How do I scale a recipe?

People type this into search every day: recipe scaler calculator.

The usual answer is “double it.” That works when you want twice as many plates. It fails when you want 10 from a recipe written for 4, and it fails again when you round 62.5 grams to the next spoon.

The recipe scaler uses one ingredient at a time:

original amount × new servings ÷ original servings

Then it rounds to the step you type. The ingredient scales linearly. Cooking times and pot sizes may not. Those are the tool’s assumptions.

This page is a labeled example. It is not a cookbook, and it is not food-safety advice.

A ratio, then a rounding step

The factor is new servings over original servings. 10 ÷ 4 = 2.5. Every ingredient in that recipe uses 2.5 unless you have a reason to treat one of them differently.

USDA safe minimum internal temperatures are about the center of the food, not about multiplying 90 minutes by 2.5. A larger roast can need more time. The recipe scaler will not invent that time.

NIST’s unit pricing work is price over quantity. After you scale the grams, the ingredient price card prices the amount you will actually use.

Example 1: the published 625 units

Here are the calculator defaults:

• original servings: 4
• needed servings: 10
• original ingredient amount: 250 units
• round to nearest: 5 units

Factor: 10 ÷ 4 = 2.5×

Unrounded: 250 × 2.5 = 625

Rounded to 5: 625

Additional servings: 6

250 units can be grams of flour, millilitres of stock, or cups if you insist. The tool does not convert units. It scales the number you typed.

Example 2: half, 1.5×, double, triple, quadruple

Hold 4 original servings, 250 units, and round to 5.

• 2 servings: factor 0.5×. Raw 125. Rounded 125.
• 6 servings: factor 1.5×. Raw 375. Rounded 375.
• 8 servings: factor 2×. Raw 500. Rounded 500.
• 10 servings (default): factor 2.5×. Raw 625. Rounded 625.
• 12 servings: factor 3×. Raw 750. Rounded 750.
• 16 servings: factor 4×. Raw 1,000. Rounded 1,000.

Every one of those lands on a multiple of 5, so rounding does nothing.

Example 3: one plate, and the 62.5-to-65 bump

Hold 4 original, 250 units, round to 5. Need 1 serving.

Factor: 1 ÷ 4 = 0.25×

Unrounded: 250 × 0.25 = 62.5

Rounded to 5: Math.round(62.5 / 5) × 5 = 13 × 5 = 65

The card prints 65, not 62.5. Additional servings: −3.

That 2.5-unit bump is 4% extra on a single plate. Harmless for flour. Less harmless for salt if you scale a teaspoon the same way.

Example 4: what if I change only the rounding step

Hold 4 to 10 and 250 units.

Round to 1: raw 625, rounded 625.

Round to 5 (default): 625.

Round to 10: Math.round(625 / 10) × 10 = 630.

Round to 25: Math.round(625 / 25) × 25 = 625.

630 is the 10-unit step talking. You buy or weigh 5 extra units because the step is coarser than the raw number.

Example 5: the swapped-servings mistake

People type the 10-serving dinner into “original” and the 4-serving card into “needed.”

Original 10, needed 4, amount 250, round to 5.

Factor: 4 ÷ 10 = 0.4×

Raw: 100

Rounded: 100

The card just shrank the recipe. You wanted 625. You measured 100. That is a 525-unit hole, 84% short.

The same swap on a double (8 from 4) would print 125 instead of 500. If the batter looks thin, check which box is the card and which box is the table.

Example 6: yeast at 7 grams, salt at 8 grams

Same 4-to-10 factor of 2.5.

Yeast 7 g, round to 0.5:

Raw: 7 × 2.5 = 17.5

Rounded: 17.5

Salt 8 g, round to 1:

Raw: 20

Rounded: 20

The yeast scaling default is a different path: 5 g of yeast in 500 g of flour, scaled to 1,200 g of flour. Factor 1200 ÷ 500 = 2.4×. Yeast: 5 × 2.4 = 12 g, which the US profile prints as 0.4 oz. Baker’s percent on that card is 1%.

Use yeast-scaling when the flour weight changed and the serving count did not. Use the recipe scaler when the guest count changed.

The baker’s percentage default is 1,000 g flour at 65%: 650 g of the ingredient, printed 22.9 oz on a US display. That 65% is a formula, not a serving scale.

Example 7: a 24-guest pot and a 60-cookie tray

Party pot: 6-serving recipe, 24 guests, 400 units, round to 25.

Factor: 24 ÷ 6 = 4×

Raw: 400 × 4 = 1,600

Rounded: 1,600

Cookies: 24 cookies on the card, 60 wanted, 300 units of dough, round to 25.

Factor: 60 ÷ 24 = 2.5×

Raw: 300 × 2.5 = 750

Rounded: 750

The catering portions default is 45 guests, 350 g main, 200 g sides, 12% buffer, 20% vegetarian: 38.9 lb of main food, 22.2 lb of sides, 51 buffered servings. That tool starts from a per-guest gram, not from a 4-serving card. Use it when you do not have a recipe and you still need a grocery list.

The food waste default year is $1,219.20. Scaling 10% extra “just in case” on every ingredient is how a 625 g line becomes 688 g and the leftover becomes that bill.

Example 8: price the 625 g you just scaled

The ingredient price per weight default is an $8.50 package at 750 g. 180 g used costs $2.04.

Use 625 g from the default scale:

8.50 ÷ 750 × 625 = $7.08

Cost per 100 g: $1.13

Package share: 83.3%

The unit price post is which bag to buy. This card is how much of that bag the scaled recipe eats.

A 20 cm pan to a 24 cm pan on the pan size default is 1.44×, 11.5 scaled servings from 8. Area scales with the square of the diameter. Guest count does not. If you change pans and guests, pick one factor. Do not multiply 2.5 by 1.44 unless both really changed.

The home coffee post is a dose from a bag, the same price-over-grams idea with an 18 g cup.

Nine scales side by side

Open the recipe scaler with the servings on the card and the plates on the table. Scale each ingredient once. If the food is meat, use the USDA temperature chart for doneness, not a multiplied timer. If the leftover pile keeps growing, scale the 10-plate batch back toward 8 and look at the $7.08 line again.