MathBench > Measurement

The Size of Things

Metric conversions: step to the right, step to the left

First, the basics. One meter (which is oddly enough just about the same size as a meter stick) can be divided into 1000 parts called millimeters.

So, if I want to convert a measurement in millimeters to one in meters, I can do it by moving the decimal point 3 places to the left:

277 mm -> 0.277 m

Likewise, if I want to convert a measurement in meters to one in millimeters, I can do it by moving the decimal point 3 places to the right:

0.341 m -> 341 mm

If you don't have any decimal places to move to the right, then you need to add zeros:

345 m ->345000 mm

34.5 m ->34500 mm

A lot of people remember the part about moving the decimal point over by 3, but donít remember whether it goes to the left or the right. Thereís an easy solution for this: make sure your answer makes sense! Millimeters are pretty small. Itís going to take MORE millimeters than meters to make the same measurement.

A few big units = Lots of small units

skeletonIf you convert the length of your finger (70 millimeters) into 70,000 meters, stop and think a moment. 70,000 meters is pretty ridiculous. Donít pull a Paul Bunyan. (And believe me, at least one student does something similar on an exam every semester. Donít let it be you!)

Hereís the part they donít do in grade school: if you divide a millimeter into 1000 pieces, you get a micrometer, abbreviated µm, or um (being easier to type on a standard keyboard).

And if you divide a um into 1000 pieces, you get a nanometer, or nm.

So altogether now: