Quick tips

• Divide new by old. The factor is party size ÷ recipe size. 18 ÷ 6 = 3, and 21 ÷ 12 = 1¾.
• Multiply, never add. Twelve more guests doesn't mean twelve more grams: every amount grows by the same factor.
• Split the factor. ×2½ is ×2 plus half again: 200 g becomes 400 + 100 = 500 g.
• Tidy the spoons. 3 tsp = 1 tbsp, so 6 tsp is 2 tbsp. Bigger units are easier to measure.
• Check with eggs. Eggs come whole: if the egg count isn't a whole number, check your factor.