Oven Temperature Converter

Why fan-forced runs 20°C cooler

A conventional oven heats by radiation from the elements and slow convection, so the air near the food sits in a warm, still blanket. Switch the fan on and that blanket is stripped away every second, which moves heat into the food far more efficiently. The oven has not become hotter, but the food behaves as if it had. Australian recipe writers settle that difference at 20°C: a dish that wants 180°C conventional wants 160°C fan-forced. The Women's Weekly Test Kitchen allows 10 to 20°C, because a gentle fan in a large oven does less work than a strong one in a small oven, which is why the converter lets you pick a 10°C offset if your baking says so.

Which setting does the recipe mean?

• Australian recipesfrom taste.com.au, the Women's Weekly, Coles and Woolworths magazines usually print both: “180°C (160°C fan-forced)”. If only one figure is given, it is conventional.
• British recipeswrite “180°C / 160°C fan / gas 4”, and older books give only gas marks. Gas mark 4 is 180°C conventional.
• American recipes are always Fahrenheit and always conventional. Convert to Celsius first, then take 20°C off for the fan. 350°F is the workhorse: 180°C, or 160°C fan-forced.
• Packet instructions in Australia now give both settings; if the packet only lists one, treat it as conventional.

When to use the fan, and when not to

Moving air is your friend for roasting, for potatoes and vegetables you want crisp, for biscuits and sausage rolls spread across two or three trays, and for anything with pastry. It is less kind to delicate batters. A sponge, a pavlova, a meringue, a soufflé or a cheesecake sets better in still air, so if your oven offers a conventional setting, use it for those and accept a slightly longer bake. If it is fan only, drop the temperature, put the tin in the centre and resist opening the door for the first two-thirds of the time.

Time changes too

Even at the lower setting, a fan-forced oven finishes most things 10 to 15 per cent sooner. A 40-minute cake is often done at 35, and a two-hour roast at an hour and three-quarters. Check early, then trust the skewer or a probe thermometer rather than the clock: chicken is safe at 74°C in the thickest part, a medium roast lamb at 65°C after resting.

Check what your oven actually does

Dials drift. A ten-dollar oven thermometer left on the middle shelf will often show a domestic oven running 10 to 20°C hot or cold, and fan-forced ovens have a hot spot near the back wall. If your baking is reliably pale or reliably scorched at the converted setting, adjust by 10°C and write the correction on a note inside the cupboard door. Converting to the air fryer instead? Same idea, bigger drop: the calculator for that is separate.