Weights

Construed accurately, 1 ounce equals 28 grams: in practice, the convention is to express an ounce as 25 or 30 grams; either makes the sums easier and you can choose which you like. Because I have now trained myself to think metrically, and therefore have actually formulated recipes in grams and litres and so on, I cannot honestly say which is the convention you should apply here. It makes sense, then, to give all three – the two rough, the one precise – equivalents.