Widely used units in the SI system
A list of the widely used units in the SI system is provided in the table.
| unit | abbreviation | physical quantity | ||
|---|---|---|---|---|
| Base units | metre | m | length | |
| second | s | time | ||
| kilogram | kg | mass | ||
| ampere | A | electric current | ||
| kelvin | K | thermodynamic temperature | ||
| candela | cd | luminous intensity | ||
| mole | mol | amount of substance | ||
| unit | abbreviation | number of metres | approximate U.S. equivalent | |
| Length | kilometre | km | 1,000 | 0.62 mile |
| centimetre | cm | 0.01 | 0.39 inch | |
| millimetre | mm | 0.001 | 0.039 inch | |
| micrometre | μm | 0.000001 | 0.000039 inch | |
| nanometre | nm | 0.000000001 | 0.000000039 inch | |
| unit | abbreviation | number of square metres | approximate U.S. equivalent | |
| Area | square kilometre | sq km, or km2 | 1,000,000 | 0.3861 square mile |
| hectare | ha | 10,000 | 2.47 acres | |
| are | a | 100 | 119.60 square yards | |
| square centimetre | sq cm, or cm2 | 0.0001 | 0.155 square inch | |
| unit | abbreviation | number of cubic metres | approximate U.S. equivalent | |
| Volume | cubic metre | m3 | 1 | 1.307 cubic yards |
| cubic centimetre | cu cm, cm3, or cc | 0.000001 | 0.061 cubic inch | |
| unit | abbreviation | number of litres | approximate U.S. equivalent | |
| Capacity | kilolitre | kl | 1,000 | 1.31 cubic yards |
| litre | l | 1 | 61.02 cubic inches | |
| centilitre | cl | 0.01 | 0.61 cubic inch | |
| millilitre | ml | 0.001 | 0.061 cubic inch | |
| microlitre | μl | 0.000001 | 0.000061 cubic inch | |
| unit | abbreviation | number of grams | approximate U.S. equivalent | |
| Mass and weight | metric ton | t | 1,000,000 | 1.102 short tons |
| gram | g | 1 | 0.035 ounce | |
| centigram | cg | 0.01 | 0.154 grain | |
| milligram | mg | 0.001 | 0.015 grain | |
| microgram | μg | 0.000001 | 0.000015 grain | |
| unit | symbol | physical quantity | expressed in base units | |
| Energy | hertz | Hz | frequency | 1/s |
| newton | N | force, weight | (m × kg)/s2 | |
| joule | J | work, energy, quantity of heat | (m2 × kg)/s2 | |
| pascal | Pa | pressure, stress | kg/(m × s2) | |
| watt | W | power | (m2 × kg)/s3 | |
| coulomb | C | electric charge | s × A | |
| volt | V | electric potential difference | (m2 × kg)/(s3 × A) | |
| farad | F | electric capacitance | (s2 × s2 × A2)/(m2 × kg) | |
| ohm | Ω | electric resistance, reactance | (m2 × kg)/(s3 × A2) | |
| siemens | S | electric conductance | (s3 × A2)/(m2 × kg) | |
| weber | Wb | magnetic flux | (m2 × kg)/(s2 × A) | |
| tesla | T | magnetic induction | kg/(s2 × A) | |
| henry | H | inductance | (m2 × kg)/(s2 × A2) | |
| lumen | lm | luminous flux | cd × sr | |
| lux | lx | illuminance | (cd × sr)/m2 | |
Prefixes and units used in the metric system
Prefixes and units used in the metric system are provided in the table.
| physical quantity | unit | symbol | ||||
|---|---|---|---|---|---|---|
| *The metric system of bases and prefixes has been applied to many other units, such as decibel (0.1 bel), kilowatt (1,000 watts), megahertz (1,000,000 hertz), and microhm (one-millionth of an ohm). | ||||||
| Base units* | length | metre | m | |||
| area | square metre | square m, or m2 | ||||
| are (100 square metres) | a | |||||
| volume | cubic metre | cubic m, or m3 | ||||
| stere (1 cubic metre) | s | |||||
| weight | gram | g | ||||
| metric ton (1,000,000 grams) | t | |||||
| capacity | litre | l | ||||
| temperature | degree Celsius | °C | ||||
| prefix | symbol | factor by which base unit is multiplied | example | |||
| Prefixes designating multiples and submultiples* | exa- | E | 1018 | = | 1,000,000,000,000,000,000 | |
| peta- | P | 1015 | = | 1,000,000,000,000,000 | ||
| tera- | T | 1012 | = | 1,000,000,000,000 | ||
| giga- | G | 109 | = | 1,000,000,000 | ||
| mega- | M | 106 | = | 1,000,000 | megaton (Mt) | |
| kilo- | k | 103 | = | 1,000 | kilometre (km) | |
| hecto-, hect- | h | 102 | = | 100 | hectare (ha) | |
| deca-, dec- | da | 10 | = | 10 | decastere (das) | |
| 1 | ||||||
| deci- | d | 10−1 | = | 0.1 | decigram (dg) | |
| centi-, cent- | c | 10−2 | = | 0.01 | centimetre (cm) | |
| milli- | m | 10−3 | = | 0.001 | millilitre (ml) | |
| micro-, micr- | μ | 10−6 | = | 0.000001 | microgram (μg) | |
| nano- | n | 10−9 | = | 0.000000001 | ||
| pico- | p | 10−12 | = | 0.000000000001 | ||
| femto- | f | 10−15 | = | 0.000000000000001 | ||
| atto- | a | 10−18 | = | 0.000000000000000001 | ||
Metric conversions
A list of metric conversions is provided in the table.
| approximate common equivalents | |
|---|---|
| *Common term not used in SI. | |
| **Exact. | |
| Source: National Bureau of Standards Wall Chart. | |
| 1 inch | = 25 millimetres |
| 1 foot | = 0.3 metre |
| 1 yard | = 0.9 metre |
| 1 mile | = 1.6 kilometres |
| 1 square inch | = 6.5 square centimetres |
| 1 square foot | = 0.09 square metre |
| 1 square yard | = 0.8 square metre |
| 1 acre | = 0.4 hectare* |
| 1 cubic inch | = 16 cubic centimetres |
| 1 cubic foot | = 0.03 cubic metre |
| 1 cubic yard | = 0.8 cubic metre |
| 1 quart (liq) | = 1 litre* |
| 1 gallon | = 0.004 cubic metre |
| 1 ounce (avdp) | = 28 grams |
| 1 pound (avdp) | = 0.45 kilogram |
| 1 horsepower | = 0.75 kilowatt |
| 1 millimetre | = 0.04 inch |
| 1 metre | = 3.3 feet |
| 1 metre | = 1.1 yards |
| 1 kilometre | = 0.6 mile (statute) |
| 1 square centimetre | = 0.16 square inch |
| 1 square metre | = 11 square feet |
| 1 square metre | = 1.2 square yards |
| 1 hectare* | = 2.5 acres |
| 1 cubic centimetre | = 0.06 cubic inch |
| 1 cubic metre | = 35 cubic feet |
| 1 cubic metre | = 1.3 cubic yards |
| 1 litre* | = 1 quart (liq) |
| 1 cubic metre | = 264 gallons |
| 1 gram | = 0.035 ounce (avdp) |
| 1 kilogram | = 2.2 pounds (avdp) |
| 1 kilowatt | = 1.3 horsepower |
| conversions accurate within 10 parts per million | |
| inches × 25.4** | = millimetres |
| feet × 0.3048** | = metres |
| yards × 0.9144** | = metres |
| miles × 1.60934 | = kilometres |
| square inches × 6.4516** | = square centimetres |
| square feet × 0.0929030 | = square metres |
| square yards × 0.836127 | = square metres |
| acres × 0.404686 | = hectares |
| cubic inches × 16.3871 | = cubic centimetres |
| cubic feet × 0.0283168 | = cubic metres |
| cubic yards × 0.764555 | = cubic metres |
| quarts (liq) × 0.946353 | = litres |
| gallons × 0.00378541 | = cubic metres |
| ounces (avdp) × 28.3495 | = grams |
| pounds (avdp) × 0.453592 | = kilograms |
| horsepower × 0.745700 | = kilowatts |
| millimetres × 0.0393701 | = inches |
| metres × 3.28084 | = feet |
| metres × 1.09361 | = yards |
| kilometres × 0.621371 | = miles (statute) |
| square centimetres × 0.155000 | = square inches |
| square metres × 10.7639 | = square feet |
| square metres × 1.19599 | = square yards |
| hectares × 2.47105 | = acres |
| cubic centimetres × 0.0610237 | = cubic inches |
| cubic metres × 35.3147 | = cubic feet |
| cubic metres × 1.30795 | = cubic yards |
| litres × 1.05669 | = quarts (liq) |
| cubic metres × 264.172 | = gallons |
| grams × 0.0352740 | = ounces (avdp) |
| kilograms × 2.20462 | = pounds (avdp) |
| kilowatts × 1.34102 | = horsepower |