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SI Units and Measurements
A compact, tabular revision of SI base and derived units, the quantities they measure, common non-SI units, prefixes and physical constants, for CAPF Paper I General Science
CAPF wiki•4 min read•8 sections
At a glance
SubjectGeneral Science
RevisionGeneral ScienceSi UnitsMeasurementsPhysicsPaper 1
One screen per section. Cover the right column and test yourself. The SI (Systeme International d'Unites) is the modern metric system with seven base units; everything else is derived from them. CAPF Paper I tests the "quantity to unit" pairing and a few standard non-SI units. Numerical values of constants below are the standard textbook figures; for the formally redefined values verify the latest.
| Quantity |
SI base unit |
Symbol |
| Length |
metre |
m |
| Mass |
kilogram |
kg |
| Time |
second |
s |
| Electric current |
ampere |
A |
| Temperature |
kelvin |
K |
| Amount of substance |
mole |
mol |
| Luminous intensity |
candela |
cd |
Note: mass, not weight, is a base quantity. Weight is a force (newton). The kilogram is the only base unit that historically carried the "kilo" prefix in its name.
| Quantity |
Derived unit |
In base terms |
| Force |
newton (N) |
kg m/s squared |
| Energy / work |
joule (J) |
N m |
| Power |
watt (W) |
J/s |
| Pressure |
pascal (Pa) |
N/m squared |
| Frequency |
hertz (Hz) |
per second |
| Electric charge |
coulomb (C) |
A s |
| Potential difference |
volt (V) |
J/C |
| Electrical resistance |
ohm |
V/A |
| Capacitance |
farad (F) |
C/V |
| Magnetic flux |
weber (Wb) |
V s |
| Magnetic flux density |
tesla (T) |
Wb/m squared |
| Illuminance |
lux (lx) |
lumen/m squared |
| Quantity |
Unit |
| Area |
square metre |
| Volume |
cubic metre (litre as non-SI) |
| Density |
kilogram per cubic metre |
| Velocity / speed |
metre per second |
| Acceleration |
metre per second squared |
| Momentum |
kilogram metre per second |
| Heat |
joule (calorie as non-SI) |
| Sound intensity (level) |
decibel (dB) |
| Radioactivity |
becquerel (Bq); older unit curie |
| Absorbed radiation dose |
gray (Gy); older unit rad |
| Equivalent dose |
sievert (Sv) |
| Unit |
Measures / equals |
| Light year |
Distance light travels in one year (about 9.46 trillion km), a unit of distance not time |
| Astronomical unit (AU) |
Mean Earth to Sun distance (about 149.6 million km) |
| Parsec |
About 3.26 light years |
| Angstrom |
One ten-billionth of a metre (10 to the power minus 10 m); atomic and wavelength scale |
| Nautical mile |
About 1.852 km; used at sea and in aviation |
| Knot |
One nautical mile per hour (speed) |
| Horsepower |
About 746 watts |
| Carat |
Mass of gemstones (200 mg); also gold purity (karat) |
| Bar |
Pressure; 1 bar is about 100,000 pascal |
| Calorie |
Heat; about 4.18 joules |
| Hertz |
Cycles per second (frequency) |
| Prefix |
Symbol |
Factor |
| giga |
G |
10 to the power 9 |
| mega |
M |
10 to the power 6 |
| kilo |
k |
10 to the power 3 |
| centi |
c |
10 to the power minus 2 |
| milli |
m |
10 to the power minus 3 |
| micro |
(mu) |
10 to the power minus 6 |
| nano |
n |
10 to the power minus 9 |
| pico |
p |
10 to the power minus 12 |
| Constant |
Standard value |
| Speed of light in vacuum |
about 3 times 10 to the power 8 m/s |
| Acceleration due to gravity (Earth, mean) |
about 9.8 m/s squared |
| Standard atmospheric pressure |
about 101,325 pascal (760 mm of mercury) |
| Speed of sound in air (room temperature) |
about 343 m/s |
| Absolute zero |
0 kelvin, equal to about minus 273.15° Celsius |
| Avogadro number |
about 6.022 times 10 to the power 23 per mole |
| Conversion |
Relation |
| Celsius to Fahrenheit |
F equals (9/5)C plus 32 |
| Celsius to Kelvin |
K equals C plus 273.15 |
| Freezing point of water |
0 C, 32 F, 273.15 K |
| Boiling point of water (sea level) |
100 C, 212 F, 373.15 K |