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Examples

• Typical bacteria are 1 to 10 μm in diameter.
• Human hair typically varies in diameter from 17 to 181 μm.⁴
• Eukaryotic cells are typically 10 to 100 μm in diameter.⁵

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Symbol encoding in character sets

The official symbol for the SI prefix micro is a Greek lowercase mu (μ).¹⁰ For reasons stemming from its design, Unicode has two different character codes for the letter, with slightly different appearance in some fonts, although most fonts use the same glyph. U+00B5 µ MICRO SIGN (Alt+0181) is in the "Latin-1 Supplement" range identical to ISO/IEC 8859-1 (since 1987),¹¹ residing at this code point also in DEC MCS (since 1983) and ECMA-94 (since 1985). U+03BC μ GREEK SMALL LETTER MU (Alt+956) is in the Greek range. According to The Unicode Consortium, the Greek letter character is preferred,¹² but implementations must recognize the micro sign as well, for compatibility with legacy character sets. This distinction also occurs in some legacy code pages, notably Windows-1253.

In circumstances in which only the Latin alphabet is available, ISO 2955 (since 1974,¹³ withdrawn 2001¹⁴), DIN 66030 (since 1980¹⁵¹⁶) and BS 6430 (since 1983) allow the prefix μ to be substituted by the letter u (or even U, if lowercase letters are not available), as, for example, in um for μm, or uF for μF, or in the common abbreviation UC for microcontroller (μC). Similarly, capacitor values according to the RKM code defined in IEC 60062 (since 1952) can be written as 4u7 (or 4U7) instead of 4μ7 if the Greek letter μ is not available.

The CJK Compatibility block contains square forms of some Japanese katakana measure and currency units. U+3343 ㍃ SQUARE MAIKURO corresponds to マイクロ maikuro.

Other abbreviating conventions

In some health care institutions, house rules deprecate the standard symbol for microgram, "μg", in prescribing or chart recording, because of the risk of giving an incorrect dose because of the misreading of poor handwriting.¹⁷ The two alternatives are to abbreviate as "mcg"¹⁸¹⁹ or to write out "microgram" in full (see also List of abbreviations used in medical prescriptions). The alternative abbreviation may be ambiguous in rare circumstances in that mcg could also be read as a micrigram, i.e. 10−14 g; however the prefix micri is not standard, nor widely known, and is considered obsolete. This deprecation, focused on avoiding incorrect dosing in contexts where handwriting is often present, does not extend to all health-care contexts and institutions (for example, some clinical laboratories' reports adhere to it, whereas others do not²⁰), and in physical sciences research, "μg" remains the sole official abbreviation.

In medical data exchange according to the Health Level 7 (HL7) standard, the μ can be replaced by u as well.²¹

See also

• Microgram
• Microscope
• Microsecond
• Microwave
• Square micrometre
• List of commonly used taxonomic affixes

References

1. International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6, archived (PDF) from the original on 2021-06-04, retrieved 2021-12-16 92-822-2213-6 ↩

2. "MICR," Merriam-Webster.com Dictionary, https://www.merriam-webster.com/dictionary/MICR. Accessed 10/13/2024. https://www.merriam-webster.com/dictionary/MICR ↩

3. "ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations: Abbreviations for Doses/Measurement Units". Recommendations. Institute for Safe Medication Practices (ISMP). 2021-02-05. Archived from the original on 2022-12-24. Retrieved 2022-12-24. Error-Prone Abbreviations, Symbols, and Dose Designations: μg […] Intended Meaning: Microgram […] Misinterpretation: Mistaken as mg […] Best Practice: Use mcg […] https://www.ismp.org/recommendations/error-prone-abbreviations-list ↩

4. Ley, Brian (1999). Elert, Glenn (ed.). "Diameter of a human hair". The Physics Factbook. Retrieved 2018-12-08. https://hypertextbook.com/facts/1999/BrianLey.shtml ↩

5. Biology by Campbell & Reece, tenth edition. Ch. 6 "A Tour of the Cell". p. 98. ↩

6. Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873. /wiki/Centimetre%E2%80%93gram%E2%80%93second_system_of_units ↩

7. "On the extension of the range of SI prefixes". 2022-11-18. Retrieved 2023-02-05. https://www.bipm.org/en/cgpm-2022/resolution-3 ↩

8. "Metric (SI) Prefixes". NIST. https://www.nist.gov/pml/owm/metric-si-prefixes ↩

9. "On the extension of the range of SI prefixes". 2022-11-18. Retrieved 2023-02-05. https://www.bipm.org/en/cgpm-2022/resolution-3 ↩

10. Prefixes of the International System of Units, International Bureau of Weights and Measures (page visited on 9 May 2016). https://www.bipm.org/en/measurement-units/si-prefixes ↩

11. (Unicode 1.0, 1991) ↩

12. Unicode Technical Report #25 https://www.unicode.org/reports/tr25 ↩

13. ISO 2955-1974: Information processing - Representations of SI and other units for use in systems with limited character sets (1st ed.). 1974. ↩

14. "Table 2". ISO 2955-1983: lnformation processing - Representations of SI and other units for use in systems with limited character sets (PDF) (2nd ed.). 1983-05-15. Retrieved 2016-12-14. [1] http://isotc.iso.org/livelink/livelink/4289384/ISO_2955-1983E_repr_of_SI_units_with_limited_char_sets.pdf?func=doc.Fetch&nodeid=4289384 ↩

15. DIN 66030: Darstellungen von Einheitennamen in Systemen mit beschränktem Schriftzeichenvorrat (in German) (1st ed.). 1980. ↩

16. "Neue Normen für die Informationsverarbeitung". Computerwoche (in German). 1981-01-09. Archived from the original on 2016-12-14. Retrieved 2016-12-14. http://www.computerwoche.de/a/neue-normen-fuer-die-informationsverarbeitung,1184901 ↩

17. Burtis, Carl A.; Ashwood, Edward R.; Bruns, David E. (2012), Tietz Textbook of Clinical Chemistry and Molecular Diagnostics (5th ed.), Elsevier Health Sciences, ISBN 978-1455759422. 978-1455759422 ↩

18. Burtis, Carl A.; Ashwood, Edward R.; Bruns, David E. (2012), Tietz Textbook of Clinical Chemistry and Molecular Diagnostics (5th ed.), Elsevier Health Sciences, ISBN 978-1455759422. 978-1455759422 ↩

19. "ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations: Abbreviations for Doses/Measurement Units". Recommendations. Institute for Safe Medication Practices (ISMP). 2021-02-05. Archived from the original on 2022-12-24. Retrieved 2022-12-24. Error-Prone Abbreviations, Symbols, and Dose Designations: μg […] Intended Meaning: Microgram […] Misinterpretation: Mistaken as mg […] Best Practice: Use mcg […] https://www.ismp.org/recommendations/error-prone-abbreviations-list ↩

20. Burtis, Carl A.; Ashwood, Edward R.; Bruns, David E. (2012), Tietz Textbook of Clinical Chemistry and Molecular Diagnostics (5th ed.), Elsevier Health Sciences, ISBN 978-1455759422. 978-1455759422 ↩

21. "Commonly Used UCUM Codes for Healthcare Units". HL7 Deutschland e.V. 2015-11-21. Archived from the original on 2022-10-06. Retrieved 2022-12-24. https://download.hl7.de/documents/ucum/ucumdata.html ↩