Gas mark

A Parkinson Cowan Prince gas cooker dial with a gas mark scale

The gas mark is a temperature scale used on gas ovens and cookers in the United Kingdom, Ireland and some Commonwealth of Nations countries.

History

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 and 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. All dishes to be cooked are noted to be at "Regulo Mark X".

Equivalents in Fahrenheit and Celsius

Gas mark 1 is 275 degrees Fahrenheit (135 degrees Celsius).

Oven temperatures increase by 25 °F (14 °C) for each gas mark step. Above Gas Mark 1, the scale markings increase by one for each step. Below Gas Mark 1, the scale markings halve at each step, each representing a decrease of 25 °F (14 °C).

Formulae

In theory, the following formulae can be used to convert between gas mark values and Celsius.

For temperatures above 135 °C (gas mark 1), to convert gas mark to degrees Celsius (${\textstyle C}$), multiply the gas mark number (${\textstyle G}$) by 14, then add 121:

$\left(G\times 14\right)+121=C$

For the reverse conversion:

$G={\frac {\left(C-121\right)}{14}}$

These do not work for ${\textstyle G}$ less than 1, since the steps are given as halves (i.e., 1⁄4, 1⁄2). For temperatures below 135 °C (gas mark 1), to convert gas mark to degrees Celsius apply the following conversion:

$C={\frac {243-(25\times \log _{2}(G^{-1}))}{1.8}}$

For the reverse:

$G=2^{(1.8C-243)/25}$

Note that tables of temperature equivalents for kitchen use conventionally round Celsius values to the nearest 10 degrees, with steps of either 10 or 20 degrees between Gas Marks.

Conversion table

In practice, of course, a conversion table is used instead of the above formulae. The numbers in the conversion table below represent values that would actually be given in a recipe or set on a stove.

Conversion table

Gas Mark	Fahrenheit	Celsius	Description
1⁄4	225	110	Very slow/Very low/Very cool
1⁄2	250	120	Very slow/Very low/Very cool
1	275	140	Slow/Low/Cool
2	300	150	Slow/Low/Cool
3	325	170	Moderately slow/Warm/Moderate
4	350	180	Moderate/Medium
5	375	190	Moderate/Moderately hot
6	400	200	Moderately hot
7	425	220	Hot
8	450	230	Hot/Very hot
9	475	240	Very hot
10 (less common)	500	260	Extremely hot

Other cooking temperature scales

French ovens and recipes use a scale based on the Celsius scale:"Thermostat" (abbreviated "Th"), where Thermostat 1 equals 30 °C for conventional ovens, increasing by 30 °C 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:

Stufe	1	2	3	4	5	6	7	8
Approx. Temp.	140 °C	160 °C	180 °C	200 °C	220 °C	240 °C	260 °C	280 °C

Other ovens may be marked on a scale of 1–7, where Stufe 1⁄2 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.

See also

• Outline of metrology and measurement