How much lower should I set a fan oven?

The standard baking-industry rule of thumb is to lower a fan (convection) oven's set temperature by about 20°C (or 25°F) compared to a conventional oven, because the moving air cooks food faster and more evenly at the same air temperature. This is the adjustment used throughout UK recipe publishing and appears on most oven dials themselves.

Gas mark is a UK oven-temperature scale historically used on gas ovens, running from 1/4 (very cool, 110°C) to 9 (very hot, 240°C). It doesn't convert to Celsius by a fixed formula — it's a standardized lookup table, which is why this tool matches your temperature to the nearest published gas mark band rather than calculating one.

Why does my converted Fahrenheit number look like an odd round figure?

Recipe temperatures are usually written as round numbers in their original unit (180°C, 350°F, and so on), and converting between °C and °F rarely lands on another round number — 180°C converts to exactly 356°F, for instance, which most recipes would round to '350°F' in practice.

Which oven type should I select if I'm not sure?

If your recipe doesn't specify, most classic and older recipes (and most US recipes) assume a conventional oven; UK recipes increasingly specify both. If your oven only has a fan setting and the recipe doesn't say, using the fan-adjusted temperature this tool provides is the safer default.

Oven Temperature Converter

Convert oven temperatures between Celsius, Fahrenheit and UK gas mark, with a fan/convection oven adjustment and the full gas mark reference chart.

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Formula: °F = °C × 9/5 + 32; fan oven = conventional − 20°C (−25°F); gas mark matched to the nearest entry in the standard UK conversion chart

Worked examples

180°C conventional recipe temperature
The most common baking temperature, showing both the conventional and fan-adjusted equivalents.
350°F conventional recipe temperature
A US recipe given in Fahrenheit, converted to Celsius and a UK gas mark.
160°C fan oven setting, converting back to conventional
Starting from a fan-oven setting instead of a conventional one — the tool works out the equivalent conventional temperature first.

What this calculator does

Recipes from different countries and eras use different oven temperature scales — Celsius, Fahrenheit, or the UK's gas mark system — and modern fan (convection) ovens are typically set several degrees cooler than a conventional oven for the same actual cooking result. This tool converts between all of these at once: enter a temperature in either °C or °F, specify whether it's a conventional or fan oven setting, and get every equivalent plus the nearest matching gas mark.

Celsius and Fahrenheit conversion

The conversion between Celsius and Fahrenheit is a fixed formula: °F = °C × 9/5 + 32. This part is exact — there's no approximation involved, just the standard temperature-scale relationship used worldwide.

What gas mark actually is

Gas mark is a temperature scale that predates precise oven thermostats, historically used on UK gas ovens and still printed on many British recipes today. Unlike the Celsius-to-Fahrenheit relationship, gas mark isn't derived from a formula — it's a standardized lookup table, running from 1/4 (very cool, around 110°C) up to 9 (very hot, around 240°C), as published by UK culinary references including BBC Good Food. Because it's a table rather than a formula, this tool matches your entered temperature to the closest published gas mark band rather than calculating one directly.

The fan oven adjustment

Fan (convection) ovens circulate hot air, which cooks food faster and more evenly than a conventional oven at the same air temperature. The standard adjustment used throughout baking references and printed on many oven dials themselves is to set a fan oven about 20°C (or roughly 25°F) cooler than the conventional-oven temperature a recipe calls for. This tool applies that adjustment in both directions — starting from either a conventional-oven temperature or an already-adjusted fan-oven setting — so you always see both numbers regardless of which one your recipe or your oven's dial actually shows.

Using the reference chart

The gas mark table included with every result shows the full standard range from 1/4 through 9, alongside each mark's approximate Celsius, Fahrenheit and general heat description (cool, moderate, hot, and so on). This is useful beyond just converting a single number — it gives context for how hot a "moderate" oven actually is compared to a "hot" one, which is handy when a recipe describes temperature qualitatively rather than numerically.

Limits

Oven thermostats vary in real-world accuracy — many home ovens run several degrees hotter or cooler than their dial indicates, and the fan-oven adjustment is a general rule of thumb rather than a measurement of your specific oven. Gas mark's band-based nature means the "nearest" match can be a meaningful distance from your exact input at the edges of each band. This is a kitchen reference tool, not food-safety advice — always verify doneness with a food thermometer for meat, poultry and other temperature-sensitive dishes rather than relying on oven temperature alone.

Frequently asked questions

How much lower should I set a fan oven?: The standard baking-industry rule of thumb is to lower a fan (convection) oven's set temperature by about 20°C (or 25°F) compared to a conventional oven, because the moving air cooks food faster and more evenly at the same air temperature. This is the adjustment used throughout UK recipe publishing and appears on most oven dials themselves.
What is a gas mark?: Gas mark is a UK oven-temperature scale historically used on gas ovens, running from 1/4 (very cool, 110°C) to 9 (very hot, 240°C). It doesn't convert to Celsius by a fixed formula — it's a standardized lookup table, which is why this tool matches your temperature to the nearest published gas mark band rather than calculating one.
Why does my converted Fahrenheit number look like an odd round figure?: Recipe temperatures are usually written as round numbers in their original unit (180°C, 350°F, and so on), and converting between °C and °F rarely lands on another round number — 180°C converts to exactly 356°F, for instance, which most recipes would round to '350°F' in practice.
Which oven type should I select if I'm not sure?: If your recipe doesn't specify, most classic and older recipes (and most US recipes) assume a conventional oven; UK recipes increasingly specify both. If your oven only has a fan setting and the recipe doesn't say, using the fan-adjusted temperature this tool provides is the safer default.

These calculators give general estimates from published formulas. They are not medical advice and do not account for your individual health; talk to a qualified professional before changing your diet or training.