The katal (symbol: kat) is the unit of catalytic activity in the International System of Units (SI)[1] used for quantifying the catalytic activity of enzymes (that is, measuring the enzymatic activity level in enzyme catalysis) and other catalysts.

Unit systemSI
Unit ofcatalysis
In SI base units:mol/s

The katal is invariant of the measurement procedure, but the measured numerical value is not; the value depends on the experimental conditions. Therefore, to define the quantity of a catalyst in katals, the rate of conversion of a defined chemical reaction is specified as moles reacted per second.[2] One katal of trypsin, for example, is that amount of trypsin which breaks one mole of peptide bonds in one second under specified conditions.


One katal refers to an enzyme catalysing the reaction of one mole of substrate per second.[3][4] Because this is such a large unit for most enzymatic reactions, the nanokatal (nkat) is used in practice.[4]

The katal is not used to express the rate of a reaction; that is expressed in units of concentration per second, as moles per liter per second. Rather, the katal is used to express catalytic activity, which is a property of the catalyst.

SI multiples

SI multiples of katal (kat)
Submultiples Multiples
Value SI symbol Name Value SI symbol Name
10−1 kat dkat decikatal 101 kat dakat decakatal
10−2 kat ckat centikatal 102 kat hkat hectokatal
10−3 kat mkat millikatal 103 kat kkat kilokatal
10−6 kat µkat microkatal 106 kat Mkat megakatal
10−9 kat nkat nanokatal 109 kat Gkat gigakatal
10−12 kat pkat picokatal 1012 kat Tkat terakatal
10−15 kat fkat femtokatal 1015 kat Pkat petakatal
10−18 kat akat attokatal 1018 kat Ekat exakatal
10−21 kat zkat zeptokatal 1021 kat Zkat zettakatal
10−24 kat ykat yoctokatal 1024 kat Ykat yottakatal
10−27 kat rkat rontokatal 1027 kat Rkat ronnakatal
10−30 kat qkat quectokatal 1030 kat Qkat quettakatal


The General Conference on Weights and Measures and other international organizations recommend use of the katal.[5] It replaces the non-SI enzyme unit of catalytic activity. The enzyme unit is still more commonly used than the katal,[4] especially in biochemistry. The adoption of the katal has been slow.[4][6]


The name "katal" has been used for decades. The first proposal to make it an SI unit came in 1978,[4][7] and it became an official SI unit in 1999.[4][8][9] The name comes from the Ancient Greek κατάλυσις (katalysis), meaning "dissolution";[10] the word "catalysis" itself is a Latinized form of the Greek word.[10][11]


  1. Nomenclature Committee of the International Union of Biochemistry (NC-IUB) (1979). "Units of Enzyme Activity". European Journal of Biochemistry. 97 (2): 319–20. doi:10.1111/j.1432-1033.1979.tb13116.x. Archived from the original on 4 May 2022.
  2. Dybkær, René (2001). "UNIT "KATAL" FOR CATALYTIC ACTIVITY (IUPAC Technical Report)" (PDF). Pure and Applied Chemistry. 73 (6): 927–931. doi:10.1351/pac200173060927. S2CID 195819612.
  3. Tipton, Keith F.; Armstrong, Richard N.; Bakker, Barbara M.; Bairoch, Amos; Cornish-Bowden, Athel; Halling, Peter J.; Hofmeyr, Jan-Hendrik; Leyh, Thomas S.; Kettner, Carsten; Raushel, Frank M.; Rohwer, Johann; Schomburg, Dietmar; Steinbeck, Christoph (2014-05-01). "Standards for Reporting Enzyme Data: The STRENDA Consortium: What it aims to do and why it should be helpful". Perspectives in Science. 1 (1–6): 131–137. doi:10.1016/j.pisc.2014.02.012. ISSN 2213-0209.
  4. Baltierra-Trejo, Eduardo; Márquez-Benavides, Liliana; Sánchez-Yáñez, Juan Manuel (2015-12-01). "Inconsistencies and ambiguities in calculating enzyme activity: The case of laccase". Journal of Microbiological Methods. 119: 126–131. doi:10.1016/j.mimet.2015.10.007. ISSN 0167-7012. PMID 26459230.
  5. "SI Brochure, Table 3: Coherent derived units in the SI with special names and symbols)". Bureau international des poids et mesures (BIPM). Retrieved 2019-05-13.
  6. Dybkaer, René (March 2002). "The tortuous road to the adoption of katal for the expression of catalytic activity by the General Conference on Weights and Measures". Clinical Chemistry. 48 (3): 586–590. doi:10.1093/clinchem/48.3.586. ISSN 0009-9147. PMID 11861460.
  7. "Units of Enzyme Activity Recommendations 1978". European Journal of Biochemistry. Nomenclature Committee of the International Union of Biochemistry (NC-IUB). 97 (2): 319–320. 1979. doi:10.1111/j.1432-1033.1979.tb13116.x.
  8. Dybkær, René (2001). "UNIT "KATAL" FOR CATALYTIC ACTIVITY (IUPAC Technical Report)" (PDF). Pure and Applied Chemistry. 73 (6): 927–931. doi:10.1351/pac200173060927. S2CID 195819612.
  9. "Topic 20: Working with enzymes" (PDF). The Association for Science Education. 2016. Retrieved 31 October 2020.
  10. Houghton Mifflin Harcourt, The American Heritage Dictionary of the English Language, Houghton Mifflin Harcourt
  11. Harper, Douglas. "catalysis (n.)". Etymonline. Retrieved 2019-04-03.
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