
80	49.7
90	55.9
100	62.1
120	74.6
130	80.8

mph to km/h

km/h = mph × 1.609344

mph	km/h
10	16.1
20	32.2
30	48.3
40	64.4
50	80.5
55	88.5
60	96.6
65	104.6
70	112.7
75	120.7
80	128.7
100	160.9

Knots to km/h

km/h = knots × 1.852

Knots are the unit on every chart, radio and marine forecast. If that is new to you, start with knots for boating.

knots	km/h
1	1.9
5	9.3
10	18.5
15	27.8
18	33.3
20	37.0
25	46.3
30	55.6
40	74.1
50	92.6
60	111.1
100	185.2

km/h to knots

knots = km/h ÷ 1.852

km/h	knots
10	5.4
20	10.8
30	16.2
40	21.6
50	27.0
60	32.4
80	43.2
100	54.0
120	64.8
150	81.0
200	108.0
300	162.0

Knots to mph

mph = knots × 1.150779

knots	mph
1	1.2
5	5.8
10	11.5
15	17.3
18	20.7
20	23.0
25	28.8
30	34.5
40	46.0
50	57.5
60	69.0
100	115.1

m/s to km/h

km/h = m/s × 3.6

m/s	km/h
1	3.6
2	7.2
5	18.0
10	36.0
15	54.0
20	72.0
25	90.0
30	108.0
40	144.0
50	180.0
80	288.0
100	360.0

Need a live reading rather than a conversion? The GPS speedometer shows your actual speed in all four units.