How to avoid Unit conversion errors? Here's a simple trick

Can you imagine losing $125 million due to a little metric system error?

That’s exactly what happened in 1999 when NASA lost a Mars orbiter as one team used metric units for calculation and the other team didn’t.

But, this blog is not for showing you the output of wrong conversions. Rather it is to show you how to safely convert between units.

Ready?

The trick is to do the conversions as fractions.

Let's start with a simple example: Convert 3 km to m (3 kilometers to meters).

There are 1000 m in 1 km, so the conversion is easy, but let's follow a system.

• Write the conversion as a fraction that equals 1

• Multiply it out (leaving all units in the answer)

• Cancel any units that are both top and bottom

We can write the conversion as a fraction that equals 1: [1000 m / 1 km] = 1 And it is safe to multiply by 1 (does not affect the answer): 3 km × 1 = 3 km

So now we can do this: 3 km × [1000 m / 1 km] = 3000 km · m / 1 km

The answer looks strange! But we aren't finished yet. We can cancel any units that are both top and bottom: 3000 km · m / 1 km = 3000 m So, 3 km equals 3000 m. Well we already knew that, but we want to follow a system, so that when things get complicated (& they usually do) we know what to do!

Note: if you do it wrong (with the conversion upside down) you get this: 3 km × [1 km / 1000 m] = 3 km · km / 1000 m And that doesn't let us do any cancelling!

To avoid this mistake for larger calculations follow the system explained above!

To do it mentally, practice using it for complex calculations so that it gets wired in your brain.

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