- 1). Start at 275 degrees Fahrenheit for gas mark one. Subtract one from the gas mark, only for gas marks two and above, and multiply by 25. For gas mark 1/2, use 250 degrees Fahrenheit and use 225 degrees Fahrenheit for gas mark 1/4.
- 2). Add this number to 275 to determine the temperature in degrees Fahrenheit. For instance, a recipe using gas mark 5, subtract 1 from 5 to get 4. Multiply 4 by 25 degrees Fahrenheit equals 100 degrees Fahrenheit. Add this to 275 to determine the final oven temperature in degrees Fahrenheit of 375 degrees Fahrenheit.
- 3). Convert the degrees Fahrenheit to Celsius by subtracting 32 from the temperature. In the example: 375 minus 32 equals 343. Multiply this number by (5/9) to find the temperature in degrees Celsius. For example, 343 multiplied by 5/9 equals 190.556 degrees Celsius. Round this to 190 degrees Celsius.
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