Length, Width and Height of a Box: How to Measure

The length, width and height of a box are its three outside measurements, written in that order: length is the longest side, width is the next-longest side, and height is the shortest side (usually the vertical one when the box sits flat). For shipping, measure the outside of the sealed box and round each side up to the next whole inch, because that is how UPS and USPS calculate size limits and dimensional weight.

Getting the order and the measurement right matters because carriers price large, light boxes by size as well as weight. A box listed as 12 × 10 × 8 when it is really 13 × 10 × 8 can bill at a higher weight or trigger a correction later.

Which Side Is the Length, Width and Height of a Box?

Carriers follow one convention: length first, then width, then height (L × W × H). Length is always the longest dimension, so a box measured 10 × 16 × 8 should be written 16 × 10 × 8.

Box makers sometimes list inside dimensions in a different order, such as length × width × depth, but shipping systems expect the longest side first. Our guide on how to read dimensions covers the notations you’ll see on product pages and box listings.

How Do You Measure the Length, Width and Height of a Box?

You need a rigid tape measure and a flat surface. Measure the box after it is packed and taped, because bulging sides add size.

1. Seal the box. Pack and tape it first, then set it on a flat floor or table.
2. Measure the longest side. Run the tape edge to edge along the longest side of the top. That is the length.
3. Measure the next side. Measure across the top at a right angle to the length. That is the width.
4. Measure the height. Measure from the floor to the highest point of the top, including any bulge.
5. Round up. Round each measurement up to the next whole inch: 11.1 inches becomes 12.
6. Write it down in order. Record it as L × W × H, longest side first.

Measure at the widest point of each side, not the middle, because a slightly crushed or overstuffed box isn’t perfectly square. Include anything that sticks out, such as handles or a strapped-on part.

Should You Use Inside or Outside Box Measurements?

Use outside measurements for shipping. Carriers apply their size limits and dimensional weight to the outside of the package, while inside measurements only tell you whether your item will fit.

Corrugated walls make the outside bigger than the inside. Single-wall board is roughly 1/8 to 3/16 inch thick and double-wall roughly 1/4 inch, so a box sold as 12 × 10 × 8 inside can measure about half an inch more on each side outside. When you order a box, check which set of numbers the supplier lists.

How Do Box Dimensions Turn Into Dimensional Weight?

Multiply the length, width and height to get cubic inches, then divide by the carrier’s divisor to get dimensional (DIM) weight. The carrier bills whichever is greater, the actual weight or the DIM weight.

Example: a 16 × 12 × 8 inch box is 1,536 cubic inches. At UPS, 1,536 ÷ 139 = 11.05, which rounds up to a 12-lb DIM weight, so a 4-lb item in that box bills as 12 lbs. USPS wouldn’t apply DIM pricing, because the box is under 1 cubic foot. Our guide to dimensional weight at UPS works through more examples.

What Size Limits Depend on Box Dimensions?

Box dimensions also decide whether a package triggers a size fee or goes over a carrier’s limit. These thresholds use the same rounded outside measurements.

Length plus girth is the longest side plus twice the width plus twice the height. For a 20 × 14 × 10 box, girth is 2 × (14 + 10) = 48, so length plus girth is 68 inches. Our girth calculator guide does the math for you.

For reference, a 24 × 24 × 18 box is exactly 10,368 cubic inches, so even one more inch on any side pushes it over the UPS Additional Handling volume threshold. Long items like bikes hit the length limits first; our page on typical bike box dimensions shows how bike boxes compare with these thresholds.

What Are Common Box Measuring Mistakes?

Most measuring mistakes make the label smaller than the real box, which can lead to a billing adjustment after the carrier re-measures it.

• Using the inside dimensions from the box listing instead of measuring the outside.
• Measuring before packing, then overfilling the box so it bulges.
• Rounding down a fraction of an inch instead of up.
• Listing sides in the wrong order, which can hide a length that crosses a size threshold.
• Leaving out protrusions such as handles, wheels or items strapped to the box.
• Measuring at the middle of a side instead of its widest point.

How Do You Measure a Box That Isn’t Square?

Measure the longest, widest and tallest points as if the item were inside the smallest rectangular box that would hold it. For a tube or cylinder, use the length along the tube, and use the diameter for both the width and the height.

For soft packages like poly mailers, lay the package flat and measure its length, width and thickness at the fullest point. Whether a padded mailer is billed as a package or an envelope also depends on its thickness; our guide on whether bubble mailers are considered packages explains the USPS rules.

How Can You Ship a Box for Less Once You Know Its Size?

Choose the smallest box that holds the item with about 2 inches of padding. Trimming even one inch off each side can reduce DIM weight or keep a box under a size threshold.

Then compare carriers, because UPS and USPS apply DIM weight differently: USPS skips it for boxes of 1 cubic foot or less. Enter your measured length, width, height and weight in the ParcelPath rate calculator to see live UPS and USPS prices side by side. ParcelPath is free, with up to 85% off UPS and up to 89% off USPS retail prices, and for palletized shipments that outgrow parcel limits, PalletPath quotes LTL freight through the freight quote tool.

Frequently Asked Questions

What order do you write the length, width and height of a box?

Write box dimensions as length × width × height, with the longest side first. Length is the longest side, width is the second-longest side at a right angle to it, and height is the shortest, usually vertical, side. A box measured at 10, 16 and 8 inches should be listed as 16 × 10 × 8 on a shipping label or rate quote.

Do you round box measurements up or down for shipping?

Round each measurement up to the next whole inch. UPS rounds every side up before calculating dimensional weight, and USPS rounds partial inches up as well. A side that measures 11.1 inches counts as 12 inches, so measuring precisely and choosing a box that fits snugly can keep the billed size down.

Is height the same as depth on a box?

Usually, yes. Box sellers often write length × width × depth, where depth means the distance from the opening to the bottom, which is the height when the box sits flaps-up. For shipping, it doesn’t matter what you call each side: list the longest side first and give all three outside measurements.

How do you calculate the cubic inches of a box?

Multiply the length, width and height in inches. A 16 × 12 × 8 inch box is 1,536 cubic inches. Divide by 1,728 to convert to cubic feet, which gives 0.89 cubic feet here. USPS applies dimensional weight only to packages over 1 cubic foot, while UPS applies it to every package.

Sources

• USPS Ground Advantage: dimensional weight, nonstandard fees and size limits
• USPS Domestic Mail Manual 101: Physical Standards (length plus girth limits)
• UPS rate and service guide: dimensional weight, Additional Handling and Large Package criteria (ups.com)

Browse more packaging guides in Shipping Resources.

Part of our Packaging guide. Related: Shipping Resources, Are Bubble Mailers Considered Packages?.