Free Cooking Temperature Conversion calculator with clear step-by-step results.
Converts between the three scales recipes actually use and adds the fan-oven adjustment. Gas marks are spaced roughly 14 C apart from mark 1 at about 135 C, and a fan oven cooks about 20 C hotter than its dial because moving air raises heat transfer.
Celsius to Fahrenheit
F = C x 9/5 + 32
Gas mark
Gas mark = (C - 135) / 14 + 1
It is the standard rule of thumb. Some manufacturers specify 15 and a few 25, and the difference matters most for delicate bakes - check your oven's manual.
Mark 1 is around 135 C and the two fractional settings below it, one-quarter and one-half, sit near 110 and 120 C. The calculator floors at one-quarter.