Convert your length or distance, if it is in imperial units, to metric units. Use the following formulas as a guide:
1 millimeter (mm) = 0.0394 inches (in)
1 meter (m) = 3.28 feet (ft) = 39.4 in = 1.1 yards (yd)
1 kilometer (km) = 0.621 miles (mi)
Learn the chronological order of the prefixes used for all metric units; in terms of length, each prefix is followed by the suffix "meter." In chronological order, from largest to smallest, the prefixes include kilo, hecto, deka, [unit---no prefix], deci, centi and milli. Thus, in the case of length/distance, the metric units would be: kilometer, hectometer, dekameter, meter, decimeter, centimeter and millimeter. Form a mnemonic, such as Purple Math's "King Henry Doesn't Usually Drink Chocolate Milk," to remember the order of the prefixes.
Convert from one unit to the other by counting the number of prefixes you move from. For example, if you are converting from kilometers to dekameters, you are moving two spaces; if you are converting from meters to kilometers, you are moving three spaces.
Multiply by 10 each time you move spaces to the right; divide by 10 each time you move spaces to the left. Another way to look at it is to move the decimal place the same amount of spaces, to the left or right, as you are moving between the prefixes. For example, converting 1.2 kilometers to dekameters involves moving two prefix spaces to the right. This means multiplying 1.2 by 10^2, which is 100, or moving the decimal place twice to the right, to get 120 dekameters (dam). If converting 456 mm to meters, it involves moving three prefix spots to the left, or dividing 456 by 10^3, which is 1,000, or moving the decimal spot three times to the left to get 0.456 meters (m).