How to convert kilometers to miles (and back again)
Today we're going to take a look at how to convert between kilometers and miles, and back again. We'll take you through some tips for how to manually calculate the figures in your head, plus we'll give you a converter so that you can check your answers (you can skip straight to the conversion tool if you want to). Let's begin.
The standard 'converter' approach applied to the common problem of turning, say, 144 kilometres into miles would require you to remember that one km equals 0.62137119 miles and being able to multiply that by 144 in your head. Well, good luck with that. Rain Man might be able to do it. I certainly can't.
What I can do is to remember that, more sensibly, five miles equals eight kilometres and to use a trick an uncle taught me on an early drive through France.
You take the kilometre number, 144, and halve it; 72. Then take a quarter of your half, 18, and just add the two together. 72 + 18 = 90. That's your answer in miles.
What about going the other way, for the European traveller trying to convert those weird miles into nice neat kilometres? Well, the obvious way is to divide by five and then multiply by eight. 90 ÷ 5 = 18 x 8 = 144.
So, yes, of course it works but there's a problem; While dividing by five is easy enough (divide by ten and double it), multiplying by eight is trickier. One way to solve it is to reduce the principal number to something that appears in the eight times table then convert it back. So that 18 could be halved to nine and we all remember, don't we, that nine eights are 72. Double back again and we get to 144.
How to estimate on the move
As an alternative, let's think about about a kilometre equalling (roughly) six tenths of a mile. This is why British and American soldiers stationed in Germany were taught an 'on manoeuvres' converter: divide the miles by six and move the decimal point one point to the right.
Let's try it. Six goes into 90 fifteen times. Express that as 15.0 and move the decimal point one place right and arrive at 150. You can also divide by three and multiply by five: 90 ÷ 3 = 30 x 5 = 150. Pretty close (but I hope they don't use it for calculating artillery ranges).
Again, though, there's a formula that's almost as easy to work out in your head but delivers a precise result. Divide the number of miles by five and subtract that from the original. Then double the resulting number. So:
1 km: 0.62137119 mi
1 mile: 1.609344 km
90 miles ÷ 5 = 18.
90 - 18 = 72.
72 x 2 = 144 kilometers.
That'll do nicely. Did you see what we did there? Turned the miles number into four fifths and then doubled it to make eight fifths, or the reverse of five eighths. Sometimes fractions are easier than decimals.
Of course, if you're looking for a pain-free method of doing the calculation right here and now then you can use our handy kilometers and miles converter, below.
Kilometers to miles converter
For future reference, the regular miles and kilometers conversion tool is here. You'll be happy to hear that this website provides a comprehensive list of online conversion tools. So, should you wish to convert between kilometers, miles and any other units of distance, give the length and distance converter a try.
Written by Nick Valentine
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Last update: 18 July 2016
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