Practice food-label weight units with a kitchen scale.

Match the weight unit.

Most US Nutrition Facts labels give the serving size twice. The FDA explains that it appears first as a common household measure, such as a cup, a piece or a slice, followed by the metric amount in grams (g). Weight can also appear in ounces, for example in the net weight (“Net Wt”) printed on the package.

NIST points out that the fluid ounce (fl oz) and the ounce of weight (oz) are different units with similar names.

To change ounces into grams, NIST’s conversion table gives the factor: 1 ounce = 28.35 grams. For example, a fictional package marked “Net Wt 16 oz” works out to 16 × 28.35 = 453.6 g, or about 454 g once rounded. Set your scale to the same unit as the number you are checking, so you do not have to convert at all.

Tare the empty bowl.

The tare (or “zero”) button removes the weight of the bowl from the display. NIST describes pressing zero before each new measurement so the scale shows only what you add next. Read your scale’s manual first, check its capacity limit, and place it on a firm, level surface.

A good first practice item is a sealed package you already have. Weigh it unopened, then compare the reading with the net weight printed on it. Your reading will usually be a little higher, because the scale also weighs the packaging. That difference is a useful lesson: always ask what exactly is on the scale.

Try a fictional label exercise.

Write your answer in a full sentence: “The bowl holds about 2 of the label’s servings.” That sentence describes the label. It does not say whether 2 servings, or any amount, is right for anyone.

Try one variation. If the label had said 1 oz instead of 30 g, you would first convert: 1 oz = 28.35 g. Then 60 g ÷ 28.35 g is a little more than 2. Small differences like this are why matching units matters before you compare.

Keep the result in context.

This exercise has clear limits. Keep them in mind so the numbers do not say more than they can:

• Food weight is not nutrient weight. A 30 g serving does not contain 30 g of any single nutrient.
• Preparation changes weight. Cooking, draining or soaking can change how much a food weighs, so a dry weight and a cooked weight are not comparable.
• Home scales vary. Small scales round their readings, and accuracy depends on the scale and its batteries.
• A serving size is not advice. The FDA says the serving size on a label reflects what people typically eat and is not a recommendation of how much to eat.

Practice without buying a scale.

You do not need a scale to learn the units. Copy the serving information from any label at home, circle the unit, and write whether it is weight or volume. Then do the arithmetic on paper with the label’s own numbers. Exercise 3 in the free workbook walks through the same idea, and our article on food-label units covers weight and volume side by side.

If you do decide a scale would help, our guide to kitchen scales for food-label practice lists what to check: units, display, tare and capacity. It names no products, and a scale you already own may be enough.