Why oven temperatures are written in three completely different systems
Celsius is the standard across most of the world, Fahrenheit remains standard in the United States, and Gas Mark is still commonly printed on UK recipes and older gas oven dials, especially in Britain, Ireland and parts of the Commonwealth. A recipe from any of these regions will assume you know its temperature system, which is exactly the problem this converter solves — enter a value in whichever unit your recipe uses and see it in all three instantly.
Gas Mark is the odd one out because it isn't a linear temperature scale at all — it's a numbered dial setting that roughly corresponds to specific Celsius and Fahrenheit values, which is why this tool uses a lookup table rather than a formula for that conversion.
The difference between a conventional oven and a fan oven
Fan (also called convection) ovens circulate hot air with a built-in fan, which cooks food faster and more evenly than a conventional oven at the same dial temperature. As a widely used rule of thumb, a fan oven should be set about 20°C (or roughly 20°F on that scale) lower than the temperature stated for a conventional oven to achieve a similar result, which is why this tool includes a fan-adjusted suggestion alongside the standard conversion.
If your recipe was written specifically for a fan oven already, you do not need to apply this adjustment again — check your recipe's wording, since some already specify 'fan' or 'convection' temperatures.
Practical tips when converting oven temperatures
Oven thermostats, especially in older ovens, are frequently inaccurate by 10-15°C in either direction, so a converted temperature is a starting point, not a guarantee — an oven thermometer placed inside the oven is the only way to know your actual internal temperature. When a converted value falls between two Gas Mark numbers, round to the nearer mark rather than the lower one, since UK recipes are written expecting that rounding.
Frequently Asked Questions
Is Gas Mark the same across all countries that use it?
The scale is broadly standardised in the UK, but always sanity-check an unfamiliar recipe's gas mark against its stated Celsius or Fahrenheit value if both are given, since regional variations do exist.
Should I always subtract 20°C for a fan oven?
20°C is the most common guideline, but oven manufacturers occasionally suggest a different adjustment (sometimes 10-25°C) in the appliance manual, which takes priority over a general rule.
Why does my food cook differently even after converting the temperature correctly?
Oven calibration, pan material, rack position and even how often the oven door is opened all affect cooking results independently of the temperature conversion itself.
What Gas Mark is a typical cake baked at?
Most cakes bake around Gas Mark 4, which is roughly 180°C or 350°F on a conventional oven — this converter shows the same equivalence when you enter any of the three.