Tablespoons to teaspoons:
multiply by three, and know when that is wrong

The rule: one tablespoon holds three teaspoons

A recipe asks for 2 tablespoons of oil and your only clean spoon is the small one. Or you want to measure 5 tablespoons of sugar and the tablespoon is missing from the drawer. In both cases the conversion is the same: a tablespoon is three teaspoons.

The factor of three holds in US customary measures, where a tablespoon is half a fluid ounce and a teaspoon is a sixth of one. Metric kitchens round it to 15 ml and 5 ml, which keeps the ratio at exactly three.

It helps to hold a picture of the sizes. Fill a teaspoon three times into a tablespoon and it is level full; the larger spoon is not just a bit bigger but three times the volume. That is why substituting the wrong spoon is not a small error, and why a recipe that calls for a teaspoon of chilli powder behaves very differently with a tablespoon.

A quick reference table

Handy anchors to remember are 3 teaspoons to a tablespoon, 4 tablespoons to a quarter cup and 16 tablespoons to a cup. Everything in the table can be rebuilt from them in a few seconds, and the cup row is a good check that you have the multiplication right: 16 × 3 gives 48.

A second example shows the rule at work in a larger recipe. A marinade for four portions uses 2½ tablespoons of oil, 1 tablespoon of lemon juice and 1½ teaspoons of salt. Working everything in teaspoons gives 7½ + 3 + 1½ = 12 teaspoons, which is 4 tablespoons, or a quarter cup of liquid and salt together. Doubling for eight portions is then 24 teaspoons, or half a cup.

Fractions and awkward amounts

Scaling a recipe is where most conversion errors happen. Halving 1 tablespoon gives 1½ teaspoons, and a third of a tablespoon is exactly 1 teaspoon. A recipe asking for 2½ tablespoons becomes 7½ teaspoons.

• Half a tablespoon is 1½ teaspoons, which is a level teaspoon and a half-full one.
• A quarter of a tablespoon is ¾ teaspoon, so a generous ½ plus a small ¼.
• A tablespoon plus 2 teaspoons is 5 teaspoons.
• For very small amounts, such as a pinch of salt or a dash of spice, the spoon rule is a guide and not a precise measure.

When a recipe uses grams for the main ingredients but spoons for raising agents or spices, convert only the spoon amounts and leave the grams alone. A tablespoon of baking powder in place of a teaspoon is three times too much and will ruin a cake, which makes this the conversion worth double-checking.

Spoons are not the same size everywhere

The factor of three is stable in the US and in countries that use a 15 ml tablespoon and a 5 ml teaspoon. Australia is different: its tablespoon is 20 ml, so it holds four teaspoons. A recipe written in Australia that calls for 2 tablespoons means 40 ml, not 30.

Older British recipes may use an imperial spoon of slightly different size, so a vintage cookbook needs a little caution. If a recipe is from a different region, look for a note on spoon size, or check whether it also gives millilitres, which removes the ambiguity.

When volume is the wrong question

The tablespoon-to-teaspoon rule is exact as a volume, but cooking is often about weight. A level tablespoon of table salt, a heaped tablespoon of flour and a tablespoon of honey weigh very different amounts, and the same volume of fine and coarse salt differs again because the crystals pack differently.

For most home recipes this is fine, since the author measured with spoons. It matters when you swap one ingredient for another that has a different density, or when a recipe moves between a spoon-based and a gram-based version. Salt is the standard example: a teaspoon of fine table salt is noticeably saltier than a teaspoon of flaky salt, so substituting one for the other by spoon alone can change the seasoning a lot.

Medicine is a stricter case. Household spoons are not accurate dosing instruments, and anyone giving liquid medicine should use the oral syringe or cup supplied with it and follow the label or the pharmacist's instructions, rather than converting from a kitchen spoon.

Measuring well with spoons

1. 1Use real measuring spoons rather than cutlery. A dinner spoon can hold anywhere from 7 to 15 ml.
2. 2Level the spoon with the back of a knife unless the recipe says heaped.
3. 3For liquids, fill to the brim without letting a dome rise above the edge.
4. 4Measure sticky ingredients such as honey after a light coating of oil on the spoon so they slide out.
5. 5Weigh when you can. A spoon of flour can differ by 20 per cent depending on how it was scooped, while grams are the same every time.