Use a conversion table to determine the amount you have to multiply or divide the unit by when converting between units of measurement. Divide when moving up to a greater unit and multiply when moving down to a lesser one.
In general, conversions within the metric system are easier as units move up and down by multiples of ten. From small to large, milli-, centi- and deci- come before the unit name when indicating units smaller than the standard unit. For instance, a centimeter is 1/100 of a meter. Prefixes for larger units are deka-, hecto- and kilo-. Convert units up by dividing by 10, and down by multiplying by 10 for each step.
Using a unit conversion table, you can determine that you must multiply the amount you have in kilometers by 1000 to see its equivalent in meters. For instance, a 20 kilometer long path equals 20,000 meters.
Unlike the metric system, the imperial system does not follow a pattern. For instance, a foot equals .33 yards and a mile equals 1760 yards. Use the rates on a conversion table to convert imperial units to each other. For instance, to see the inch equivalent of a 5-yard long item, multiply the length by 36. By doing so, you find out that its length equals 180 inches.
You can also use unit conversion tables to convert the units of two systems to each other. The method is the exact same as moving up and down within either system. For instance, a mile equals 1.6 kilometers. As such, you multiply the amount in miles by 1.6 to see its equivalent in kilometers. A 300-mile long trip equals a 480-kilometer trip.