MPH to KM/H Converter

miles per hour to kilometers per hour — quick reference

The formula, worked line by line

Since 1959 the international yard has been fixed at exactly 0.9144 metres, which makes the foot exactly 0.3048 m and the mile, at 5,280 feet, exactly 1,609.344 metres or 1.609344 km. Speed inherits that factor unchanged, because the hour on the left of the conversion is the same hour on the right. Nothing cancels, nothing compounds: a rate built from an exactly defined distance over an identically defined time converts with the distance factor alone.

km/h = mph × 1.609344
mph  = km/h ÷ 1.609344   (the reverse)
     = km/h × 0.6213712…
70 mph → 70 × 1.609344 = 112.65408 km/h

The multiply-by-1.6 shortcut is the rare mental trick that is genuinely accurate. It runs 0.58 percent low, about half a km/h at highway speed and just under a full km/h at 100 mph. Since it always errs low, it is the cautious direction to be wrong in when you are judging yourself against a posted limit.

The factor itself carries no error at all, so any discrepancy you see between this tool and another comes from rounding the display, not from the conversion.

How to use the MPH to KM/H converter

The moment this conversion matters is the first mile out of the rental lot in Ireland, France, Mexico, or Canada. The dashboard needle is reading km/h, the sign ahead says 100, and the only speed you actually have a feel for is the mph you drive at home. Enter the mph you know and this converter gives you the metric number you will be measured against; Swap flips it when you want to read the sign instead.

The factor behind it is exact rather than approximate, because the mile has been defined as exactly 1,609.344 metres since 1959, so nothing here is rounded except the display. That matters less at 30 mph than at 85, but it costs nothing to have the exact number rather than a rule of thumb.

The most useful thing to do before you drive is memorise your own limits in metric, and the chart below is that list. Push one step further and 85 mph, the highest posted limit in the United States on a stretch of tollway outside Austin, Texas, is 136.8 km/h, which is faster than any general motorway limit in Europe including the 140 km/h that Poland posts on its autostrada network.

Around town the gap runs the other way and feels bigger than it is. A 50 km/h built-up default, which is what Ireland, France, Italy, Germany, Poland and the Netherlands all use, is 31.1 mph. A 30 km/h zone is 18.6 mph, slower than most US neighbourhood driving, and Wales dropped its own built-up default to 20 mph in September 2023, which is 32.2 km/h.

Is multiplying by 1.6 close enough to drive on?

For quick mental work, multiply mph by 1.6. It reads 0.58 percent low, which is nothing on a road: 60 mph gives 96 against a true 96.6, and 75 mph gives 120 against 120.7. The error only becomes visible at speed, where 100 mph gives 160 against a true 160.9.

Because the shortcut always errs low, it flatters you slightly when you are checking yourself against a limit, so lean on the exact factor when a number has to be defensible. One more thing worth knowing before you trust any dial: under UN Regulation 39, which EU and UK type approval follows, an indicated speed must never be less than the true speed and may exceed it by up to 10 percent plus 4 km/h.

Every miles per hour value, worked out

78 common miles per hour figures each get their own page, with the answer at full precision, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Questions people ask