The Quick and Dirty

via jitze/Flickr

by Math Dude

Have you ever needed to convert from miles to kilometers or vice versa? Perhaps you’re from the US and you were traveling in Europe. Or maybe you use kilometers at home and you were traveling in the US. Either way, it can be confusing. But the good news is that it’s easy to do the unit conversion in your head…and this post contains everything you need to know.

To convert distances in miles into distances in kilometers (or speeds in miles per hour into speeds in kilometers per hour), simply multiply the number of miles by 1.6 (which, completely coincidentally, turns out to be close to the value of the golden ratio that comes from the Fibonacci sequence):

(distance in kilometers) ≈ 1.6 * (distance in miles)

So, if you need to find the approximate number of kilometers in 10 miles, just multiply 10 by 1.6 to find that 10 miles is 1.6 * 10 ≈ 16 kilometers. And you can use this same formula to convert speeds. To find what 50 miles per hour is in kilometers per hour, multiply 50 by 1.6 to find that 50 miles per hour is 1.6 * 50 ≈ 80 kilometers per hour.

Need to go from kilometers to miles instead? No problem. We can use a bit of basic algebra to turn our conversion around:

(distance in miles) ≈ 0.6 * (distance in kilometers)

How many miles are in 100 kilometers? Just multiply those 100 kilometers by 0.6 to find that 100 kilometers ≈ 60 miles. What’s 50 kilometers per hour in miles per hour? Just multiply 50 by 0.6 to find that 50 kilometers per hour ≈ 30 miles per hour. That’s it!

To sum up, just remember these two things:

• Distances in kilometers are always 60% larger than distances in miles (so multiply miles by 1.6);
• Distances in miles are always 60% of distances in kilometers (so multiply kilometers by 0.6).