Mailer Box Sizes: Common Dimensions and How to Choose

A mailer box size is written as internal length x width x height in inches, and you choose it by measuring your product as it will actually be packed, then adding 1/8 to 1/4 inch in total to each dimension. For most ecommerce orders the starting point is 10 x 8 x 4.

Reviewed by the TBPB packaging team, October 2026.

What are the common mailer box sizes?

Most shops end up in a small cluster of sizes. The chart below lists internal dimensions in inches, with the approximate outside size assuming the walls add about a quarter inch to each dimension. Treat the outside column as a guide only, because it shifts with board thickness.

None of these is an official standard. They are just the sizes that keep coming up because folded clothing, a candle, or a three-item kit tends to land near them. If your product sits between two rows, do not round up out of habit. Go to the next section and size to the product.

Do mailer box dimensions mean inside or outside?

Inside. The internal number is the one that decides if your product fits, so that is the number to order by and the number to look for on any chart or quote. The outside is larger by the thickness of the walls, plus a little for the folds and glue seams.

The rule we use, stated plainly: order by internal size, and add your clearance to the product measurement once, per dimension. Clearance of 1/8 inch means 1/8 inch added to the length in total, so about 1/16 inch of play on each end. It does not mean 1/8 inch on each side. This is the point that trips people up, because a chart that says "add a quarter inch" can be read either way. Our figures are always totals.

The outside size still matters for two jobs: checking that boxes fit your shipping carton or mailbox slot, and reading carrier rules for size-based pricing. Carriers publish those rules on their own sites and change them, so check the live figures instead of trusting a number in an article. Ask us for the exact outside size on your dieline.

How do I work out the right size, step by step?

1. Pack one real order the way a customer will receive it: product folded or bagged, tissue, card, any insert.
2. Measure that packed stack at its longest, widest and thickest points with a ruler, in inches. Press it down lightly. Do not measure a loose, fluffy fold.
3. Add 1/8 inch to length and width for a snug fit, or 1/4 inch if you pack by hand and want it to slide in easily.
4. Add 1/4 inch to the height so the lid closes flat without bowing upward.
5. Round to the nearest 1/8 inch and order that internal size.
6. Order a single box, pack a real order, close the lid, and shake it. Adjust, then reorder in volume.

What does a worked example look like?

Take a folded cotton tee wrapped in one sheet of tissue, with a thank-you card on top. Packed and lightly pressed, it measures 9.5 x 7.5 inches across and 1.75 inches thick, and the card adds 0.25 inch to the height, so the stack is 9.5 x 7.5 x 2.

So the order is 9.75 x 7.75 x 2.25 inside, and with typical walls the outside lands near 10 x 8 x 2.5. Now compare that with grabbing the popular 10 x 8 x 4. It fits, but it is 1.75 inches too deep, so the tee rattles around in nearly twice the empty volume it needs, you pay for extra board and void fill, and the package sits bulkier in the carrier network. The custom size costs you a few minutes of measuring and saves money on every order.

Why does depth cause the most mistakes?

People get length and width right, then pick a box that is too shallow for the lid to close flat. Height is where soft goods fight you. A folded tee compresses, a stack of three does not, and a tissue-and-card layer adds more than it looks like. Measure the packed height, and if the product is squishy, size to the compressed height only if you are sure the customer will not receive it fluffed.

There is also the opposite error. Going one inch deeper than needed on a product you ship daily is more expensive over a year than most owners expect, once you count board, filler, and any size-based shipping charge. When in doubt between two heights, make the test box in the smaller one first.

When is a mailer the wrong choice?

A mailer suits retail orders a customer opens: apparel, beauty, subscriptions, gifting. It ships flat before use, needs no tape, and looks considered on arrival. It is the wrong box for heavy items, for glass or ceramics with no insert, and for anything going into a wholesale case, where a plain shipping carton is the better tool. If your order sounds like that, see our shipping box sizes guide. For goods that need a premium keepsake feel, compare it against a rigid box in mailer boxes vs rigid boxes.

For products that are fragile, ask about an insert. Our custom boxes with inserts page shows the options we offer. We do not recommend sizing the box tight enough to hold a fragile item by friction alone.

Which mailer style should I size for?

Style changes the usable height slightly, so choose it before you finalize size. A standard roll-front mailer is the everyday option. If you want a different opening and lid feel, look at ear-lock mailer boxes or luxury mailer boxes. Our mailer boxes guide and what is a mailer box cover how each one is built, and how to measure a box shows how to take the numbers. To see the full range, browse mailer boxes or our custom mailer boxes page. Cost drivers are in how much custom mailer boxes cost.

Questions buyers ask

Are mailer box dimensions inside or outside?

Inside, unless a supplier says otherwise. Mailer box sizes are normally written as internal length x width x height, because that is the space your product occupies. The outside measures a little more, usually by the board thickness on each side. Always confirm which one a quote uses before you approve it.

How much clearance should I leave in a mailer box?

Add about 1/8 to 1/4 inch in total to each dimension, not to each side. Use the smaller figure for a snug, flush fit and the larger one if you hand-pack with tissue or a card. Height needs the same allowance so the lid closes flat without bowing.

What is the most popular mailer box size?

10 x 8 x 4 inches is the size most ecommerce shops try first. It takes a folded garment, a small bundle of products or a modest gift set. 8 x 6 x 4 is the usual step down for smaller items, but use your own measurements before choosing either.

Is there a minimum order for custom mailer boxes?

No. We make custom mailer boxes with no minimum order, so you can order one box to test the fit or ten thousand for a full launch. Most people order a small run first, confirm the size with real stock, then reorder.

Can I get a mailer box in a size that is not on your chart?

Yes. Any internal dimension can be made to order, which is why the chart is a starting point and not a menu. Send the packed product dimensions and quantity and we return a dieline in that exact size to approve before anything prints.

How do I get a quote and dieline for my size?

Use the quote form and send your packed product measurements, board preference and quantity, even if it is one box. We reply with a dieline and a written quote. If you already hold a written quote for the same specs, we beat it.

How to order

Send the packed product dimensions and the quantity through the quote form, even if the quantity is one. We return a dieline in your internal size and a written quote. There is no minimum order. If you have the same specification quoted for less elsewhere in writing, we beat it. Design help, samples and shipping are free.