Old recipes require some adjustments of their numbers before baking them in a Older model European stoves often used gas marks for their oven thermostat dials, but to prepare a recipe requiring your food to cook at a specific temperature in your new oven, you must convert the gas mark to degrees Fahrenheit and then to Celsius. Learning to convert from a gas mark to Fahrenheit to Celsius might seem like an additional step, but you will be better prepared to use the formula for converting oven temperatures in any recipe whether it requires gas marks, degrees Fahrenheit or degrees Celsius. Never let the temperature unit in a recipe prevent you from making it again since you now know its equivalent.
Start at 135 degrees Celsius 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 121 degrees Celsius and use 107 degrees Celsius for gas mark 1/4.
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 0-3.889 degrees Celsius equals 37.8 degrees Celsius. Add this to 275 to determine the final oven temperature in degrees Fahrenheit of 191 degrees Celsius.
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.