Guidance for Industry: Guidelines for Determining Metric Equivalents of Household Measures
The purpose of these guidelines is to assist manufacturers in determining the metric equivalent declarations (e.g., gram (g) and milliliter (mL) measures) of the common household measures that are declared on food labels. When FDA performs nutrient analyses to determine the accuracy of nutrition labeling, assessment of compliance is based on these metric quantities.
The Nutrition Labeling and Education Act of 1990 added section 403(q) to the Federal Food, Drug, and Cosmetic Act (21 U.S.C. 343(q)). This section specifies, in part, that the serving size is "an amount customarily consumed ... expressed in a common household measure that is appropriate to the food," or "if the use of the food is not typically expressed in a serving size, the common household unit of measure that expresses the serving size of the food" should be used. For example, for a product such as pancake mix that is an ingredient of a food, if 1/4 cup of pancake mix is required to make the customarily consumed amount of pancakes, the serving size of this pancake mix would be expressed as 1/4 cup of mix.
Serving sizes are determined from the reference amounts established in 21 CFR 101.12(b) and the procedures described in 21 CFR 101.9(b)(2) and must be expressed in both common household measures and equivalent metric quantities (21 CFR 101.9(b)(7)). As stated in 21 CFR 101.9(b)(5) the term "common household measure" or "common household unit" means cup, tablespoon (tbsp), teaspoon (tsp), piece, slice, fraction (e.g., 1/4 pizza), ounce (oz), fluid ounce (fl oz), or other common household equipment used to package food products (e.g., jar, tray).
For specific details of the final rules that apply to serving sizes, refer to the following sections of the Code of Federal Regulations (CFR):
21 CFR 101.9(b) Nutrition labeling of food; definition of serving sizes
21 CFR 101.9(b)(6) Single-serving containers
21 CFR 101.9(b)(8) Number of servings per container
21 CFR 101.12(b) Reference amounts customarily consumed per eating occasion
- Representative samples of a food should be selected using standard sampling techniques from various lots (Ref. 21 CFR 101.9 (g)(2)). For mixtures (e.g., solids in solids, such as brownies with nuts; solids in liquids, such as soup with vegetables) the sample selected should contain a representative amount of the incorporated solids.
- Good quality laboratory equipment (e.g., graduated cylinders, balances, etc.) should be used to measure or weigh the food. Equipment should be calibrated in accordance with good laboratory practices and/or manufacturer's specifications.
- Standard analytical practices should be used for accurately determining product weights and volumes. Significant digits should be retained in order to minimize rounding errors in reporting final values.
- Each set of measurements should be determined by the same trained operator using the same methodology (i.e., the same equipment, procedures, and techniques) under the same conditions. For variable products (e.g., small pastas, snacks) another set of measurements should be determined by a second individual.
- All measurements should be replicated a sufficient number of times to ensure that the average of the measurements is representative of the product.
- Foods and containers should be at appropriate and compatible temperatures for volume determinations. Foods stored at room temperature should be measured at 20°C, refrigerated foods should be measured at 4°C, and frozen foods should be measured at the frozen temperature.
- The quality of the food product should be maintained throughout. Moisture gains or losses should be minimized. Fragile products should be handled carefully to minimize product breakdown. For example, flake breakfast cereals should be carefully transferred to volumetric containers and should not be sifted, stirred, or packed. Measurements should be made prior to excessive handling or shipping.
- The food volume measured should be at least 10 times the reference amount for the category in order to minimize measuring errors. (For example, dividing the weight of a cup of a product by 16 and 48 provides the tablespoon and teaspoon weights, respectively.)
- For purposes of nutrition labeling, 1 cup means 240 mL, 1 tablespoon means 15 mL, 1 teaspoon means 5 mL, 1 fluid ounce means 30 mL, and 1 ounce means 28 g (21 CFR 101.9(b)(5)(viii)).
As defined in 21 CFR 101.9(b)(5)(i), the household measures of cups, tablespoons, or teaspoons should be used whenever possible. Fluid ounces may be used for beverages. These measures should be expressed as follows:
Cups: 1/4, or 1/3-cup increments
Tablespoons: Whole numbers of tablespoons for quantities < 1/4 cup but ≥ 2 tbsp
1, 1 1/3, 1 1/2, 1 2/3 tbsp for quantities < 2 tbsp but ≥ 1
Teaspoons: Whole numbers of teaspoons for quantities < 1 tbsp but ≥ 1 tsp
1/4-tsp increments for quantities < 1 tsp
If cups, tablespoons, or teaspoons are not applicable, units such as piece, slice, tray, jar, and fractions should be used (21 CFR 101.9(b)(5)(ii)). The fractional slice of a food that most closely approximates the reference amount should be expressed as follows (21 CFR 101.9(b)(2)(ii):
Fractions: 1/2, 1/3, 1/4, 1/5, or 1/6, and smaller fractions that can be generated by further divisions by 2 or 3 (such as 1/8, 1/9, 1/10, 1/12, 1/15, 1/16, etc.).
If other units are not applicable, ounces may be used and must be accompanied by an appropriate visual unit of measure, for example, 1 oz (28 g/about 1 inch slice of cheese) (21 CFR 101.9(b)(5)(iii)).
- When the serving size is exactly half way between two values, it should be rounded to the higher value (21 CFR 101.9(b)(5)(ix)), for example, 2.5 tbsp is rounded to 3 tbsp.
Grams and milliliters should be rounded to the nearest whole number except for quantities that are less than 5 g or 5 mL. Gram and milliliter quantities between 2 and 5 should be rounded to the nearest 0.5 g or 0.5 mL. Gram and milliliter quantities less than 2 should be expressed in 0.1 g (or 0.1 mL) increments (21 CFR 101.9(b)(7)).
The provisions in 21 CFR 101.9(b)(7) exempt single-serving containers from listing metric equivalents except when nutrition information is on a drained weight basis in accordance with 21 CFR 101.9(h)(9). If companies voluntarily list metric equivalents for single-serving containers, the value must agree with the net quantity of contents expression.
FDA is unaware of any need to make changes in the procedures for determining metric equivalents of household measures due to the effects of variations in altitude. The agency will consider the need for altitude corrections should data become available.
Liquids may be measured in volumetric glassware or graduated cylinders. The level should be read at the lowest part of the meniscus and care should be taken to avoid parallax error. For clear liquids, a shade or dark material behind the meniscus may improve observation.
The volume being measured should be within 25 percent of the total capacity of the glassware selected. Select the smallest container that will hold the intended volume.
Techniques for determining the volumes of viscous liquids (e.g., syrups, molasses), fluid-type solids (e.g., applesauce, hot breakfast cereals), and spoonable thick or gelatinous solid-type liquids (e.g., gelatins, mayonnaise) include direct fill and volume displacement:
a. Direct fill - Direct fill involves carefully transferring the product to avoid incorporating air bubbles, allowing time for settling (viscous liquids are higher in the center when first poured), and, if necessary, leveling with a straight edge or by extrusion. For example, for a hot breakfast cereal product, a density cup of known weight and volume may be used to determine the volume to weight relationship: the cereal is transferred to the measuring container, the sliding disk is moved into position leaving a small gap, the excess cereal escapes through the opening and is wiped away, and the weight of the known volume of cereal can be determined by difference.
b. Volume displacement - Volume displacement involves adding a second material to fill the air space above the product. For example, a measured amount of water can be added to completely fill the air space above the mayonnaise in a mayonnaise jar. The volume of mayonnaise can be determined as the difference between the volume of the jar and the volume of water added. The material selected should not mix with the product being measured.
Fine particulate solids (for example, sugars, batter mixes, flours) may be leveled using a knife or other straight-edge after transfer to an appropriate volumetric measure (e.g., a cup measure would be appropriate for determination of tablespoons or teaspoons).
Medium particulate solids (i.e., nuts, flakes, pastas) should have the particle volume above the fill line approximately equal to the free air space found between particles immediately below the fill line.
For products where the packing liquid is not normally consumed (for example, olives, pickles, tuna fish, etc.), products should be drained for 2 minutes on a No. 8 sieve before weighing or measuring. AOAC procedures for canned vegetables and fish products are described in sections 968.30 and 937.07, respectively, of Official Methods of Analysis (Reference 1).
Products should be measured in the form in which they are packaged and sold (see 6 above). Some frozen products (e.g., frozen blocks of vegetables, frozen juice concentrates) cannot be transferred to volumetric containers in the frozen state. This type of product may need to be broken apart and/or defrosted slightly in order to fit into the measuring container. If necessary, cover and thaw the product minimally, transfer to measuring container, and return the product to its frozen state for measurement.
Techniques for determining the volumes of bulk solids (e.g., bulk cheeses) and irregularly-shaped solids (e.g., ice cream novelties) include direct measurement and volume displacement:
a. Direct measurement - Direct measurement involves creating a representative piece with regular dimensions. For example, the dimensions of a one ounce cube of cheese can be directly measured with a ruler.
b. Volume displacement - Volume displacement involves immersing the irregularly-shaped object in a known volume of another material and measuring the amount of material displaced. For example, an ice cream bar can be dipped briefly into a vat of cold liquid. The volume of the displaced liquid can be determined directly or by difference. The amount of displaced liquid is a measure of the volume of the irregularly-shaped ice cream bar.
Official Methods of Analysis, 15th Ed., AOAC, Arlington, VA (1990).