Some basic formulas can help convert different units from metric to US and vice versa.
Inches - centimeters
For example, there are 2.54 centimeters in an inch. So to convert inches to centimeters, multiply by 2.54 (ie, 10 inches x 2.54 centimeters/inch = 25.4 centimeters). To convert centimeters to inches, divide by 2.54 instead of multiplying (ie, 10 centimeters/2.54 = 3.937 inches).
Miles - kilometers
For miles and kilometers, use the fact that one kilometer equals 0.62 miles (actually, 0.62137 miles). So multiply by 0.62 to go from kilometers to miles (ie, 10 kilometers x 0.62 miles/kilometer = 6.2 miles). To change from miles into kilometers, divide by 0.62 (ie, 10 miles/0.62 = 16.13 (about) kilometers).
Pounds - kilograms
With weight, you convert units by knowing there are about 2.2 pounds (actually, closer to 2.2046 pounds) in one kilogram. So to convert from kilograms to pounds, multiply by 2.2 (ie, 5 kilograms x 2.2 pounds/kilogram = 11 pounds). To convert from pounds to kilograms, divide by 2.2 (ie, 5 pounds/2.2 = 2.272 kilograms).
Fahrenheit - Celsius
Finally, for temperatures, you need to know that 1 degree Celsius = 9/5 degree Fahrenheit. And, because 0 degrees Celsius is actually 32 degrees Fahrenheit, you also need to add or subtract 32 to go from one measure to the other. For example, to convert from Fahrenheit to Celsius, first subtract 32 and then multiply the resulting number by 5/9. (Technically, you're dividing by 9/5 (degrees Fahrenheit per degree Celsius), but that's the same as multiplying by 5/9). So you get 92 degrees Fahrenheit - 32 = 60, then multiply 60 x 5/9 = 33.33 degrees Celsius. To convert from Celsius to Fahrenheit, first multiply by 9/5, then add 32: 25 degrees Celsius x 9/5 = 45, then add 32 to 45 = 77 degrees Fahrenheit.
To sum up:
- inches to centimeters - multiply by 2.54
- centimeters to inches - divide by 2.54
- miles to kilometers - divide by 0.62
- kilometers to miles - multiply by 0.62
- pounds to kilograms - divide by 2.2
- kilograms to pounds - multiply by 2.2
- Celsius to Fahrenheit - multiply by 9/5 then add 32
- Fahrenheit to Celsium - subtract 32 then multiply by 5/9