Kitchen calculators: how much to buy, scaling, units, unit prices and keep times

Five small calculators for the numbers the chapters ask for: how much to buy from people and portions, a recipe scaled to your household, kitchen unit conversions, unit prices compared, and the day a food should be eaten or frozen by. Pre-filled from your setup.

Each calculator does arithmetic on published figures and says which ones. None of them knows your food, your appetite or your store: write each result on the sheet it belongs to and replace it with your own measured figure when you have one.

How much to buy

People × portion × times served gives the amount you need in its cooked or ready-to-eat form. Dividing by the food's yield turns that into the amount to buy as purchased, because raw weight is not cooked weight: a pound of dry rice becomes about 7 1/2 cups cooked, and a pound of boneless chicken thighs about 10 ounces cooked.

Assumptions

• Amount to buy = amount needed ÷ the portion units one pound gives as purchased, always rounded up. This is Method 1 of the USDA Food Buying Guide's introduction, which says to round up when working out how much to buy. We make two roundings, each from the unrounded figure: loose weight goes up to the next quarter pound, and packages are the unrounded pounds divided by the package size, rounded up to a whole package.
• The per-pound figures come from the Guide's yield tables for meats and beans, vegetables, fruits and grains: the quarter-cup servings per pound divided by four, or the cooked lean ounces per pound for meat. They are averages from school food service, where food is trimmed and portioned with care. The Guide lists the food's quality, storage, equipment, cooking method and serving utensils among the things that change a yield. Test it
• The reference portions are the serving examples in the Dietary Guidelines for Americans, 2025-2030 daily servings sheet: 3 oz cooked meat, poultry or seafood; 1/2 cup beans; 1/2 cup cooked grain; 1 cup vegetables; 2 cups leafy greens; 1 cup fruit. They are starting amounts for a shopping estimate, not intake targets; appetite differs by person and by day (How much to buy).
• The list holds the 18 foods whose yields were recorded from the Guide's public tables. For any other food, the Guide's own tables or your own weighing settle the yield.

Recipe scaler

Scaling factor = servings wanted ÷ servings in the recipe; every ingredient is multiplied by it. Amounts accept fractions (1 1/2, 3/4). Volume results are shown in the cups and spoons a kitchen has; weights stay in their unit with the other system beside them.

Assumptions

• The factor and the multiplication come from Wyoming Extension's Scaling: Up or Down. Its notes on seasoning, sauté fat, pan size, cooking time and the limit of four times appear under the result.
• Kitchen measures are rounded to the nearest 1/8 teaspoon, then written as cups (to 1/4 and 1/3 cup), tablespoons and teaspoons. A whole number of tablespoons under 8 stays in tablespoons, so 3/4 cup halved reads 6 Tbsp, as in Nebraska Extension's halving and thirding tables. The tables round a few awkward amounts differently from the calculator.
• Halving notes come from K-State's Reducing a Recipe (MF3531) and Nebraska's page. Neither gives a figure for leavening, so the scaler gives none. Test it

Unit converter

Assumptions

• Exact factors from NIST Handbook 44 (2026), Appendix C: 1 cup = 8 fluid ounces; 1 tablespoon = 3 teaspoons; 1 fluid ounce = 29.5735 mL; 1 pound = 453.59237 g.
• The rounded figures marked "about" are NIST's Metric Kitchen equivalencies (1 cup about 240 mL; 1 oz about 28 g), which match the markings on most kitchen tools.
• A fluid ounce measures volume and an ounce measures weight. The converter never turns one into the other: that needs the ingredient's density, which differs for flour, sugar and oil. Water is about 1 g per mL.

Unit price comparer

Unit price = price ÷ quantity, in one unit of measure for every item compared. Fill in two or three items as they appear on the shelf tag or the package.

Assumptions

• The definition and the units come from NIST's Unit Pricing Guide (SP 1181, 2025): weight per ounce, pound or 100 g; volume per fluid ounce, quart or liter; count per item. It says servings, loads and uses are not units of measure.
• Unit pricing on shelf tags is voluntary in the US unless a state requires it; NIST counts 16 states plus DC, Puerto Rico and the Virgin Islands with rules as of 2025. A store's tag may use a different unit for two items in one aisle; this calculator puts them on the same footing.
• Cost per serving = price ÷ the servings printed on the label, as Iowa State's Spend Smart unit pricing page shows it. It is only as good as the label's serving size, which is what people typically eat, not a recommendation.

Keep until: eat-by and freeze-by days

Turns a federal storage time into weekdays. The refrigerator time is a safety limit; the freezer time is a quality limit.

Assumptions

• Refrigerator times from FSIS's Refrigeration and Food Safety chart, its leftovers page and its shelf-stable food page (opened cans; rice and pasta after cooking). FSIS calls the chart's times short but safe limits.
• Freezer times from FSIS's Freezing and Food Safety chart and FoodSafety.gov's cold food storage chart. Both say freezer times are for quality only and that food kept constantly at 0 °F (-18 °C) stays safe.
• Counting the day of cooking, buying or opening as day 0 is our convention for turning "3 to 4 days" into weekdays; the federal pages give the times in days. A leftover turned into a new dish keeps its first cooking day (Leftovers and using it up).
• The times assume the food went into a refrigerator at 40 °F (4 °C) or below within 2 hours, or 1 hour above 90 °F (32 °C). They are not a promise about any one item, and food is never tasted to test it (How long food keeps). The full table is on the storage times page.