This MedLibrary.org supplementary page on Non-SI units accepted for use with SI is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
The following units are not SI units but are "accepted for use with the International System."
| Name | Symbol | Quantity | Equivalent SI unit |
|---|---|---|---|
| minute | min | time (multiple unit) | 1 min = 60 s |
| hour | h | time (multiple unit) | 1 h = 60 min = 3600 s |
| day | d | time (multiple unit) | 1 d = 24 h = 1440 min = 86400 s |
| degree of arc | ° | angle (non unitary unit) | 1° = (π/180) rad |
| minute of arc | ′ | angle (non unitary unit) | 1′ = (1/60)° = (π/10800) rad |
| second of arc | ″ | angle (non unitary unit) | 1″ = (1/60)′ = (1/3600)° = (π/648000) rad |
| square degree | deg² or sq.deg. | solid angle | 1 deg² = (π/180) sr. |
| hectare | ha | area (simple decimal multiple unit) | 1 ha = 100 a = 10000 m² |
| litre | l or L | volume (simple decimal multiple unit) | 1 dm3 = 0.001 m3 |
| tonne | t | mass (simple decimal multiple unit) | 1 t = 103 kg = 1 Mg |
The square degree unit is mostly used in astronomy and optic (its usage is strongly discouraged in all other domains, including in cartography). The whole sphere covers a solid angle (seen from its centre) of (129600/π) deg² (approx. 41252.961 deg²) and is the solid angle covered by a conic section of a sphere, whose opening apex is exactly 360° (note that the measure of a solid angle in square degrees is not proportional (and does not vary polynomially with) the measure of the associated planar angle in degrees of opening of its associated cone. In cartography, you can't simply multiply a difference of longitudes and a difference of latitudes, both expressed in degrees to get an exact measure of a solid angle in square degrees (this will just be an approximation only if these differences are very small, below one minute of arc each, and the covered area is very near the equator, i.e. at very low latitudes where the small area will be nearly rectangular instead of being nearly trapezoidal in median latitudes, or nearly a disc sector near the poles).
| Name | Symbol | Quantity | Equivalent SI unit |
|---|---|---|---|
| neper, field quantity | Np | ratio (dimensionless) | LF = ln(F/F0) Np |
| neper, power quantity | Np | ratio (dimensionless) | LP = ½ ln(P/P0) Np |
| bel, field quantity | B | ratio (dimensionless) | LF = 2 log10(F/F0) B |
| bel, power quantity | B | ratio (dimensionless) | LP = log10(P/P0) B |
| Name | Symbol | Quantity | Equivalent SI unit |
|---|---|---|---|
| electronvolt | eV | energy | 1 eV = 1.60217733 (49) × 10−19 J |
| atomic mass unit | u | mass | 1 u = 1.6605402 (10) × 10−27 kg |
| astronomical unit | AU | length | 1 AU = 1.49597870691 (30) × 1011 m |
| Name | Symbol | Quantity | Equivalent SI unit |
|---|---|---|---|
| Ångström, angstrom | Å | length | 1 Å = 0.1 nm = 10−10 m |
| nautical mile | length | 1 nautical mile = 1852 m | |
| knot | speed | 1 knot = 1 nautical mile per hour = (1852/3600) m/s | |
| are | a | area | 1 a = 1 dam2 = 100 m2 |
| barn | b | area | 1 b = 10−28 m² |
| bar | bar | pressure | 1 bar = 105 Pa |
| millibar | mbar | pressure | 1 mbar = 1 hPa = 100 Pa (was used in atmospheric meteorology, the preferred unit is now the hectopascal) |
| atmosphere | atm | pressure | 1 atm = 1013.25 mbar = 1013.25 hPa] = 1.01325×105 Pa (commonly used in atmospheric meteorology, in oceanology and for pressures within liquids, or in the industry for pressures within containers of liquified gas) |
References
- Taylor, Barry N. (ed.) (2001). The International System of Units (SI) (2001 ed., Special Publication 330). Gaithersburg, Maryland: National Institute of Standards and Technology. pp. 15–19. Viewed at http://physics.nist.gov/Pubs/SP330/sp330.pdf
- "Non-SI units accepted for use with the SI, and units based on fundamental constants". SI brochure (8th edition). BIPM. Retrieved on 2008-03-08.
Wikipedia content modification information:
- This page was last modified on 29 August 2008, at 11:51.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Non-SI units accepted for use with SI".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.