Box size calculator
Tell us what you are packing and how much padding it needs, and this works out the smallest box that holds it. For several identical items it tries every sensible arrangement and keeps the smallest box it finds.
How this calculator works
- For a single item, the answer is the item plus twice your padding on each measurement.
- For several, it tries every whole-number grid that holds the quantity — two across and three deep, six in a row, and so on — in every orientation the item is allowed to take.
- It keeps the arrangement that produces the smallest box.
- Your padding is then added around the outside of the whole group.
This is a search over rectangular arrangements, not a general packing solver. It will not find a clever interlocking arrangement, and it does not claim to. What it gives you is a box size that definitely works, with the arrangement shown so you can check it against reality.
Worked example
Four 4 × 4 × 4 inch boxed mugs, no extra padding.
- A 2 × 2 × 1 grid gives an 8 × 8 × 4 in box, which is 256 cubic inches.
- A 4 × 1 × 1 row gives 16 × 4 × 4 in, also 256 cubic inches, but a far worse shape.
- Both hold all four items with no waste, so the calculator prefers the squarer one — a lower length plus girth, and less likely to hit a size surcharge.
Edge cases worth knowing
- Quantities that do not tile evenly leave spare slots. Five items might need a six-slot arrangement. The result says when that happens.
- Padding goes around the group, not each item. If every item needs its own wrap, add that to the item measurements instead.
- These are internal measurements. Box sellers list the outside, so look for a box whose inside is at least this size.
- Real boxes flex and items compress. A recommendation with no slack is harder to pack than the numbers suggest.
- Mixed items are a different problem. This assumes every item is identical. For a mixed order use the packing estimator.
Common questions
- Is this the mathematically smallest possible box?
- It is the smallest box among rectangular grid arrangements, which is what almost everyone packs in practice. A true optimal solver could occasionally do better with an irregular arrangement, and we do not claim to be one.
- How much padding should I use?
- Half an inch per side for sturdy goods, two inches per side for fragile ones. Two inches of padding adds four inches to every measurement, which is often the difference between one box size and the next.
- Why did it pick a square-ish box over a long one?
- When two arrangements have the same volume, the squarer one wins. It has a lower length plus girth and is less likely to attract a size surcharge.
- Can I stop it stacking my items?
- Yes — choose "one layer only". That forces a single layer even when stacking would give a smaller box.