Fraction Calculator guide
Working with Fractions in Recipes
To scale a recipe measurement, multiply it by the scaling factor as a fraction. Two thirds of ¾ cup is ¾ × ⅔ = ½ cup. Converting cups to tablespoons first often makes awkward fractions much easier, since one cup is 16 tablespoons.
Scaling is multiplication
Whenever you resize a recipe, you multiply each measurement by the same fraction.
Halving means multiplying by ½. Doubling means multiplying by 2. Going from a recipe for 6 to one for 4 means multiplying by ⅔.
So "two thirds of ¾ cup" is ¾ × ⅔. Multiplying straight across gives 6/12, which simplifies to ½ cup.
That is the calculation loaded into the calculator on this page.
Convert to tablespoons when it gets awkward
Some scaled amounts do not land on anything you can measure. A third of ¾ cup is ¼ cup, which is fine. But a third of ½ cup is ⅙ cup, and no measuring cup has a sixth on it.
The fix is to convert to tablespoons, because a cup is 16 tablespoons — a number that divides much more agreeably.
⅙ of a cup is 16 ÷ 6 = 2.67 tablespoons, which is 2 tablespoons plus 2 teaspoons. That you can measure.
Cup conversions worth knowing
| Cups | Tablespoons | Teaspoons |
|---|---|---|
| 1 | 16 | 48 |
| ¾ | 12 | 36 |
| ⅔ | 10⅔ | 32 |
| ½ | 8 | 24 |
| ⅓ | 5⅓ | 16 |
| ¼ | 4 | 12 |
| ⅛ | 2 | 6 |
Halving awkward amounts
These are the ones that come up constantly when halving a recipe:
- Half of ¾ cup = ⅜ cup = 6 tablespoons
- Half of ⅔ cup = ⅓ cup = 5 tablespoons + 1 teaspoon
- Half of ⅓ cup = ⅙ cup = 2 tablespoons + 2 teaspoons
- Half of ¼ cup = ⅛ cup = 2 tablespoons
- Half of 1 tablespoon = 1½ teaspoons
Weighing is easier than fractions
If you have kitchen scales, most of this disappears. Weights scale by straight multiplication with no awkward fractions at all — 150g halved is 75g, and there is nothing to look up.
Volume measurements are also less accurate to begin with. A cup of flour can vary by 20% depending on whether it was scooped or spooned, which is far more error than any rounding you would do while scaling.
For baking in particular, switching to weights solves the fraction problem and the accuracy problem at once.
The things that do not scale cleanly
Not every ingredient should be multiplied by the same factor, and this is where arithmetic stops being enough.
Eggs come in whole units. Beat one, weigh it, and use the fraction you need — a large egg is roughly 50g without its shell. For savoury cooking, round to a whole egg.
Salt and strong spices should be scaled to about 75% of what the maths says, then tasted and adjusted. Seasoning intensity does not rise in a straight line.
Baking powder and bicarbonate should be scaled, but cautiously. Too much makes a cake rise quickly and then sink.
Cooking time does not scale at all. Judge by temperature and appearance, not by multiplying the minutes.
