Kitchen Conversions - My Kitchen Answers

Most conversion problems aren’t really about arithmetic. They’re about the fact that a cup isn’t the same size in every country, a tablespoon isn’t either, and a cup of flour can weigh anywhere from 120g to 160g depending on how you filled it.

Here are the numbers you’ll actually need, and the traps worth knowing about. For a quick one-off conversion, the Kitchen Measurement Converter does the arithmetic for you, including ingredient-specific weight conversions.

Common ingredient weights

These are King Arthur Baking’s figures, which are the closest thing to a standard reference for US baking.

Ingredient	1 cup
All-purpose / plain flour	120g (4¼ oz)
Granulated sugar	198g (7 oz)
Brown sugar, packed	213g (7½ oz)
Confectioners’ / icing sugar, unsifted	113g (4 oz)
Butter	227g (8 oz) — 2 US sticks

One US stick of butter is 113g (4 oz), which is ½ cup or 8 tablespoons. If you’re working from a UK or Australian block, a 250g block is about two sticks plus a little over.

Why sources disagree about flour

You’ll see 120g, 125g and 142g all quoted for a cup of flour. They’re not errors — they reflect different measuring habits. King Arthur uses 120g. The USDA lists 125g. America’s Test Kitchen uses 142g, which they arrived at by averaging how dozens of volunteers actually scooped flour.

The practical takeaway: a flour weight only means something alongside the source that wrote the recipe. If a recipe gives grams, use its grams.

Cups are not the same everywhere

Cup	Volume
US “legal” cup (what most US recipe writers mean)	240 ml
US customary cup (8 US fl oz exactly)	236.6 ml
Metric cup — Australia, New Zealand, Canada	250 ml

The gap between a US cup and a metric cup is about 4%. That’s negligible for a cup of stock and it matters for a cup of flour in a small bake.

What about a UK cup?

There isn’t one, in any current legal sense. Modern British recipes are written in grams, and cup measures sold in the UK today are metric 250 ml.

If a UK recipe asks for cups, use 250 ml. If it’s an old recipe, be careful — a historical British “breakfast cup” was half an imperial pint, about 284 ml. When in doubt with older British baking, find a version written in grams.

The Australian tablespoon problem

This is the conversion trap most worth knowing, and it catches people constantly.

Country	1 tablespoon	Teaspoons per tablespoon
US, UK, New Zealand	15 ml	3
Australia	20 ml	4

A teaspoon is 5 ml everywhere. It’s the tablespoon that differs.

There’s a second layer to this. Australian baking authorities point out that many measuring spoons sold in Australian shops are 15 ml, while Australian recipes are written for the 20 ml tablespoon. For flour or sugar the 5 ml difference is trivial. For baking powder, bicarbonate of soda or yeast it’s a 33% error, which is enough to ruin a bake.

If you’re in Australia and your bakes keep coming out oddly, check what your tablespoon actually holds.

Oven temperatures

Fahrenheit	Celsius (conventional)	Fan / convection	Gas mark
325°F	160°C	140°C	3
350°F	180°C	160°C	4
375°F	190°C	170°C	5
400°F	200°C	180°C	6
425°F	220°C	200°C	7

The published Celsius figures are conventional roundings rather than exact conversions — 350°F is technically 176.7°C, but every UK and Australian oven is marked 180°C and every recipe assumes it. Use the roundings. Fan ovens generally run about 20°C hotter than the dial suggests, which is why the fan column is lower.

Fluid ounces and weight ounces are different things

A fluid ounce measures volume. An ounce measures weight. They get confused because a US fluid ounce of water happens to weigh almost exactly one ounce — a coincidence that holds for water and nothing else.

1 US cup = 8 US fluid ounces
1 US fluid ounce = 29.57 ml
1 imperial (UK) fluid ounce = 28.41 ml — about 4% smaller
1 ounce by weight = 28.35 g

A cup of flour is 8 fluid ounces by volume but only about 4¼ ounces by weight. And in an older British recipe, “8 oz” is almost always a weight, not a volume.

Why bakers weigh flour

Because measuring flour by volume is genuinely unreliable, and the size of the error surprises people.

King Arthur measured the difference: flour spooned lightly into a cup gives about 120g, while flour packed densely into the same cup can reach 160g. That’s an extra third of a cup of flour in a measurement that looks identical. America’s Test Kitchen found up to a 20% swing between scooping and spooning.

If you don’t have a scale, the recommended method is: fluff the flour in the bag, spoon it lightly into the cup, then level it with a straight edge. Never dip the cup into the bag.

Scaling a recipe up or down

The bulk ingredients — flour, sugar, fat, liquid — scale linearly if you work by weight. Several other things don’t, and this is where scaled recipes go wrong.

Baking time. No linear relationship at all. Halving a recipe can take anywhere from 5% to 50% less time. Start checking at half the original time and judge by browning and edges pulling from the pan, not the clock.
Pan size. Scale by the pan’s bottom area, not its name. An 8-inch square and a 9-inch round are both about 64 square inches and interchangeable. A 9×13 is 117 square inches.
Batter depth. Even at the same area, a deeper batter bakes differently. The same batter in a 10-cup Bundt takes roughly 30% longer than in a 9×13.
Anything relying on evaporation. Double a stew and you have twice the liquid but the same pan surface, so it won’t reduce the same way. Use a wider pot or cook it longer uncovered.
Rice and grains. Don’t assume the cooking liquid always scales perfectly with the amount of grain. Evaporation, pot size and cooking method affect how much liquid is needed, so a larger batch may not require exactly twice the liquid. Follow the ratios and method for the particular grain and cooking method you’re using.
Eggs. Not divisible by count. A large egg out of the shell is about 50g — whisk one and weigh out half.

One useful exception: individual items like cookies, muffins and cupcakes scale safely with no change to time or temperature, because the size of each piece hasn’t changed. For a shortcut on any of this (servings, pan-size math, or converting the scaled amounts to metric), see the Recipe Scaling Calculator.

You’ll also see advice to scale salt and spices sub-linearly — using 1.5x when doubling, for instance. We couldn’t verify that from any authoritative source, so treat it as cook’s folklore rather than a rule. Taste and adjust instead.