Why is 200°C listed as 400°F when the maths says 392°F?

Because no oven dial has 392 on it. Oven temperatures are set to marked positions, so recipes round to the nearest real setting — 200°C and 400°F are the same instruction in practice, and the 8°F difference is far smaller than the swing of a domestic oven thermostat.

Do I need to change the temperature for a fan oven?

Yes. A fan oven circulates hot air, so it cooks faster at the same dial setting. Reduce the temperature by about 20°C, or 25–30°F, from the conventional figure. A recipe saying 180°C means roughly 160°C in a fan oven.

How many grams are in a cup?

It depends entirely on the ingredient, which is why a single answer is misleading. A cup of water is about 240 g, a cup of plain flour about 125 g, and a cup of caster sugar about 200 g. Grams measure weight and cups measure volume, so any conversion between them needs to know the ingredient.

Why do small weights stay in grams instead of converting to ounces?

Anything under about 8 g rounds to 0.1 oz or less, which is useless in a kitchen. Teaspoons would need a density we do not have — salt is roughly 6 g per teaspoon and ground pepper about 2.3 g, so one conversion factor would misstate one of them by more than double. Correct beats colloquial when the difference is doubling the salt.

Cooking conversions that match a real kitchen

These are rounded the way recipe writers round, not the way a calculator does. 200°C is listed as 400°F, because no oven dial has 392 on it. Weights and volumes snap to amounts you can actually measure with the spoons and jugs you own.

Oven temperatures

Conventional oven, with the fan equivalent and UK gas mark. Fan ovens run hotter at the same setting, so subtract about 20°C.

Celsius	Fan	Fahrenheit	Gas	Typical use
110°C	90°C	225°F	¼	Very slow — meringues, drying
130°C	110°C	250°F	½	Slow — slow-cooked stews
140°C	120°C	275°F	1	Slow
150°C	130°C	300°F	2	Slow — braising
160°C	140°C	325°F	3	Moderate — rich fruit cakes
180°C	160°C	350°F	4	Moderate — most cakes and biscuits
190°C	170°C	375°F	5	Moderately hot
200°C	180°C	400°F	6	Hot — roasting vegetables
220°C	200°C	425°F	7	Hot — roast potatoes, pastry
230°C	210°C	450°F	8	Very hot
240°C	220°C	475°F	9	Very hot — pizza, bread

Weight

Grams to ounces and pounds. Amounts under 8 g stay in grams on purpose — see the note below.

10 g½ oz

25 g1 oz

50 g2 oz

100 g3½ oz

150 g5 oz

200 g7 oz

250 g9 oz

300 g11 oz

400 g14 oz

500 g1 lb

750 g1¾ lbs

1000 g2¼ lbs

Volume

Millilitres to spoons and cups, rounded to amounts you can measure.

15 ml1 tbsp

30 ml2 tbsp

60 ml¼ cup

100 ml⅜ cup

125 ml½ cup

200 ml⅞ cup

250 ml1 cup

500 ml2 cups

750 ml3¼ cups

1000 ml1 quart

Two things most conversion tables get wrong

A cup is not a weight

“How many grams in a cup” has no single answer, and any table giving one is wrong for most ingredients. A cup of water is about 240 g, plain flour about 125 g, caster sugar about 200 g. Grams measure weight, cups measure volume, and converting between them needs to know what is in the cup.

Small weights should stay in grams

Below about 8 g, ounces stop being useful — 3 g is 0.1 oz, which rounds to nothing. Teaspoons would need a density: salt is roughly 6 g per teaspoon and ground pepper about 2.3 g, so a single conversion factor misstates one of them by more than double. Telling someone to double the salt is a real cooking error, so small amounts stay in grams.

Or never convert anything again

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