Cooking Calculators

A Guide to Cooking Calculators

Cooking is the one area where ignoring the arithmetic usually works fine, right up until it does not. A stew survives a loose measurement. Bread, pastry and anything roasted do not, because they depend on ratios and on time that scales in a way most people guess wrongly.

The twenty calculators here handle the conversions and ratios that matter, and they are built around one fact that runs through the whole category: volume measures are unreliable for dry ingredients, and weight is not.

Cups, grams and why they disagree

The Cups to Grams Calculator and Grams to Cups Calculator are the two directions of the conversion people need most, and both ask what the ingredient is, because there is no single answer.

A cup is a volume. A gram is a weight. Converting between them requires the density of the specific ingredient, and the spread is enormous: a cup of flour is around 120 g, a cup of granulated sugar around 200 g, and a cup of honey around 340 g. Any tool offering a single cups-to-grams factor is averaging over ingredients that differ by a factor of three.

Flour is worse still, because how you fill the cup changes the answer. Scooping directly from the bag compacts the flour and can add a quarter more than spooning it in and levelling off. That is why a recipe written in cups and followed exactly can still produce dry bread, and why the dedicated Flour Conversion Calculator distinguishes flour types, which differ from each other as well.

The Sugar Conversion Calculator handles granulated, caster, icing and brown sugars, which do not share a density, and the Butter Conversion Calculator covers sticks, tablespoons, cups and grams, where the American stick is a unit with no equivalent anywhere else.

General measurement

The Cooking Measurement Converter is the catch-all for the rest, and the Tablespoon to Teaspoon Calculator handles the small measures, which carry a trap: the Australian tablespoon is 20 ml rather than 15 ml, so a recipe from one country scaled by spoon counts from another is out by a third on that ingredient.

Scaling a recipe

The Recipe Converter and Recipe Scaling Calculator adjust quantities for a different number of servings, and they flag the ingredients that should not be scaled linearly.

That caveat is the useful part. Doubling a recipe doubles the flour and the liquid, but seasoning, spice and leavening do not scale proportionally, and nor does cooking time. Salt scales close to linearly, strong spices less so, and baking powder in a doubled cake will over-rise if simply doubled. The calculator separates the ingredients it scaled directly from the ones you should taste and adjust.

Baking

Four calculators for the part of cooking that behaves like chemistry. The Bread Hydration Calculator works in baker's percentages, where every ingredient is expressed as a proportion of the flour weight. That convention exists because it makes a recipe scalable to any quantity and comparable to any other recipe, which cups cannot do. A 65 percent hydration dough and a 80 percent one behave completely differently in the hand, and the number tells you which you are about to make.

The Baking Pan Conversion Calculator adjusts for a different tin, which is an area and depth problem rather than a diameter one: a 9-inch round pan has about 27 percent more area than an 8-inch, so the same batter bakes shallower and faster.

The Oven Temperature Converter handles Celsius, Fahrenheit and gas marks, and accounts for fan ovens, which run effectively hotter and need a reduction of around 20 °C. The Yeast Conversion Calculator converts between fresh, active dry and instant yeast, which are not interchangeable by weight.

Roasting and cooking times

Two calculators for the question that ruins dinners. The Roast Cooking Time Calculator and Turkey Cooking Time Calculator work from weight to time at a given temperature and target doneness.

Both make the same point: cooking time does not scale with weight. Heat has to travel to the centre, and that depends on the thickness rather than the mass, so a joint twice as heavy needs considerably less than twice the time. Scaling linearly is the single most common roasting error and it overcooks the outside badly. Both calculators also give a target internal temperature, which is the only reliable test, and include resting time, which continues to raise the centre by several degrees after the oven.

Portions

Three calculators for cooking the right amount. The Meat Portion Calculator works from guest count and accounts for bone-in weight, where a substantial share of what you buy is not what you serve. The Pasta Portion Calculator handles dry to cooked weight, which roughly doubles, and the Rice Water Ratio Calculator gives the liquid for the rice type and method, which differ more than most recipes admit.

Drinks

The Coffee Ratio Calculator works in the coffee-to-water ratios that brewing methods are specified in, from the strong ratios of espresso through to filter. The Cocktail Ratio Calculator scales a drink to a batch, which is the case where small measuring errors multiply and become noticeable.

Reading a recipe from another country

Most cooking failures involving a written recipe come from an unstated convention rather than from technique, and there are five worth checking before you start.

The cup is not one size. The US cup is about 237 ml, the metric cup 250 ml, and older British recipes use an imperial cup of 284 ml. A recipe scaled across those loses or gains a fifth.

The tablespoon is not one size either, as above: 15 ml almost everywhere and 20 ml in Australia.

The ounce is two different units. A fluid ounce is a volume and an ounce is a weight, and they are not related by any fixed factor, because that depends on the ingredient. The US fluid ounce and the imperial fluid ounce also differ by about four percent.

Flour is not one ingredient. Plain, bread, self-raising and cake flour differ in protein and in density, and self-raising already contains leavening, so substituting it without removing the baking powder doubles the rise.

Oven temperatures assume a conventional oven unless stated. A fan oven at the written temperature cooks faster and drier, and the usual correction is a 20 °C reduction.

Each of those is the kind of mistake that produces a result you cannot diagnose from the finished dish, which is why checking the convention is worth more than adjusting the method afterwards.

The habit that fixes most of it

Buy a scale and use it for anything baked.

Everything in this category is a workaround for the fact that recipes are written in volume and cooking in ratios. Weighing removes the whole problem: it is faster than measuring cups, it uses fewer washing up items, and it makes a recipe reproducible instead of approximately repeatable. Professional baking is done entirely by weight for that reason.

Where you cannot weigh, the conversions above are the next best thing, and they are more honest than a single factor because they ask what the ingredient is. But the conversion is always an estimate of something a scale would simply tell you.

The exception is liquid, where volume is the natural measure and a jug is as accurate as a scale. Water, milk and stock are close enough to one gram per millilitre that the distinction does not matter, which is why liquid measures in recipes cause far fewer problems than dry ones do.