Weighing Food for Calorie and Macro Tracking

Tracking what you eat only works if the amounts you enter are close to the amounts you eat. This guide explains how to weigh food on a kitchen scale, how to turn grams into calories and macronutrients, how much slack the numbers on a label have, and why raw and cooked weights are not interchangeable. It is general information for adults, not dietary advice. For choosing a scale, see our buying guide, which also lists the cautions to read first.

Why weigh at all

NIDDK points out that a serving is the amount on the label and a portion is what you choose to eat, so the two can differ. FDA says the same from the label side: serving sizes reflect the amount people typically eat or drink and are not a recommendation. If your bowl holds two servings, the calories double.

Estimating by eye is harder than it feels. In a 2016 study in the Journal of Nutritional Science, 67 adults estimated the size of 42 pre-weighed foods and drinks. Of the geometrically shaped items they estimated with household measures such as cups and spoons, 29% were within 25% of the true weight and 8% within 10%. A 2025 paper in Nature Food applied an energy-expenditure equation to two national datasets, the UK's National Diet and Nutrition Survey and the US NHANES, and concluded that misreporting of intake in them was common. That is a finding about survey records, not about any one person, but it shows how hard amounts are to judge without measuring.

The basic method

1. Put the empty bowl or plate on the scale, switch it on and wait for zero.
2. Add the first food and note the grams. Press tare again before the next food, so each reading is one ingredient.
3. Record grams, not cups or "a bowlful", in your app or notebook straight away.
4. Weigh food in the state the entry describes (see the raw-and-cooked section below), and weigh the oil or butter you add.

A search for digital kitchen scales with a tare function on Amazon (opens in a new tab) shows models that have this feature.

From grams to calories

USDA's FoodData Central lists nutrient values per 100 g, and its FAQ calls these 100-unit measures. A label gives values per serving, with the serving's grams in parentheses. Either way the sum is simple: multiply the value per 100 g by your grams and divide by 100, or divide the label's calories by the serving's grams to get calories per gram. FoodData Central lists smooth peanut butter with salt at 598 kcal per 100 g, so 32 g, the 2 tablespoons it gives as a serving, is about 191 kcal. Our portion size calculator does the sums for calories, protein, carbohydrate and fat.

Under 21 CFR 101.9(c)(1), a label's calories may be worked out with the general factors of 4, 4 and 9 calories per gram of protein, total carbohydrate and total fat, or with more specific Atwater factors. A tracking app that mixes label data with its own database entries may therefore not add up exactly.

How much slack a label has

Label numbers are rounded and allowed some tolerance, so even a carefully weighed total is an estimate:

• Rounding. Calories are declared to the nearest 5 up to 50 and to the nearest 10 above 50, so a serving that works out to 163 prints as 160. Fat is declared to the nearest 0.5 g below 5 g.
• Tolerance. FDA treats a food as misbranded if its calories, total sugars, total fat, saturated fat, trans fat, cholesterol or sodium are more than 20% above the declared value. For naturally occurring protein, carbohydrate and fiber the floor is 80% of the declared value. FDA adds that it will not act on differences smaller than the variability of the analytical method.
• Grams decide. Compliance is judged on the metric amount in the serving-size statement, so a label that says 1 cup (125 g) is held to the 125 g.

Raw or cooked: pick the matching entry

A Nutrition Facts label describes the food as packaged or purchased, and a second column for the food as prepared is optional when directions are given. A bag of dry pasta therefore shows dry values. FoodData Central's SR Legacy data show how far raw and cooked entries differ per 100 g:

• Pasta. 371 kcal dry and 158 kcal cooked without salt. On those figures the cooked weight is roughly 2.3 times the dry weight, and 56 g of dry pasta, the 2 ounces that FDA's reference-amount rule shows for dry bulk pasta such as spaghetti, comes to about 208 kcal either way.
• White long-grain rice. 365 kcal raw and 130 kcal cooked.
• Lentils. 352 kcal dry and 116 kcal boiled.
• Chicken breast, skinless and boneless. 120 kcal and 22.5 g protein raw; 165 kcal and 31.0 g protein roasted. Cooked meat is more concentrated because it loses water, the opposite direction to pasta and rice.

Logging 100 g of cooked rice against the raw entry counts 365 kcal instead of 130, and logging cooked chicken against the raw entry undercounts its calories by about 27%. Whichever you weigh, log the matching entry, and weigh before cooking where you can.

Batches, sauces and recipes

For a pot of chili, add up the calories of the raw ingredients you weighed, weigh the empty pot, then weigh the finished dish in the pot and subtract. Your share is your portion divided by the dish's weight, times its total calories. If the ingredients came to 1,800 kcal and the finished dish weighs 2,400 g, a 300 g bowl is one eighth of it, or 225 kcal.

Oils, butter and sugar

FoodData Central lists olive oil at 884 kcal per 100 g and butter at 717 kcal, and gives a tablespoon of each as 13.5 g and 14.2 g. That is about 119 kcal of oil or 102 kcal of butter per tablespoon. Granulated sugar is 387 kcal per 100 g, about 16 kcal for a 4.2 g teaspoon. Weighing the oil into the pan takes seconds. For a few grams of a strong ingredient, kitchen scales that read to 0.1 g on Amazon (opens in a new tab) help, and our accuracy guide explains when 1 g is enough.

Keep it clean

FDA's food-safety advice is to wash hands with warm water and soap for at least 20 seconds before and after handling food, to keep raw meat, poultry, seafood and eggs apart from other foods, and never to put cooked food on a plate that held them unless the plate has been washed in hot, soapy water. Applied to a scale, weigh raw meat on a plate or in a container rather than directly on the platform, then wash the dish and wipe the scale.

How exact do you need to be

A scale with 1 g steps, such as those in this search on Amazon (opens in a new tab), is enough for most food. NIDDK says you may only need to measure long enough to learn typical serving and portion sizes. That can mean weighing for a few weeks and then checking now and then, since portions drift.

Cautions

NIDDK calls talking with a health care professional about your weight an important first step, and says they may review medical problems and the medicines or dietary supplements you take. NIMH notes that some people become fixated or obsessed with weight loss, body weight or shape, and controlling their food intake, and that these may be signs of an eating disorder. If weighing makes eating stressful, stop and talk to a health care provider. ANAD's free helpline is (888) 375-7767, weekdays 9 a.m. to 9 p.m. Central time, as ANAD's page puts it, and NIMH points to the 988 Suicide & Crisis Lifeline in a crisis. The CDC tells pregnant women to work with their health care provider on weight gain goals at the start of pregnancy and regularly after.

For when a measuring cup or spoon is enough, see scale or measuring cups and spoons. The label on the pack is the authority on that food, and your doctor or a registered dietitian is the right person to ask about your own diet.