The draft 2003 edition of the Oxford English Dictionary lists the earliest known usage of the concept as being in L. Chatterton's book Modern Cookery published in 1943: "Afternoon tea scones… Time: 20 minutes. Temperature: Gas, Regulo Mark 7". "Regulo" was a type of gas regulator used by a manufacturer of cookers; however, the scale has now become universal, and the word Regulo is rarely used.
The term "gas mark" was a subject of the joint BBC/OED production Balderdash & Piffle, in May 2005. The earliest printed evidence of use of "gas mark" (with no other terms between the two words) appears to date from 1958. However, the manufacturers of the "New World" gas ranges in the mid-1930s gave away recipe books for use with their cooker, and the "Regulo" was the gas regulator. The book has no reference to degrees, either in Fahrenheit or (as then) Centigrade. All dishes to be cooked are noted to be at "Regulo Mark X".
Equivalents in Fahrenheit and Celsius
Gas mark 1 is 275 °Fahrenheit (135 °Celsius). Oven temperatures increase by 25 °F (13.9 °C) each time the gas mark increases by 1. Below Gas Mark 1 the scale markings halve at each step, each representing a decrease of 25 °F.
To convert gas mark to degrees Celsius (D), multiply the gas mark number (G) by 14, then add 121
(G × 14) + 121 = D
For the reverse conversion, G = (D - 121)/14
(These do not work for G less than 1.)
However it is usual to round the result of this calculation to a round number of degrees Celsius.
(Appropriate references can found in the section above.)
|1⁄4||225°||107°||Very Slow/Very Low|
|1⁄2||250°||121°||Very Slow/Very Low|
Other cooking temperature scales
French ovens and recipes often use a scale curiously based on the Fahrenheit scale, which itself has never been used in France: "Thermostat" (abbreviated "Th"), where Thermostat 1 equals 100 °F for conventional ovens, increasing by 50 °F for each whole number along the scale.
In Germany, "Stufe" (the German word for "step") is used for gas cooking temperatures. Gas ovens are commonly marked in steps from 1 to 8, corresponding to:
|Approx. Temp.||150 °C||175 °C||200 °C||225 °C||250 °C||275 °C||300 °C||325 °C|
Other ovens may be marked on a scale of 1-7, where Stufe ½ is about 125 °C in a conventional oven, Stufe 1 is about 150 °C, increasing by 25 °C for each subsequent step, up to Stufe 7 at 300 °C.
-  Archived June 25, 2007, at the Wayback Machine.
- "Gourmet Britain / Food Encyclopedia / Regulo TM settings". Gourmetbritain.com. Retrieved 29 October 2014.
- "Conversion Guides". BBC Good Food. Retrieved 14 March 2015.
- "Cooking Conversion Charts". The Guardian. Retrieved 14 March 2015.
- "Oven Temperatures". Practically Edible. 5 October 2007. Archived from the original on 30 June 2010. Retrieved 20 June 2010.
- "Temperatur-Angaben". GuteKueche. Retrieved 11 Feb 2012.