Miles per Hour to Kilometers per Hour Converter

If you think in km/h, a speed posted in mph is hard to judge by feel. These are common values, rounded to two decimals:

A rental car in an mph country will have an mph speedometer, so you won't need to convert while driving. Where the table helps is in judging the speed: 70 mph is a little over 112 km/h, not 70-something.

Multiplying by 1.6, which is adding 60%, gives 112 km/h for 70 mph. That is 0.58% low against the converter's 112.65, and the error is the same at any speed.

A trick that needs no multiplication uses neighbouring Fibonacci numbers, whose ratio sits close to 1.618, near the true factor of 1.609:

• 5 mph ≈ 8 km/h (true: 8.05)
• 8 mph ≈ 13 km/h (true: 12.87)
• 13 mph ≈ 21 km/h (true: 20.92)
• 21 mph ≈ 34 km/h (true: 33.80)
• 34 mph ≈ 55 km/h (true: 54.72)

Break other speeds into these pieces. 50 mph is 21 + 21 + 8, so it is about 34 + 34 + 13 = 81 km/h. The converter says 80.47, so the estimate is 0.66% high.

Gym treadmills often run in mph. A setting of 6 mph is 9.6561 km/h, and 4 mph, a brisk walk for many people, is 6.4374 km/h.

An mph setting converts neatly to pace per mile: 60 ÷ 6 = 10, so 6 mph is a 10:00 mile. For pace per kilometer, divide 60 by the km/h figure instead. 60 ÷ 9.6561 is 6.2137 minutes, which is about 6:13 per km.

Car acceleration. 60 mph is 96.56 km/h, a little under 100. A car's 0–60 mph time is therefore slightly shorter than its 0–100 km/h time, so don't compare the two figures as if they were the same test.

Weather. A forecast gust of 30 mph is 48.28 km/h.

Sports. Pitch and serve speeds are often quoted in mph. A 90 mph pitch or serve is 144.84 km/h.