Most jobs require that you work in either English units or Metric units, but usually not both.  It may be necessary, however, on occasion to convert units from one system to another.
wrenchguy
Metric to English
English to Metric
Length:
1millimeter (m) = 0.04 inches (in)
1 centimeter (cm) = 0.39 inches (in)
1 meter (m) = 39.37 inches = 3.28 feet (ft)
1 meter (m) = 1.09 yard (yd)
1 kilometer (km) = 0.62 miles (mi)
Length:
1 inch (in) = 2.54 centimeters (cm)
1 foot (ft) = 30.48 cm = 0.305 meters (m)
1 yard (yd) = 0.914 meters (m)
1 mile (mi) = 1.609 kilometer (km)
Weight:
1 gram (g) = 0.035 ounces (oz)
1 liter (l) = 1.057 quart (qt)
Weight:
1 ounces (oz) = 28.350 grams (g)
1 pound (lb) = 0.453 kilograms (kg)
Capacity:
1 milliliter (ml) = 0.2 teaspoon (tsp)
1 liter (l) = 1.057 quart (qt)
Capacity:
1 teaspoon (tsp) = 5 milliliters (ml)
1 cup (c) = 236 milliliters (ml)
1 quart (qt) = 0.9461 liter (l)
1 gallon (gal) = 3.785 liter (l)

 

Let's take a look at some conversions between systems
using dimensional analysis:

expin1
Convert 155 cm to feet.

Between systems: (round to nearest hundreth))
1 inch = 2.54 cm
Notice the need for 2 conversion ratios (both of which equal 1).
All units cancel out except for the desired units.
cmtofeet

 

expin2
Convert 12 yards to centimeters.
Between systems.
Notice the need for 2 conversion ratios (both of which equal 1).
All units cancel out except for the desired units.
bm5

 

expin3
Convert 120 km per hour to
miles per minute.
Between systems. (round to 3 decimal places)
Notice the need for 2 conversion ratios (both of which equal 1).
All units cancel out except for the desired units.
milesperminute

 

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