A chart to look up a conversion factor and do the math by hand. To convert, multiply by the factor in the row that matches the direction you’re going:
Factors marked exact are defined values; the rest are rounded to six significant figures, which is more than enough for schoolwork.
Metric Prefixes
| Prefix | Symbol | Multiplier |
|---|---|---|
| giga- | G | (1,000,000,000) |
| mega- | M | (1,000,000) |
| kilo- | k | (1,000) |
| hecto- | h | (100) |
| deka- | da | (10) |
| (base unit) | 1 | |
| deci- | d | (0.1) |
| centi- | c | (0.01) |
| milli- | m | (0.001) |
| micro- | µ | (0.000001) |
| nano- | n | (0.000000001) |
A kilometer is 1,000 meters, a centimeter is 0.01 meters, and a milligram is 0.001 grams.
Length
| From | To | Multiply by |
|---|---|---|
| inches | centimeters | 2.54 (exact) |
| feet | meters | 0.3048 (exact) |
| yards | meters | 0.9144 (exact) |
| miles | kilometers | 1.609344 (exact) |
| centimeters | inches | 0.393701 |
| meters | feet | 3.28084 |
| kilometers | miles | 0.621371 |
Mass
| From | To | Multiply by |
|---|---|---|
| pounds | kilograms | 0.45359237 (exact) |
| ounces | grams | 28.3495 |
| kilograms | pounds | 2.20462 |
| grams | ounces | 0.0352740 |
Volume
| From | To | Multiply by |
|---|---|---|
| US gallons | liters | 3.785411784 (exact) |
| US quarts | liters | 0.946353 |
| US cups | milliliters | 236.588 |
| US fluid ounces | milliliters | 29.5735 |
| liters | US gallons | 0.264172 |
| milliliters | US fluid ounces | 0.0338140 |
Area and Speed
| From | To | Multiply by |
|---|---|---|
| square feet | square meters | 0.09290304 (exact) |
| acres | hectares | 0.404686 |
| square miles | square kilometers | 2.58999 |
| miles per hour | kilometers per hour | 1.609344 (exact) |
| kilometers per hour | miles per hour | 0.621371 |
| meters per second | kilometers per hour | 3.6 (exact) |
Temperature
Temperature scales don’t share a zero point, so they need a formula instead of a single factor:
Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea level. Normal body temperature is about 37 °C (98.6 °F).
Exact vs. Rounded Factors
Several conversions are exact by definition: the inch is exactly 2.54 cm, the pound exactly 0.45359237 kg, and the US gallon exactly 3.785411784 L. Their reverses (like meters to feet) are not, because dividing by an exact factor gives a number that never ends, so those are rounded. Keep at least as many significant figures in the factor as in your measurement, and round only your final answer.