The International System of Units (SI) is the modern form of the metric system. It is the only system of measurement with an official status in nearly every country in the world.
Also Read: List of Important Scientific Instruments
It comprises a coherent system of units of measurement starting with seven base units as listed below:
INTERNATIONAL UNITS
| S.No. | Base unit | Symbol | Year of Adoption |
|---|---|---|---|
| 1 | METRE – Unit of length | m | 1960 |
| 2 | KILOGRAM – Unit of mass | kg | 1960 |
| 3 | SECOND – Unit of time | s | 1967 |
| 4 | AMPERE – Unit of electric current | A | 1948 |
| 5 | KELVIN – Unit of thermodynamic temperature | K | 1967 |
| 6 | CANDELA – Unit of luminous intensity | cd | 1967 |
| 7 | MOLE – Amount of substance* | mol | 1971 |
- *One mole (mol) is an amount substance in grams equal to its molecular weight.
- *In 1971 the US decided to change over to the Metric System in ten years at the end of which the US will be predominantly but not exclusively on the Metric System. The Metric Conversion Act of 1975 legalized the change-over and set up the US Metric Board to supervise it.
S.I. EQUIVALENTS
The SI is intended to be an evolving system; units and prefixes are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves.
| LENGTH | |
| 1 | 1 angstrom = 0.1 nanometre (mm) |
| 2 | 1 chain = 20.12 metre (m) |
| 3 | 1 engineer’s chain = 30.48 metre (m) |
| 4 | 1 fathom = 1.829 metre (m) |
| 5 | 1 foot = 0.3048+ metre (m) |
| 6 | 1 furlong = 0.2012+ Kilometre (km) |
| 7 | 1 inch = 25.4 milimetre (mm) |
| 8 | 1 link = 0.2012+ metre(m) |
| 9 | 1 mile = 1.609 Kilometre (km) |
| 10 | 1 nautical mile international = 1.852 Kilometre (km) |
| 11 | 1 nautical mile telegraph = 1.855 Kilometre (km) |
| 12 | 1 nautical mile U.K. = 1.853 Kilometre (km) |
| AREA | |
| 13 | 1 acre = 4047 sq metre |
| 14 | 1 sq foot = 929.0 sq centimetre |
| 15 | 1 sq mile = 2.599 sq kilometre |
| 16 | 1 sq yard = 0.8361+ sq metre |
| VOLUME | |
| 17 | 1 cubic foot = 28.32 cubic decimetre |
| 18 | 1 cubic inch = 16.39 cubic centimetre |
| 19 | 1 fluid ounce = 28.41 cubic centimetre |
| 20 | 1 gallon, imperial = 4.546 cubic decimetre |
| 21 | 1 gallon US = 3.785 cubic decimetre |
| 22 | 1 pint, imperial = 0.5863+ cubic decimetre |
| MASS | |
| 23 | 1 grain = 64.80 miligram |
| 24 | 1 hundred weight = 50.80 kilogram |
| 25 | 1 maund = 37.32 kilogram |
| 26 | 1 ounce = 28.35 gram |
| 27 | 1 pound = 0.4536+ kilogram |
| 28 | 1 quintal = 100 kilogram |
| 29 | 1 seer = 0.9331+ kilogram |
| 30 | 1 tola = 11.66 gram |
| 31 | 1 ton = 1.016 tonne |
| 32 | 1 ton US = 0.9072+ tonne |
| VELOCITY | |
| 33 | 1 foot per minute = 0.00508+ metre per second |
| 34 | 1 foot per second = 0.3048+ metre per second |
| 35 | 1 inch per second = 25.4 milimetre per second |
| 36 | 1 knot = 0.5144+ metre per second |
| 37 | 1 knot UK = 0.5147+ metre per second & 1.853 km per hour |
| 38 | 1 mile per hour = 0.4470+ metre per second & 1.609 km per hour |
| FUEL CONSUMPTION | |
| 39 | 1 gallon per mile = 2.825 litre per km |
| 40 | 1 US gallon per mile = 2.352 litre per km |
| 41 | 1 mile per gallon = 0.3540+ km per litre |
| 42 | 1 mile per US gallon = 0.4251+ km per litre |
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