Conversion Between SI and Legacy Units
During its evolution, the metric system has adopted many units of measure. The introduction of SI rationalised both the way in which units of measure were defined and also the list of units in use. These are now catalogued in the official SI Brochure. The table below lists the units of measure in this catalogue and shows the conversion factors connecting them with the equivalent units that were in use on the eve of the adoption of SI.
| Quantity | Dimension | SI unit and symbol | Legacy unit and symbol | Conversion factor |
|---|---|---|---|---|
| Time | second (s) | second (s) | 1 | |
| Length | metre (m) | centimetre (cm) ångström (Å) |
0.01 10−10 |
|
| Mass | kilogram (kg) | gram (g) | 0.001 | |
| Electric current | ampere (A) | international ampere abampere or biot statampere |
1.000022 10.0 3.335641×10−10 |
|
| Temperature | kelvin (K) degrees Celsius (°C) |
centigrade (°C) | = + 273.15 1 |
|
| Luminous intensity | candela (cd) | international candle | 0.982 | |
| Amount of substance | mole (mol) | No legacy unit | n/a | |
| Area | square metre (m2) | are (are) | 100 | |
| Acceleration | (ms−2) | gal (gal) | 10−2 | |
| Frequency | hertz (Hz) | cycles per second | 1 | |
| Energy | joule (J) | erg (erg) | 10−7 | |
| Power | watt (W) | (erg/s) horsepower (HP) Pferdestärke (PS) |
10−7 745.7 735.5 |
|
| Force | newton (N) | dyne (dyn) sthene (sn) kilopond (kp) |
10−5 103 9.80665 |
|
| Pressure | pascal (Pa) | barye (Ba) pieze (pz) atmosphere (at) |
0.1 103 1.01325×105 |
|
| Electric charge | coulomb (C) | abcoulomb statcoulomb or franklin |
10 3.335641×10−10 |
|
| Potential difference | volt (V) | international volt abvolt statvolt |
1.00034 10−8 2.997925×102 |
|
| Capacitance | farad (F) | abfarad statfarad |
109 1.112650×10−12 |
|
| Inductance | henry (H) | abhenry stathenry |
10−9 8.987552×1011 |
|
| Electric resistance | ohm (Ω) | international ohm abohm statohm |
1.00049 10−9 8.987552×1011 |
|
| Electric conductance | siemens (S) | international mho (℧) abmho statmho |
0.99951 109 1.112650×10−12 |
|
| Magnetic flux | weber (Wb) | maxwell (Mx) | 10−8 | |
| Magnetic flux density | tesla (T) | gauss (G) | 1×10−4 | |
| Magnetic field strength | (A/m) | oersted (Oe) | 103/4π = 79.57747 | |
| Dynamic viscosity | (Pa·s) | poise (P) | 0.1 | |
| Kinematic viscosity | (m2s−1) | stokes (St) | 10−4 | |
| Luminous flux | lumen (lm) | stilb (sb) | 104 | |
| Illuminance | lux (lx) | phot (ph) | 104 | |
| activity | becquerel (Bq) | curie (Ci) | 3.70×1010 | |
| Absorbed dose | gray (Gy) | roentgen (R) rad (rad) |
2.58×10−4 0.01 |
|
| Radiation dose equivalent | sievert | roentgen equivalent man (rem) | 0.01 | |
| Catalytic activity | katal (kat) | No legacy unit | n/a |
The SI Brochure also catalogues certain non-SI units that are widely used with the SI in matters of everyday life or units that are exactly defined values in terms of SI units and are used in particular circumstances to satisfy the needs of commercial, legal, or specialised scientific interests. These units include:
| Quantity | Dimension | Unit and symbol | Equivalence |
|---|---|---|---|
| Mass | tonne (t) | 1000 kg | |
| Area | hectare (ha) | 0.01 km2 104 m2 |
|
| Volume | litre (L or l) | 0.001 m3 | |
| Time | minute (min) hour (h) day (d) |
60 s 3600 s 86400 s |
|
| Pressure | bar | 100 kPa | |
| Plane angle | degree (°) minute (ʹ) second (″) |
(π⁄180) rad (π⁄10800) rad (π⁄648000) rad |
Read more about this topic: Metric System
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