No matter which shipping service you choose, the cost of shipping will depend on the length, width, and height of your package. As such, it is crucial that you know the dimensions of the box you plan to ship.
StepsEdit
Method One of Three:
Measuring Length and Girth for Regular (Rectangular) PackagesEdit

1Measure the longest side of the package. Determine which side of the box is longest, then measure the full length of this side from one end to the other using a measuring stick.
 Round this measurement off to the nearest inch (2.5 cm).
 This measurement is the length of your package.

2Measure the width of the package. The width of your box is the shorter side of the bottom or top face (or the open side) of the box. Measure the full distance of this side from one end to the other using a measuring stick.
 Round this measurement off to the nearest inch (2.5 cm), as well.
 Even if you mix up the height and width measurements, the final calculation should not be thrown off. The only side you absolutely must identify accurately is the length.

3Measure the height of the package. Use a measuring stick to measure the standing side of the box from one end to the other. This is your height measurement.
 The height should be the only side previously unmeasured at this point.
 Round the measurement to the nearest inch (2.5 cm).

4Double the width and height measurements. Multiply the width by two. Multiply the height by two, as well.
 Neither of these calculations have a separate term, but you'll need to know them for your final girth calculation.
 Do not double the length measurement.
 For example, if you have a box with a length of 12 inches (30.5 cm), a width of 4 inches (10 cm), and a height of 6 inches (15.25 cm), you would only need to double the width and height:
 Doubled width: 4 * 2 = 8 inches (20 cm)
 Doubled height: 6 * 12 = 12 inches (30.5 cm)

5Add the doubled measurements together. Add the doubled height and doubled width measurements together. The combined sum equals the girth of the box.
 The girth is essentially the total distance around the thickest part of the box.^{[1]}
 In the previous example, the doubled width was 8 inches (20 cm) and the doubled height was 12 inches (30.5 cm). As such, the girth would be found by adding these two calculated measurements together:
 Girth: 8 + 12 = 20 inches (50.5 cm)

6Calculate the combined length and girth. When shipping ground packages, you may need to know the overall size of the package. This can be found by adding the length and girth measurements together.
 In the previous example, the girth of the package was 20 inches (50.5 cm) and the length was 12 inches (30.5 cm). To find the overall package size, you need to add these two measurements together:
 Size: 20 + 12 = 32 inches (80.5 cm).
 In the previous example, the girth of the package was 20 inches (50.5 cm) and the length was 12 inches (30.5 cm). To find the overall package size, you need to add these two measurements together:

7Note the final measurements. You should have all the necessary measurements needed to ship your box at this point. Keep a note of each separate measurement so that you'll be able to provide the shipping service with the exact information required.
 You might be asked for:
 Separate length, width, and height measurements (L; W; H)
 Length and girth measurements (L; 2W + 2H)
 Total package size (L + 2W + 2H)
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Method Two of Three:
Measuring Irregular PackagesEdit

1Measure the longest side of the package. Determine which side of the package is longest. This will be used as the length measurement.
 Measure the longest distance from one end to the other using a measuring stick. Only measure along the outer edge if the outer edge is the longest point. If the longest distance lies somewhere in between the outer edges of the package, you must measure there instead.
 Round the measurement to the nearest 1 inch (2.5 cm).

2Measure the widest part of the package width. Set the package down so that the length runs parallel to the table or floor. The other (shorter) parallel side is the width.
 Identify the longest distance along this width. It might be at one of the outer edges of the package, but it may lie somewhere in between the outer edges.
 Measure this widest portion of the package width using a measuring stick. Round this measurement to the nearest 1 inch (2.5 cm).

3Measure the deepest part of the package height. Identify the remaining unmeasured side. It should run perpendicular to the floor or table. This side is the height of the package.
 Look for the tallest point of the package. Measure from this point down to floor or table, where the bottom of the package rests. Do not measure along the outer edge of the height unless that outer edge is the tallest one.
 Use a measuring stick and round off your measurement to the nearest 1 inch (2.5 cm).

4Treat the package as a rectangular box. To calculate the girth or overall size of the box, apply the same method you would use when calculating the measurements of a regular rectangular box.^{[2]}
 When asked for separate length, width, and height measurements, provide the measurements you just took as they are.
 When asked for length and girth measurements, provide the length measurement you just took as it is. For the girth, double both the width and height measurements, then add the two doubled values together.
 Example: Length = 6 inches (15 cm); Width = 2 inches (5 cm); Height = 4 inches (10 cm)
 Girth = (2 * 2 inches [5 cm]) + (2 * 4 inches [10 cm]) = 4 inches (10 cm) + 8 inches (20 cm) = 12 inches (30 cm)
 When asked for the total package measurement, add the girth and length together.
 Example: Girth = 12 inches (30 cm); Length = 6 inches (15 cm)
 Total size = 12 inches (30 cm) + 6 inches (15 cm) = 18 inches (45 cm)
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Method Three of Three:
Measuring Dimensional WeightEdit

1Measure the length, width, and height. Use a measuring stick to measure all three sides of the package. Round these measurements to the nearest 1 inch.
 When measuring dimensional weight, it doesn't matter which side you label as the length, which you label as the width, and which you label as the height. You only need to make sure that all three sides are properly measured.
 For each side, use a measuring stick to measure from one edge to the opposite edge. Write each measurement down separately and round each one to the nearest 1 inch.
 Note that these dimensional weight calculations can only be used with imperial units of measurement. The calculations will not work for metric measurements. (To use the formulas below with the metric system, replace 166 with 5000.)

2Calculate the volume. Calculate the volume of the package by multiplying the length, width, and height together.
 For example, if you want to ship a package with a length of 12 inches, width of 8 inches, and height of 4 inches, you would calculate the volume by multiplying all three measurements together:
 Volume = 12 inches * 8 inches * 4 inches = 384 cubic inches
 For example, if you want to ship a package with a length of 12 inches, width of 8 inches, and height of 4 inches, you would calculate the volume by multiplying all three measurements together:

3Divide the volume by 166. For shipments within the United States or Puerto Rico, divide the volume of the package by 166. For international shipments, divide the volume by 139.^{[3]}
 For a package with a volume of 384 cubic inches
 Domestic dimensional weight = 384 cubic inches / 166 = 2.31
 International dimensional weight = 384 cubic inches / 139 = 2.76
 For a package with a volume of 384 cubic inches

4Take the actual weight. Use a postal scale to measure the true weight of the package in pounds.
 If you do not own a postal scale, you will need to have the weight of the package measured at the shipping office.

5Compare the dimensional weight to the actual weight. If the dimensional weight is greater than the actual weight, the shipping service may need to charge a greater amount than the base fee indicated for your package dimensions.
 Dimensional weight is only an estimate, not a precise measurement.
 When a package is light or moderately heavy based on its volume, the price of shipping will usually be based on dimensional weight, length, width, and volume. Abnormally heavy packages will need to be priced based on actual weight.
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Community Q&A
TipsEdit
Things You'll NeedEdit
 Measuring stick (ruler, yardstick, meter stick)
 Postal scale (optional)