How to Measure a Kraft Box: Inside Sizes and Clearance

Why do inside sizes matter more than outside sizes?

Your product sits inside the box, so the inside is the only size that decides whether it fits. Outside sizes change with the board, while inside sizes stay tied to the product.

We make every kraft box from the inside size you send, in millimetres. If you send an outside size by mistake, the box comes out smaller inside than you expect, by twice the board thickness on each side.

That gap is tiny on a soap carton and large on a double wall carton. Getting into the habit of inside sizes saves a lot of back and forth.

What do length, width and height mean on a box?

Sizes are written as L × W × H. Length is the longer side of the opening. Width is the shorter side of the opening. Height is the depth from the opening down to the base.

The order matters because it tells us where the opening sits. A 250 × 180 × 80 mm mailer opens on its broad top. A tuck carton written 70 × 70 × 150 mm opens at the narrow end, with the 150 mm running up the side.

If you are unsure which face should open, say how the product goes in. For example, a bottle dropped in from the top, or a shirt laid flat into a tray.

How do you measure your product in seven steps?

1. Use a steel rule or digital calipers rather than a soft tape, which bends around corners.
2. Measure the product as it will actually be packed, including any lid, pump, ribbon or tissue wrap.
3. Measure the widest point on each side, such as the shoulder of a bottle or the rim of a jar lid.
4. Write the three numbers in millimetres, longest first for the opening, then the depth.
5. Add clearance on each measurement using the table in the next section.
6. If an insert, divider or padding goes in too, add its thickness before the clearance.
7. Send the final inside size, plus a product photo, so we can check the fit on the proof.

Measuring the packed item rather than the bare one matters most on mailers. A folded jumper in tissue can be 10 mm taller than the jumper alone. That is why our kraft mailer boxes for posting orders are sized to the packed order.

How much clearance should you add?

Clearance is the small space between your product and the inside wall. Too little and the product jams or splits a corner. Too much and it rattles, scuffs and looks lost.

The figures below are typical starting points used across the trade. Add them to the product size on each side of the measurement, not once overall.

When in doubt, send the bare product size and tell us how it is packed. We add the clearance on the proof and you can adjust it before printing.

How does board thickness change the outside size?

Every wall adds board thickness to the outside. A simple rule is outside size equals inside size plus two board thicknesses on length and width, and a little more on height where flaps overlap.

With folding kraft at about 0.5 mm, the difference is only around 1 mm per side. With E flute at about 1.5 mm, a 250 × 180 × 80 mm mailer grows to about 253 × 183 × 85 mm outside. With B flute at about 3 mm, the same inside size grows by roughly 6 mm on length and width.

Double wall carton board is about 6–7 mm thick. A 450 × 350 × 300 mm inside size can measure about 13 mm more on each side outside.

Outside sizes matter for postage bands, shelf space and fitting cartons into an outer. If you have a limit, such as a parcel band or a shelf depth, send it with your brief and we size the inside to suit.

What sizes do common products start from?

These are typical starting sizes from our own range, given as inside sizes in millimetres. They are guidance only, because every box is made to your product.

• A standard soap bar often fits a carton about 90 × 65 × 30 mm.
• A large jar candle often needs about 100 × 100 × 110 mm.
• A folded T-shirt usually suits an inside size near 280 × 220 × 50 mm.
• A pair of men's shoes often starts at about 330 × 200 × 120 mm.
• An A3 print rolled for posting suits a tube about 320 mm long with a 60 mm diameter.

Bars vary a lot in thickness, so measure yours. Our kraft soap boxes for handmade bars are made to the bar, from small guest bars to large slabs.

How do you measure round and odd-shaped products?

For a jar or tin, measure the diameter at its widest point, usually the lid, plus its total height, lid included. A square box then uses that diameter for both length and width.

For a round box or tube, the diameter becomes the inside diameter. Add about 1–2 mm so the product slides in without forcing.

Odd shapes, such as a curved bottle, a brush set or a gift hamper, are easiest to size from a photo. Lay the item on squared paper or beside a ruler and photograph it from above and from the side.

Jar candles are a common case where the lid is wider than the glass. Our kraft candle boxes for jar and pillar candles are sized to the lid, then checked on the proof.

How do inserts and windows change the measurements?

An insert takes up room on every side it touches. A card insert at about 0.5 mm barely moves the size, but a corrugated insert can take 3 mm or more from each wall.

Measure the product sitting in its insert, or send the product size and let us draw the insert around it. For sets, give each item its own size and say how you want them laid out.

Windows do not change the inside size, but they affect where the product should sit. Keep the part you want on show at least 10 mm from the window edge so the board frame does not hide it.

Kits and gift sets are where this matters most. Our kraft mailer boxes with fitted inserts are drawn around each item, so send every size in the set.

What measuring mistakes cause boxes that do not fit?

Sending outside sizes as inside sizes is the most common one. The second is forgetting the lid, pump or cap, which can add 10 to 20 mm to a bottle.

Another is mixing up width and height, so the box opens on the wrong face. A tuck carton made 150 × 70 × 70 mm opens on its long side instead of the end.

Shoes and boots catch people out as well. Measure the box the shoes already come in, or the shoes with tissue, not one shoe on its own. Our kraft shoe boxes for trainers and boots are measured around both shoes lying together in tissue.

What should you send with your size?

Send the inside size in millimetres as L × W × H, the product name, and a photo if you have one. Tell us if it goes through the post by itself, stands on a shelf or packs into a bigger carton.

Add your print plan and any extras, such as a window, insert or handle. Each of those can change the size slightly, and we account for it on the dieline.

Prices on the written quote begin from £0.25 per unit, and bigger boxes or extra inks raise that figure. The free design proof shows the box with your measurements before anything is cut. Making the boxes takes 4–6 business days from approval, with free tracked UK delivery in a further 2–3 business days. You can send your box size for a quote today.