Find the right box
for your item, by billed weight

Enter what you’re shipping. Get the standard box sizes it fits, ranked by the weight FedEx, UPS, USPS or DHL would bill — and whether a slightly different box would bill less.

Rules verified 22 Sep 2026Carrier figures use the carriers’ own published rules: USPS DMM 223 (Priority Mail: DIM weight, cubic, nonstandard fees) · USPS DMM 133 (Ground Advantage — Retail) · USPS DMM 283 (Ground Advantage — Commercial, cubic) · USPS DMM 101 (maximum size and weight) · UPS 2026 Rate and Service Guide (Daily Rates) · UPS 2026 Rate and Service Guide (Retail Rates) · FedEx Service Guide 2026 · DHL Express US Service & Rate Guide 2026 · Amazon Seller Central — Product size tiers · USPS — Priority Mail (Flat Rate box sizes). Carriers change these rules, usually each January and July — confirm against your own rate sheet or account.
Item size
Box wall thickness

Box sizes are listed as inside dimensions; carriers measure the outside. If your supplier gives a wall thickness, enter it and the billed weights use the outside size.

How it works

Smallest box isn’t always cheapest to ship

The finder adds your padding to the item on every side, then checks each of our 155 standard box sizes in every orientation. For each box that fits, it works out what the carrier would bill: the greater of the actual weight and the dimensional weight (outside L × W × H ÷ 139 for FedEx, UPS Daily Rates and DHL, ÷ 166 for UPS Retail, rounded up to the next lb), plus the 40 lb minimum for Additional Handling or 90 lb for Large Package / Oversize when a box crosses those lines. USPS only charges dimensional weight over 1 cubic foot (1,728 in³), so a slightly larger box under that line can bill less at USPS than a snug one over it.

Boxes are ranked by billed weight, then by size. The custom-box line shows what a box cut exactly to your item (rounded up to whole inches) would bill, so you can see what the nearest standard size costs you. It also tells you if the item fits a USPS Flat Rate box, which is priced per box instead.

Billed weight is not a price: rates also depend on zone, service and your account. Weight-based surcharges (for example UPS and FedEx Additional Handling over 50 lb) aren’t shown. If you want to check what a carrier actually billed, the figures are printed on the label — see how to read a FedEx shipping label.

FAQ

Questions

How do I choose the right box size for shipping?
Measure the item, add the padding you need on every side, and pick the smallest box whose inside dimensions are at least that big in some orientation. Then check the billed weight: carriers charge the greater of actual weight and dimensional weight (L × W × H ÷ 139 at FedEx and UPS Daily Rates), so a box one inch smaller on its biggest side can save several pounds.
How much padding should I leave around an item?
It depends on how fragile the item is and what you pack it with — check your carrier’s packaging guidelines. The finder lets you set any padding; the chips offer 0.5, 1 and 2 inches as starting points.
Why does the finder sometimes pick a bigger box?
Because it can bill less. USPS doesn’t charge dimensional weight on parcels of 1 cubic foot (1,728 in³) or less, and UPS and FedEx add a 40 lb minimum billable weight once a box is longer than 48 in, has a second side over 30 in, is over 105 in length + girth or over 10,368 in³. A box that stays under those lines can beat a tighter one that doesn’t.
Are the box sizes inside or outside dimensions?
Inside. Carriers measure the outside, which is larger by the wall thickness on each side. Open “Box wall thickness” and enter your supplier’s figure to bill on the outside size. The home calculator has the same control, and for a rigid plywood or MDF box there is a dedicated speaker box volume calculator.