Common non-SI units
The pursuit of standardized specification of physical quantities has led to the International System of Units (SI) . This is common all over the world, in most industrialized countries the use of SI units for official and business transactions is required by law.
For the European Union, Directive 80/181 / EEC of the European Council of December 20, 1979 stipulates the use of the International System of Units in business and official transactions. This was implemented into national law in Germany in the 1970s through the Units and Time Act , in Austria through the Measure and Verification Act , and in Switzerland there are corresponding regulations in the Federal Act on Metrology . In addition to the SI units, there are also other legal units . Since information in legal units is not required in many areas (e.g. in the field of research) or other units are permitted if they are given in addition to SI units, many such units are common in German-speaking countries. These common non-SI units are listed below.
Units approved for use with the SI
The International Bureau of Weights and Measures (BIPM) publishes in a brochure Le Système international d'unités - also known as "the SI brochure" in German and adapted by PTB for Germany - in addition to the SI units, also the units that Are "approved for use with the SI".
The following complete list of units that are “approved for use with the SI” is arranged according to the associated size. Some of these units can also be used together with SI prefixes (such as “kilo” or “milli”).
- Minute (min), hour (h) and day (d ; "standard day"):
- 1 min = 60 s
- 1 h = 60 min = 3600 s
- 1 d = 24 h = 1440 min = 86 400 s
The use of SI prefixes with these three time units is not permitted according to the SI brochure. The year is not listed as an accepted unit, but is generally used, also in legal texts, e.g. B. when specifying times for dates and deadlines .
- Astronomical Unit (abbreviated AE , international au for Astronomical Unit )
- 1 ha = 100 a = 10 4 m 2 = 10 000 m 2
- The (or the) hectare is a legal unit in Germany, Austria and Switzerland - there with the unit name “hectare” - but limited to the indication of the area of land and parcels. According to the EEC guideline 80/181 / EEC, “hectare” is just a special name for one hundred times Ar , formed from the prefix hecto for 100 and the unit name Ar.
Liter (l or L):
- 1 l = 1 L = 1 dm 3 = 1 000 cm 3 = 10 −3 m 3
- 1 t = 1 Mg = 10 3 kg = 1,000 kg
Atomic mass unit (u), also called dalton (Da)
- 1 u = 1.660 538 782 (83)e-27 kg
- The atomic mass unit is used to indicate atomic and molecular masses.
Electron volt (eV)
- 1 eV = 1.602 176 634e-19 y
- The electron volt (or "electron volt") is used to indicate energies in atomic, nuclear and particle physics.
Sizes of the dimension number
Degrees (°) with arc minutes (′) and arc seconds (″) for plane angles:
- 1 ° = (π / 180) rad
- 1 ′ = (1/60) ° = (π / 10 800) rad
- 1 ″ = (1/60) ′ = (π / 648 000) rad
- Bel (B) and Neper (Np) for logarithmic ratios , for example for the sound pressure level and the gain
Other statutory non-SI units in the EU or Switzerland
Statutory non-SI entities in the European Union
Further units outside the SI are "legal units" according to Directive 80/181 / EEC . This is implemented essentially identically in national laws in all EU countries. For Germany, the Physikalisch-Technische Bundesanstalt (PTB) lists such non-SI units in the constantly updated brochure “The legal units in Germany”.
- Ar (a):
- 1 b = 100 fm 2 = 10 −24 cm 2 = 10 −28 m 2
- The barn is used in nuclear physics as a unit for specifying effective cross sections.
Metric carat = 0.2 g
- Mass of precious stones, especially diamonds
- According to the EEC guideline, no unit symbol is specified for the metric carat.
- 1 bar = 100 kPa = 10 5 Pa
Millimeter Mercury Column - (mmHg):
- 1 mmHg = (101 325/760) Pa ≈ 133.322 Pa (only for blood pressure measurement ). The unit is the legal unit for specifying blood pressure and the pressure of other body fluids. In the EEC guideline, the unit symbol is written with a space: mm Hg, in the national laws of Germany, Austria and Switzerland as mmHg.
Kilowatt hour (kWh):
- 1 kWh = 3.6 megajoules (MJ)
- To determine the electricity and heating costs.
- Voltampere (VA) and Var (var):
Refractive power of optical systems
- 1 dpt = 1 m −1
- 1 tex = 1 g / km = 10 −6 kg m −1
- Length-related mass of textile fibers and yarns.
Exceptions in Ireland
For volume information when serving beer and cider on tap and for milk in reusable containers:
- Pint (pt):
- 1 pt = 568.3 cm 3
For mass information when trading in precious metals:
Troy ounce , troy ounce (oz tr):
- 1 oz tr = 31.1034768 g
Statutory non-SI units in Switzerland
- Are (a) and hectares (ha):
- 1 ha = 100 a = 10,000 m 2
- In Switzerland, the Ar has the unit name "Are" and is the legal unit for specifying the area of land and parcels.
- metric carat (ct):
- As a unit symbol, ct is the legal unit symbol in Switzerland.
- The use of the intent is not permitted.
- Decibel (dB):
- Sound pressure level = 20 dB · lg (sound pressure / 20 µPa)
- Sound power level = 10 dBlg (sound power / 1 pW)
- Sound intensity level = 10 dBlg (sound intensity / 1 pW / qm)
- Sound velocity level = 20 dBlg (sound velocity / 50 nm / s)
- The use of the intent is not permitted.
Other non-SI units
In colloquial but also in technical language usage, some units or unit symbols are used that are not or only partially compliant with the International System of Units. Some examples of such units or symbols are:
- Phon , Sone (sone) and Mel (mel)
- the inch (″), e.g. B. to specify the diagonal of screens or the diameter of car or bicycle rims and the Whitworth thread of pipes, as well as hard drives and storage media , often in connection with American products:
- 1 ″ = 25.4 mm
- One inch corresponds exactly to one inch (see above).
- 1 foot = 12 inches = 30.48 cm
- Foot is common in international aviation and shipping.
- Ångström (Å)
- 1 nautical mile = 1852 m
- Nautical mile (or nautical mile) is common in international aviation and shipping.
Astronomical units of length
- see above Units approved for use with the SI
Light year (Lj, ly) with light second, light minute, light hour and light day
- 1 ly = 9 460 730 472 580 800 m
- The light year is often used in publications addressed to the general public.
- 1 pc ≈ 30.856 776e15 m
- The parsec is the most frequently used astronomical unit of length in scientific practice. 1 pc is roughly 3.262 light years.
- Solid cubic meters (Fm) and cubic meters (Rm) instead of m 3 , for the volume of long timber and plywood (legal units until 1977)
- Barrels in the petroleum trade
Units in food chemistry
Must weight and sugar content
- Degree Oechsle (° Oe)
- Klosterneuburg sugar grades (° KMW)
Original wort content
Acidity of milk and dairy products
Degree Soxhlet handle (° SH)
- used in Central Europe
Diastatic power of beers
Degree Windisch-Kolbach (° WH)
- common in Europe
Degree of German hardness (° dH)
- used in Germany and Austria
Degree of French hardness (° fH)
- common in France and Switzerland
- Hecto instead of hectogram (especially in Italy and Sweden )
- Deka instead of Dekagramm (especially in Austria , Hungary and the Czech Republic )
- Re-use of the pound and the hundredweight (in the sense of 0.5 kg or 50 kg, the latter in Switzerland, Austria and Russia 100 kg)
Time and time-related quantities
- “Auxiliary word / time unit” instead of specifying frequencies in the unit 1 / s or s −1
- 1 knot (kn) = 1 knot = 1 nautical mile / h = 1.852 km / h ≈ 0.514444 m / s
- The knot is used as a unit of speed in international aviation and shipping.
- Radar kilometers (radar mile)
- 1 radar kilometer = 6.66 µs (1 radar mile = 12.35 µs)
- The radar kilometer describes the transit time which an electromagnetic wave needs for 1 kilometer ( i.e. for 1 km there and 1 km back), the radar mile 1.852 times the radar kilometer.
- In the nutrition sector, the physiological calorific value of food (in addition to the SI unit joule ) is still given in the unit kilocalorie (kcal) (base unit calorie (cal)).
- The use of horsepower ( horsepower ) instead of the legal unit kilowatt (kW) is colloquially widespread especially in motor vehicles.
- Further piece dimensions such as B. the dozen = 12 pieces
- ppb for “parts per billion” and ppt for “parts per trillion” or “parts per thousand”. Since the meaning of the number names billion and trillion is not the same in all languages, the use of these expressions or abbreviations is not recommended.
- See explanation on p. 6 of the SI brochure of the PTB
- Le Système international d'unités . 9e édition, 2019 (the so-called "SI brochure", French and English).
- The International System of Units (SI) . German translation of the BIPM brochure "Le Système international d'unités / The International System of Units (8e édition, 2006)". In: PTB-Mitteilungen . tape 117 , no. 2 , 2007 ( ptb.de [PDF; 1.4 MB ] Please note: This is the translation of the SI brochure from 2006. The list of “units outside the SI whose use in connection with the SI is permitted” does not correspond to the status since 2019. The translation of the current version is not yet available in front.).
- Appendix 1 of the "Implementing Ordinance to the Law on Units in Metrology and Time Determination (Units Ordinance - EinhV)"
- Art. 18 of the Swiss Unit Ordinance
- (PDF) (as of 2012)
- The legal units in Germany, as of June 2015 ( Memento from September 24, 2015 in the Internet Archive )
- Foreign exchange rates, euro reference rates, gold, check collection rates. Deutsche Bundesbank, accessed on February 2, 2014 .
- Definition in the radar tutorial