Conventional vs. Fan (Convection) Ovens
A conventional oven heats food using stationary heating elements at the top and bottom. Heat distribution can be uneven — the bottom tends to be hotter, and different oven zones cook at slightly different rates. This is why recipes say "rotate halfway through baking."
A fan-forced (convection) oven adds a fan that circulates hot air, creating even temperatures throughout. This reduces hot spots but also increases the effective cooking temperature. The standard adjustment is: reduce the recipe temperature by 20°C (35°F), or reduce cooking time by 10–15% while keeping the same temperature.
Gas Mark Quick Reference
Gas marks are the temperature control system for gas ovens, used primarily in the UK, Ireland, and Australia. Each Gas Mark number roughly equals a 14°C / 25°F increment above 135°C (275°F). The most common baking temperature, 180°C (350°F), corresponds to Gas Mark 4.