box size & shipping cost calculator for eBay, Etsy, Poshmark & Depop sellers
Enter your item's dimensions and we'll match it to the smallest box, bubble mailer, or envelope that actually fits, from everyday store-bought boxes to USPS, UPS, and FedEx packaging. Then estimate what it'll cost to ship by ZIP code.
selling platform
carrier
ship it in
cushioning allowance on each side
Estimated retail rates. Your actual label cost may be lower through eBay, Etsy or Poshmark.
Measure your item, then add about 1 inch of padding on every side. A 10" x 6" x 4" item needs a box at least 12" x 8" x 6" inside. Go as small as you safely can, since bigger boxes can cost more to ship. Enter your measurements above and BoxSizeFit picks the smallest standard box that fits.
Carriers charge by size as well as weight. This is called dimensional weight. If a box is over 1 cubic foot (1,728 cubic inches), USPS works out a "size weight" by multiplying length x width x height and dividing by 139, then charges whichever is higher, the real weight or the size weight. A big box with a light item inside can be billed like a heavy one, so a snug box saves money.
Use a tape measure and measure the longest side first. That's the length. The next longest side is the width, and the shortest is the height. Round up to the next quarter inch. If you're measuring a box, measure the outside, because that's what the carrier measures.
For most packages under a few pounds, USPS Ground Advantage is cheaper and takes 2 to 5 business days. Priority Mail is faster, 1 to 3 business days, and sometimes costs about the same for heavier boxes going far. Flat Rate boxes can win for heavy items going across the country. The calculator above shows all of them side by side.
No. USPS's free Priority Mail boxes and envelopes can only be used for Priority Mail or Priority Mail Express. For Ground Advantage, use a plain box, a reused box, or a mailer.
Poshmark's prepaid label covers USPS Ground Advantage packages up to 5 lb. If your packed item is heavier, you can get an upgraded label for packages up to 15 lb, and that extra cost is charged to you. Weigh the box with everything inside before you ship.
Yes, as long as the box is sturdy with no tears or crushed corners. Remove or completely cover the old shipping labels, barcodes, and any hazardous material markings so the carrier doesn't scan the wrong one.
BoxSizeFit includes common long boxes, and if nothing standard fits, it sizes a custom box to your item and still estimates shipping. USPS adds an extra fee for packages longer than 22 inches and a bigger one over 30 inches, and that's included in the estimate.
They're estimates based on USPS's published retail prices and an estimated distance zone. What you actually pay is often lower when you buy the label through eBay, Etsy, or Poshmark, so use these numbers to compare options and set shipping charges.
Yes. It's free to use, with no account or sign-up needed.