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Gas Mark to Fahrenheit Converter

Enter a gas mark or temperature to convert oven heat settings.

How it is calculated

The engine treats gas marks as a straight line: °F = 250 + 25 × GM, where GM is the gas mark number. Celsius is then °C = (°F − 32) × 5 ÷ 9. In the reverse direction it solves the same line: GM = (°F − 250) ÷ 25. Results are rounded to a whole degree (gas mark to one decimal place). The line holds for whole marks from 1 upwards; the tool only accepts gas marks from 1 to 30 and, in reverse, temperatures from 250 °F to 1000 °F, and returns nothing outside those ranges. The fractional low marks (¼, ½) used on some British ovens are not part of this formula, so look those up in your oven manual.

Worked example

Say a recipe calls for gas mark 6. Multiply by 25: 6 × 25 = 150. Add 250: 250 + 150 = 400, so the oven setting is 400 °F. For Celsius subtract 32 (368), multiply by 5 (1840) and divide by 9, which gives 204.4, shown as 204 °C. Going back, 400 °F gives (400 − 250) ÷ 25 = 6.0 gas mark.

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Common mistakes

  • Entering an oven temperature while the direction is set to gas mark to °F. A value like 180 is read as gas mark 180 and rejected, because gas marks stop at 30.
  • Typing a Celsius temperature in the Fahrenheit reverse mode. 180 °C is about 356 °F, so convert it first or the tool will say 180 is out of range.
  • Expecting a result for gas mark ¼ or ½. The straight-line formula does not cover them, and the tool returns nothing below gas mark 1.
  • Treating the rounded Celsius value as exact. 204 °C is rounded from 204.4, and fan ovens usually need a lower setting than the recipe states.

About this calculator

The gas mark scale is a British system for oven temperatures, historically tied to the pressure setting on gas ovens, running from a low gas mark 1 (about 275°F/135°C) up through gas mark 9 (about 475°F/246°C) in fixed 25°F steps. This converter translates a gas mark from 1 upward into its Fahrenheit equivalent, along with the matching Celsius reading, and can also turn a Fahrenheit temperature between 250°F and 1000°F back into a gas mark, since gas mark, Fahrenheit, and Celsius are the three temperature systems that appear interchangeably across older and modern British recipes.

It's a practical kitchen reference for home cooks following British or Commonwealth recipes on an oven dialed in Fahrenheit or Celsius, since many classic UK cookbooks — and plenty of newer ones — still list oven heat purely as a gas mark number without a numeric temperature alongside it.

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Comments (1)

  • Editorial team

    Oven recipes usually round, and so does the tool: gas mark 4 gives 350 °F and 177 °C, although most recipes say 180 °C. Mark 6 gives 400 °F and 204 °C, and mark 9 gives 475 °F. Going backwards, 375 °F returns gas mark 5.0, but a value like 180 returns nothing because the reverse direction expects Fahrenheit. Fractional marks are not covered. Which recipes are you trying to convert?

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