How much to buy: portions, yields and scaling recipes

Purchase amounts for the week's main ingredients worked out from people, portions and USDA yield figures, and one recipe scaled to your household with what does not scale in a straight line.

1. Serving size, portion and a starting amount Understand

Three amounts get confused when working out what to buy. A serving size is a standard amount of a food used for labels and guidance, such as a cup or an ounce. A portion is how much of a food one person is served or eats at one meal, and it changes from meal to meal. The National Institute on Aging's page on portions draws the line this way, and says a portion can be bigger than a serving: the cereal box says one cup and you pour one and a half (NIA, How Much Should I Eat?).

The serving size on a Nutrition Facts label is a third thing. FDA's page on serving size says that by law it is based on the amount people typically eat, not on how much they should eat, and that one package can hold more than one serving (FDA, Serving Size on the Nutrition Facts Label). A label serving tells you how the package's numbers were counted. It is not an instruction for how much to cook, and Your meal list covers the rest of the label (the Nutrition Facts label).

For buying, what matters is the portion your household actually eats. Until you have measured it, you need a starting figure.

Reference portions

This manual uses the serving examples printed with the Dietary Guidelines for Americans, 2025-2030 as reference portions: starting amounts per person per meal for the buy calculator, which you replace with your own once you know them (Dietary Guidelines 2025-2030, Daily Servings by Calorie Level). The figures are current federal guidance; using them for purchase arithmetic is this manual's choice.

The grain serving example names whole grains. The calculator applies the same ½ cup to white rice and spaghetti because it is a starting amount for buying, not a statement about which grain to eat. This manual gives no diet; the food-group check in Your meal list is an observation about a list (food groups).

How much a person eats depends on age, size, activity, appetite and the rest of the meal, and it changes from day to day. To find your household's real portion, weigh or measure what is cooked for one meal and what is left after it, for two or three meals of the same dish. Test it

2. As purchased and what you eat: yields

Food is bought in one form and eaten in another. The as-purchased amount (written AP) is what you pay for: a pound of broccoli with its stalks, a pound of raw chicken thighs, a pound of dry rice. The edible portion (EP) is what is left to eat after trimming, peeling, coring and cooking. Between them sits the yield: how much edible food one unit as purchased gives. Raw weight is not cooked weight. Meat and poultry lose water and fat as they cook, vegetables lose stems and peel, and rice and pasta take up water and grow.

USDA publishes yields in the Food Buying Guide for Child Nutrition Programs, written for school and child-care kitchens (Food Buying Guide, Introduction). Its introduction says the figures are averages from good-quality food prepared with a minimum of waste, and that yields change with the food's quality and condition, storage, equipment, cooking method and time, the form served and the serving utensil. Its yield tables give, for each form of a food, the servings one pound gives and lines such as "1 lb AP = 0.81 lb ready-to-cook". Ready to cook means trimmed and prepared, before cooking.

The figures come from the guide's sections on meats (Section 1), vegetables (Section 2), fruits (Section 3) and grains (Section 4). The guide counts produce and grains in quarter-cup servings, so the calculator divides by four: broccoli's 10.20 quarter-cup servings per pound become 2.55 cups. The meat rows count 1 oz servings of cooked lean meat, so 10.07 servings is 10.07 oz.

So a pound of boneless chicken thighs gives about 10 oz to eat, not 16, and a pound of dry rice gives seven and a half cups cooked. That is why the arithmetic below divides by the yield instead of buying "a pound for a pound".

A yield applies when you buy a food in one form and eat it in another. A bag of washed, ready-to-eat salad greens or a bag of florets is already in the form you eat; the guide's appendix on its yield column says not to use that column when the recipe uses the food in the same form as the purchase unit (Food Buying Guide, Appendix B). For those, the package weight is the edible weight, and the question is only how many meals the package covers.

3. The buy formula

The buy formula is this manual's name for the arithmetic in the Food Buying Guide's first method, in household units:

1. Amount needed = people × portion per person × times served. "Times served" counts every meal the food is for, planned leftovers and packed lunches included.
2. Amount to buy = amount needed ÷ what one pound as purchased gives.
3. Round up, once for each question. For loose weight at a counter, round the unrounded pounds up to the next quarter pound. For packages, divide the unrounded pounds by the package size and round up to the next whole package. Divide the unrounded figure, not the rounded one.

The guide says to round up whenever you work out how much food to buy, and its worked examples do so, for example 195 servings ÷ 11.16 per pound = 17.47, so it buys 18 lb. Rounding down leaves a meal short; rounding up leaves a little extra to plan into the eat-down meal or freeze. The buy calculator does all three steps for the foods in the table above and shows its working.

Three worked figures, all from the calculator's arithmetic. The households are this manual's fictional cases; their plans are invented.

The ground beef needs 12 oz cooked and one pound gives 11.8, so a 1 lb pack is just short at the reference portion and the formula rounds to 1.25 lb. A household that eats a little less may find 1 lb enough; its own portions settle it, as they do for the Grants, whose four reference portions include four-year-old Leo's. Jordan's rice is already in the cupboard, so the figure answers a different question: does the kitchen have about ⅓ cup of dry rice? (The guide's 1 cup dry gives about 3¼ cups cooked.) Shopping and budget ticks it as "already have". Test it

Write each amount on the shopping list with the meals it is for. EPA's Smart Shopping sheet asks for the quantity or number of meals next to each fresh item, with the example "salad greens: lunch for a week". "Chicken thighs, 1.5 lb, for 5 meals" tells you at the store that a 2-lb pack is a choice to plan, not a bargain to grab.

Packages rarely match the figure. The calculator's package line shows how many packs cover it, counted from the unrounded pounds. Four people eating 3 oz of boneless chicken thighs at two meals need 2.38 lb, so the loose-weight amount reads 2.5 lb, but one 2.4 lb pack covers it; dividing the rounded 2.5 lb by 2.4 would have sent you home with two. Four people at the same two meals in 1.5 lb packs do need two. Plan what is left over as a named meal or a portion frozen the day it is bought or cooked (planned leftovers, freezing).

Iowa State's servings-per-pound rule

Iowa State's Spend Smart. Eat Smart. protein page gives a shorter rule for meat at the store: one pound serves four when it has no bones or fat (ground beef, stew meat, boneless ham, fish fillets), three when it has some bone and fat (pork chops, chuck roast, turkey parts), and two when it has many bones or more fat (whole chickens and turkeys, spare ribs) (Iowa State, Aisle by Aisle: Proteins). It is one extension service's rule of thumb. It cites no source and does not say what size a serving is.

Set beside the yield table, the rule fits some foods better than others. Ground beef up to 20% fat gives 11.8 oz cooked per pound; four servings is about 3 oz each, close to the reference portion. Boneless chicken thighs give about 10 oz; four servings is about 2½ oz each. That is our arithmetic. By Iowa State's rule Jordan's five uses need 1¼ lb; by the yield table and the reference portion, 1.5 lb. Use the rule as a quick check at the meat counter, and the buy calculator when the food is on its list.

4. Scaling a recipe, and what does not scale

Most recipes are written for four to eight servings. K-State Research and Extension's sheet on reducing recipes notes that recipes are usually 6 to 8 servings (K-State, Cooking Basics: Reducing a Recipe). A household of one or two halves or thirds most of them, and a large household doubles some.

The scaling factor is the number every ingredient amount is multiplied by. University of Wyoming Extension's newsletter on scaling gives the method: divide the servings you want by the servings the recipe makes, then multiply each ingredient by the result (Wyoming Extension, Scaling: Up or Down). Six servings from a ten-serving recipe is 6 ÷ 10 = 0.6. Two from four is 0.5. Eight from four is 2.

The product is often an awkward amount: half of ⅓ cup is not on any measuring cup. Nebraska Extension's page on reducing recipes gives tables in kitchen measures, using 1 cup = 16 Tbsp and 1 Tbsp = 3 tsp (Nebraska Extension, Reducing the Size of Recipes). Illinois Extension's and Colorado State's pages on cooking for one or two print the same halving figures (Illinois Extension, Cooking for One or Two; Colorado State, Healthy Eating for One or Two).

The recipe scaler works out the factor, multiplies up to eight ingredients, and shows each result in kitchen measures and in metric. Count items such as eggs and tortillas come out as numbers; part of an egg is the case covered below.

What does not scale in a straight line

Multiplying every amount by the factor works for the bulk of most savory recipes: the meat, vegetables, grains, liquid and sauce. Several things do not follow the factor:

• Seasoning. When halving, K-State says to use a little less than half of the herbs, spices and seasonings and add more if needed, and Wyoming says the same. When doubling, Wyoming suggests about 1½ times the original rather than twice. Start low and taste; salt and spice can be added and not taken out. Test it
• Fat for browning or sautéing. Wyoming says there is no need to double it. In our reading the pan's surface, not the batch, sets how much is needed, so when halving, use enough to film the smaller pan. Test it
• Pan size and food depth. Nebraska and K-State say to keep the food at the same depth when you change pans, and Wyoming uses a pan of double the volume, or two of the original pans, for a doubled recipe. Depth controls how heat reaches the middle (pans).
• Cooking time. A smaller amount at the same depth may cook faster, and a larger one slower. K-State starts by cutting the time in half for a halved recipe and checking, adding time as needed. When scaling up, Wyoming starts checking at the original time. Doneness is checked with a food thermometer against FSIS's safe minimum internal temperature chart, whatever the batch size (cooking temperatures). Test it
• Oven temperature. K-State keeps the recipe's temperature unless the pan changes to glass or dark metal, which it lowers by 25 °F (about 14 °C). Wyoming keeps it too, and adds time or raises it about 25 °F when several pans share the oven.
• Half an egg. A large egg is about ¼ cup, so half is 2 Tbsp: beat it and measure. K-State and Nebraska both give this figure. Refrigerate the rest covered and use it soon; Nebraska says within two to four days and K-State within two.
• Very large batches. Wyoming's limit is four times the recipe; past that, make separate batches.

5. Measures: US, metric and pans

US kitchen measures have exact legal definitions. NIST Handbook 44's tables define 1 cup as 8 fluid ounces exactly and 1 tablespoon as 3 teaspoons exactly, and the pound as 453.59237 grams exactly (NIST Handbook 44, Appendix C). One US fluid ounce is 29.5735 mL, so a cup is about 236.6 mL, which the handbook rounds to 237.

Two ounces share a name. The fluid ounce is a volume: 1/8 cup. The ounce of weight (the avoirdupois ounce) is 1/16 lb, about 28.35 g. They match only for water and liquids of about the same density. A cup of flour weighs far less than 8 oz and a cup of honey more. The unit converter converts volume to volume and weight to weight, and refuses volume to weight, because that needs the ingredient's density.

For cooking, NIST's Metric Kitchen pages use rounded kitchen approximations, marked as approximate (NIST, Cooking Measurement Equivalencies):

NIST's culinary measurement tips call weighing ingredients on a kitchen scale a best practice for recipe accuracy over measuring by volume, and name using a dry cup for liquid, or the reverse, as a common source of error (NIST, Culinary Measurement Tips). The same page warns that customary units mean different things in different countries, so a cup in an older recipe from elsewhere may not be a US cup. To tare a scale is to set it to zero with the bowl on it, so it reads only what you add. If a recipe gives grams, weigh; if it gives cups, measure with US cups; convert only when you must.

Pans: volume, area and depth

When a recipe changes size, the pan changes with it, and what has to stay the same is the depth of the food. Food depth is how thick the layer of food sits in the pan, and it sets how far heat has to travel to the middle. Pan volume is how much the pan holds to the rim. NIST's cookware page measures it by filling the pan with water on a tared scale (water is about 1 g per mL) and lists approximate volumes by inside size (NIST, Cookware and Tools). K-State says a 9 × 13 × 2 in pan holds 14 to 15 cups.

Why the 8 × 8 in pan works for half a 9 × 13 in recipe: the 9 × 13 in pan's floor is 117 sq in; half of that is 58.5 sq in, and the 8 × 8 in pan's floor is 64 sq in. Half the food spreads over a slightly larger floor, so it sits at about nine-tenths of its first depth. NIST's volumes say the same: half of 3.5 L is 1.75 L, in a 2 L pan. That is our arithmetic on the sources' figures. A slightly shallower layer can cook a little faster, which is one more reason to check early.

Doubling works in reverse: a pan of twice the volume, or two of the original pans. Without the right size, measure your pans with water and choose the one that keeps the depth closest.

6. See it: Jordan's chicken and the Delgados' casserole See it

Free sources behind this chapter:

• USDA Food Buying Guide, Introduction: how yields are measured, the six columns, and the purchase arithmetic with worked examples.
• Wyoming Extension, Scaling: Up or Down: the scaling factor and a short list of what does not scale.
• Nebraska Extension, Reducing the Size of Recipes: the halving and thirding tables and the pan swaps.
• NIST, Metric Kitchen: rounded metric equivalents for home cooking, with linked pages on measuring and pans.

7. Practice: two purchase amounts and one scaled recipe Practice

Minimum: purchase amounts for the main ingredients of two meals on your plan, written on the shopping list, and one recipe scaled to your household. Time: about 30 minutes. Materials: your plan from The weekly plan, one recipe you cook often, the buy calculator and recipe scaler, and a measuring cup.

1. Pick two meals whose main ingredient is fresh or bought for the week, such as meat, a vegetable or a grain. If one ingredient covers several meals, count them all.
2. Fill the buy calculator for the first: food, people eating, times served, and the portion blank for the reference portion or your own figure if you know it.
3. Read the result: amount needed, amount to buy, and, if you enter the package size you usually buy, how many packages and what is left over.
4. Repeat for the second. If the food is not on the calculator's list, work out people × portion × times served on paper and allow for trimming and cooking; for meat, Iowa State's servings-per-pound rule is a quick check.
5. Write both on the shopping list with the amount and "for N meals". Tick Already have if the kitchen covers it.
6. Scale one recipe. Enter the recipe's servings and yours, and up to eight ingredients. Copy the scaled amounts onto the recipe and note the pan, the seasoning start and the time to start checking.
7. After the meal, note on the plan whether the amount was short, right or left extra.

8. Your kitchen Your kitchen

9. Check your work Check your work

Criteria

• Does each purchase amount count every meal the food is for, planned leftovers and lunches included?
• Is the portion either the reference portion, labelled as a starting amount, or your own measured figure?
• Was the amount needed divided by the yield, not bought pound for pound?
• Was the result rounded up, to a quarter pound or a whole package?
• Does the shopping list show the amount and the number of meals for each?
• Does the scaled recipe use one factor, with the seasoning, pan, depth and time notes checked?
• If the recipe is a baked good, did you keep it whole or bake separate batches?

Worked example

Jordan (fictional example) counts all five uses of the chicken, uses the reference 3 oz labelled as such, divides by the thigh yield of 10.07 oz per pound and rounds 1.49 lb up to 1.5 lb. The list reads "Chicken thighs, 1.5 lb, for 5 meals (2-lb pack planned; extra frozen Monday)". The tacos are scaled by one factor, 0.5, with the chili powder started low. What is not yet checked is Jordan's real portion, which the week will show.

Common mistakes

• Buying a pound of raw meat for a pound of cooked: boneless thighs give about 10 oz.
• Counting only the first meal when the food is also for a planned leftover or lunches.
• Rounding down to the package on the shelf and coming up one meal short.
• Reading a reference portion as how much someone should eat.
• Halving a cake or a yeast bread. Make the whole recipe and freeze part.
• Halving a casserole into the same 9 × 13 in pan, so it spreads thin and overcooks.
• Treating fluid ounces and ounces of weight as the same, or turning cups of flour into ounces without its density.

What is still unresolved

This chapter cannot tell you how much your household eats; your own measured portions do, over a few weeks. It does not settle which package or store gives the lowest price for the amount; the unit prices in Shopping and budget do (unit price). Portions for anyone on a medical diet come from their doctor or dietitian.

10. Knowledge check and scenario

Checklist

• Two planned meals have purchase amounts on the shopping list, each with the number of meals it is for.
• I scaled one recipe to my household and noted the seasoning, pan and time.
• I can say which reference portion I used and that it is a starting amount.
• I measured one real portion and used it in the buy calculator. (Go deeper; optional)
• I measured a baking dish's volume with water on a scale. (Go deeper; optional)