Feb 14 2011

Converting Elevations in Your Head

Don’t you hate it when you’re looking at a topo map, or reading an article, and the elevations are in the wrong units? That would be meters if you’re an American, and feet for everyone else. We all know that the difference is roughly a factor of three, but it truly is a rough estimate. Wouldn’t it be nice to be more accurate without having to use a calculator? Here’s a method that yields an estimate to within 2% accuracy.

The actual, precise conversion numbers are 1.0 m = 3.2808399 ft OR 1 ft = 0.3048 m. But you can get close enough by doing the following.


Meters to Feet
Step 1: Take the value in meters and divide by 3.
Step 2: Multiply that value by 10.

Mathematically this is the same as multiplying by 3.333 (10/3), which is close enough to 3.28 for estimating purposes.


Feet to Meters
Step 1: Divide the elevation in feet by 10
Step 2: Multiply that value by 3

Mathematically this is the same as multiplying the elevation by 0.3, again, close enough to 0.3048 for estimating purposes.



Deriving the Precise Conversion Factor
The actual conversion ratio is easy to determine if you remember three relationships. Two are common knowledge; 1) there are 100 cm per meter, and 2) there are 12 inches per foot. The crux data is: 1.0 inch equals 2.54 centimeters

1 in = 2.54 cm, 1 ft = 12 in, 1 m = 100 cm

From these the following mathematical equality can be derived, and thus an accurate conversion number.

1m/100cm X 2.54cm/in X 12in/ft = 0.3048 m / ft –OR- 3.2808399 ft / m

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