Custom mailer box sizes: a size chart with real prices

Custom mailer box sizes should start from your product, not from a size chart. Measure the thing going inside, add a little room, and make the box to those inside dimensions. As a first guess, a single small product like a candle or a skincare bottle fits around 6 x 4 x 2 inches, a two- or three-piece set or a folded tee around 9 x 6 x 3, and a subscription box around 12 x 9 x 4. The six sizes below each come with what usually fits and what it costs at 250, 500, and 1,000 boxes.

There isn't an official standard mailer size you have to pick from. Every custom mailer is cut from a flat sheet to your measurements, so the size is whatever your product needs. But a handful of sizes cover a lot of ground, and seeing them side by side with real prices makes the decision much easier.

Common custom mailer box sizes and what fits

Every size here is an inside measurement, written as length x width x depth. Inside is what matters, because it's the space your product actually gets.

If your product sits between two rows, you don't have to round up to the next one. You get the size in between. That's the whole point of a custom box.

What each size costs

These prices come straight from our estimator for a full colour mailer with no finish. You'll get the same numbers on the custom mailer boxes page if you type in the same dimensions.

Two things stand out. First, a bigger box costs more, but not in proportion. The 12 x 9 x 4 holds more than twice the space of the 9 x 6 x 3 and costs about 40% more at the same quantity. Second, quantity moves the price more than size does. The large box at 1,000 is cheaper each than the medium box at 250.

Which size for which product

Here's where we'd start for the kinds of products people commonly send in a mailer. Treat these as a first guess to measure against, not a rule.

Skincare and cosmetics. A single bottle or jar sits happily in a 6 x 4 x 2. A cleanser, serum and cream together usually wants the 9 x 6 x 3, often with a card insert so the bottles don't knock together. Our page on mailer boxes for cosmetics has more on what beauty brands order.

Candles. One candle in a jar or tin fits a small mailer, but check the depth with the lid on, because a candle is often taller than it is wide. For a set of three, the 10 x 8 x 4 with an insert is a sensible starting point. Glass needs cushioning room, so add the extra half inch per side. See mailer boxes for candles.

Apparel. A folded tee fits a 9 x 6 x 3, and a hoodie or a two item bundle is more comfortable in a 12 x 9 x 4 or 14 x 10 x 4. Soft goods don't fold perfectly flat, so leave closer to an inch rather than a quarter. More on mailer boxes for apparel.

Coffee. Bags vary a lot by brand, but a single 12 oz bag often fits a small wide 8 x 6 x 2 lying flat, or a 9 x 6 x 3 standing up. Two bags together are closer to a 10 x 8 x 4. Measure a filled bag, not an empty one. See mailer boxes for coffee.

Subscription boxes. These change every month, so size for the biggest month you've actually planned, not every possible product. The 12 x 9 x 4 is a reasonable start because it holds three or four mixed items with some tissue. More on subscription mailer boxes.

How to pick the right size

1. Measure the product at its widest points. Take the longest, widest and deepest measurements, including any cap, pump, handle or bow. Use a ruler or calipers, not a guess from the product listing. Our guide to measuring a box properly goes through it step by step.
2. Add the right amount of room. How much depends on what you're packing, shown just below.
3. Count everything else that goes in. Tissue, a thank you card, a sample sachet, crinkle paper. Each one takes depth. If you're planning an insert, size the box around the insert rather than the bare product.
4. Check it against a real sample. Numbers on paper are one thing. Your product sitting in real board is another.

How much room to add:

• Rigid products such as jars, bottles and electronics: about a quarter inch per side, so the item slides in and out without a fight.
• Soft goods such as folded apparel: closer to an inch, because fabric doesn't pack flat and a tight box crushes it.
• Fragile items that need cushioning: half an inch to an inch per side for tissue, paper fill or an insert.

Inside vs outside dimensions

This one is easy to get wrong on a first order. A mailer is made from E flute corrugated board, which is about a sixteenth of an inch thick. So the outside of the box is a little bigger than the inside on every side, and the lid adds a little more on top.

That sounds small. But if you give us outside numbers thinking they're inside numbers, your product won't fit, and a run of boxes that's a size too small can't be used at all. When you send us a size, always send the inside, and we'll work out the rest.

Why box size changes your shipping bill

Carriers don't only charge by weight. For bigger parcels they charge by dimensional weight, which is the length times width times height, divided by a fixed number. If that figure is higher than what the parcel actually weighs, you pay the higher one.

Here's a detail that matters for mailers. USPS only applies dimensional weight to packages over 1,728 cubic inches, which is one cubic foot, and from July 12, 2026 it divides by 139 and rounds every fraction of an inch up to the next whole inch. That's straight from the USPS notice on the change (opens in a new tab).

Now look at the sizes above. The largest, 14 x 10 x 4, is 560 cubic inches inside. Even with the board added, every size in this post is well under a cubic foot, so on USPS you pay for the actual weight. UPS and FedEx are different: they apply dimensional weight to every package, however small, and our post on dimensional weight and box size runs the numbers across carriers. If your product needs a shipper instead, our shipping box sizes chart shows which sizes stay under the USPS cubic price tiers.

Size still matters for the box itself. Going from 12 x 9 x 4 down to 10 x 8 x 4 saves about $0.26 a box at 500, before you count any shipping.

Mistakes that cost you money

• Sending outside dimensions. Covered above, and worth saying twice.
• Forgetting the insert. An insert takes up space on every side it touches. If you decide on one after the box is sized, the product may no longer fit. Decide first, then size the box around both.
• Measuring the product without its own packaging. A jar often goes into the mailer inside its own carton. Measure what actually goes in the box.
• Going too big. You pay for it three times: more board in the box, more tissue or paper fill to stop the product moving, and a bigger parcel that is closer to the size where carriers start charging for space. A box with lots of empty space also lets the product slide, and sliding is what breaks things in transit.
• Going too tight. The opposite mistake costs money too. If the product has to be forced in, packing takes longer, corners get crushed, and a glass jar has nothing between it and the wall of the box. A quarter inch per side for a rigid item is there for a reason.
• Running a different size for every product. If you sell three items of a similar size, one box that fits all three with a simple insert is usually cheaper than three separate runs. Fewer sizes means bigger quantities, and bigger quantities are where the price drops.
• Ordering before holding it. If you're unsure, order a sample pack and put your product next to real board before you commit.

Our pick for a first order

If you're launching one product and you're not sure, start from the medium, 9 x 6 x 3, and adjust it to your own measurements. It fits a lot of common first products, from a skincare set to a folded tee, and at 500 boxes it's $1.57 each.

Order 250 or 500 first, see how it works with your real product and your real courier, then adjust the size on the reorder if you need to. First orders often get something slightly wrong, and a small first run keeps that mistake cheap.

Key takeaways

• Custom mailer box sizes are made to your product's inside measurements. There's no standard size you're forced to pick.
• The six sizes here run from 6 x 4 x 2 to 14 x 10 x 4 inches.
• A 9 x 6 x 3 full colour mailer is $2.21 each at 250 and $1.57 at 500.
• Quantity moves the price more than size does.
• Always give inside dimensions, and add about a quarter inch per side for rigid products.
• All six sizes are under one cubic foot, where USPS starts charging dimensional weight.

Common questions