Make a recipe bigger or smaller: every amount, worked out

How the page counts

• One number for the whole recipe. What you want to make, divided by what the recipe makes. Every amount is multiplied by it.
• The sums are exact fractions. Nothing is rounded along the way.
• Each new amount is shown as a whole number and a fraction: 9/8 is shown as 1 1/8.
• When the answer is not a half, a third, a quarter or an eighth, the page also shows it as a number with two places, and names the nearest half, third, quarter or eighth.
• Amounts can be typed as 2, 3/4, 1 1/2, 0.5 or 2,25.
• A line with no amount is left out. A line with no name is called Ingredient 1, Ingredient 2 and so on.
• The page only multiplies. The measure (cups, spoons, grams) stays the one you typed.

Examples, worked by hand.

• The recipe makes 12 and you want 18: 18 ÷ 12 = 1 1/2. Flour, 3/4 cup: 3/4 × 1 1/2 = 1 1/8 cups. Eggs, 2: 2 × 1 1/2 = 3. Salt, 1/2 teaspoon: 3/4. Milk, 1 1/3 cups: 2 cups.
• Half a recipe (times 1/2): 3/4 becomes 3/8. 3 becomes 1 1/2. 1/3 becomes 1/6, which is about 0.17, a little more than 1/8.
• The recipe makes 6 and you want 4: 4 ÷ 6 = 2/3. Then 1 1/2 becomes 1, 2 becomes 1 1/3, 1/2 becomes 1/3, and 1/4 becomes 1/6.
• The recipe makes 8 and you want 20: 20 ÷ 8 = 2 1/2. Then 2/3 becomes 1 2/3, 0.75 becomes 1 7/8, and 1/3 becomes 5/6, which is about 0.83, a little less than 7/8.
• Three times a recipe: 1/4 becomes 3/4, 2/3 becomes 2, and 1 1/2 becomes 4 1/2.

The examples are made up. A program checks them, and 400 made-up recipes done a second way, every time the page is built.

Where fractions trip people up

• From 12 to 18 is 6 more, but the amounts are not 6 more. They are multiplied: 18 ÷ 12 = 1 1/2.
• Half of 3/4 is 3/8. To halve a fraction, the bottom number doubles and the top stays.
• Double 2/3 is 1 1/3. Only the top number doubles: 4/3, which is 1 1/3. Doubling both gives 4/6, and 4/6 is 2/3 again.
• Half of a half is a quarter, not a whole: 1/2 × 1/2 = 1/4.
• Every line gets the same sum, the salt and the water too. A recipe with some lines changed and others not is a different recipe.
• Some answers land between the marks. Half of 1/3 is 1/6. The page shows it as about 0.17, a little more than 1/8.

What this page does not know

• It does not change one measure into another. Teaspoons stay teaspoons and cups stay cups, however large the number gets.
• It does not know cooking times, oven heat or pan sizes, and it does not multiply them. A bigger or smaller batch can cook differently; the page cannot say how.
• It does not know what can be split. Half of 3 eggs is 1 1/2 on the page; what to do with half an egg is the cook's call.
• It does not know how a recipe will turn out at another size. Baking in particular can change.
• It is for cooking, not for mixing baby formula or medicine. Those are mixed the way the label, the pharmacy or the doctor says, not by a sum from this page.
• It knows nothing about food allergies, nutrition or how much anyone eats. A serving is whatever the recipe calls a serving.
• It holds up to 20 recipes of up to 12 lines on this device, and they do not move to another phone or computer by themselves.

If food is the hard part

• On this site: When you need food lists the kinds of food help there are, and who to call.
• On this site: Shopping list adds up the total before the register.