U. S. Food and Drug Administration
Center for Food Safety and Applied Nutrition
Office of Food Labeling
October, 1993
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 |
General Information
- 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.
Liquid Measurements
- 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:
Solid Measurements
- 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:
References
- Official Methods of Analysis, 15th Ed., AOAC, Arlington, VA
(1990).
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