Convert any oven temperature: °C, °F, fan, and gas mark

180°C is 350°F, or gas mark 4. On a fan or convection oven, set it to 160°C instead — the fan moves hot air across the food, so it cooks as though the oven were 20°C hotter than the dial says.

Yes, for almost everything. A fan oven at the recipe's stated temperature browns the outside before the middle is done. The rule is to drop 20°C (about 25°F) from any conventional temperature. The exceptions are things you want aggressively dried or crisped — roast potatoes, some pizzas — where cooks often keep the fan temperature high on purpose.

Gas marks were defined by the burner settings on British gas ovens rather than derived from a temperature formula. Marks 1 through 9 step up in 25°F increments, but the fractional marks below 1 (¼ and ½) were added underneath for slow cooking and break the pattern. That is why a gas mark has to be looked up on a chart rather than calculated.

Usually less accurate than you would like. Domestic ovens routinely run 10–20°C off their setting, and they swing above and below the target as the thermostat cycles. If your bakes are consistently over- or under-done at the correct temperature, a cheap oven thermometer will tell you the offset in one session.

Not directly — an air fryer needs both a temperature and a time adjustment. Use the air fryer converter for that, which applies the 20°C drop plus the roughly 20% shorter cooking time.