Oven Temperature Chart

Gas marks are not a conversion of anything. They are a fixed scale of oven settings, so the Celsius column below is the published equivalent rather than a calculated one. Only the Fahrenheit column is converted.

A fan circulates hot air instead of letting it stratify, so food receives heat faster at the same air temperature. The convention is to set a fan oven about 20 °C below the conventional figure to get the same result in the same time.

This is a manufacturer convention rather than a physical constant, and 20 °C is a round number chosen for convenience. Some ovens are better matched at 15 °C and some at 25 °C, so treat the first bake in an unfamiliar oven as a calibration run.

The adjustment is also the single most common cause of a recipe failing across borders. A UK recipe saying "180 °C" usually means conventional, so setting a fan oven to 180 °C overshoots by about 20 degrees and produces a cake that is dark outside and raw in the middle.

The exact conversion of 180 °C is 356 °F, and every American oven dial says 350 °F. That 6-degree gap is smaller than the swing of a domestic oven thermostat, which typically cycles ±10 °C around its set point, so the rounding is harmless.

What is not harmless is the oven itself. Domestic ovens are frequently 10 to 20 degrees out of calibration, and hot spots within a single oven can differ by more again. An oven thermometer costs very little and tells you more than any conversion chart can.