The regular slotted container is the most-made box style in the world, and it has one governing rule: all four flaps are cut to the same length, and that length is half the box width. Understand that and the rest of RSC sizing is arithmetic.
Why the flaps are half the width
The two outer flaps fold in from the long sides and are meant to butt together at the centre line. If they are half the width each, they meet exactly. That is the whole design. It also means the flap geometry is decided by the width, so the moment you change the width you change how the box closes.
- When width and depth are close, the box closes neatly and uses board efficiently. This is the sweet spot.
- When the width is much greater than the depth, the flaps are long relative to the side panels and you get a lot of doubled board across the top, which is wasteful but strong.
- When the width is much less than the depth, the flaps are short and the box is a tall tube with a small closure, which is the shape most likely to burst at the seam under load.
The blank size, and why footprint shape costs money
A flat RSC blank is approximately:
| Blank dimension | Approximate formula |
|---|---|
| Along the score line | 2 x (length + width), plus a glue or joint tab allowance |
| Across the panels | Depth + width (half the width for each set of flaps, top and bottom) |
Run two boxes of identical volume through that and the squarer one uses less board. A 20 x 4 x 4 inch box and a 10 x 8 x 4 inch box hold the same volume, but the long one has a much larger perimeter and therefore a much larger blank. If you have freedom over the arrangement of the contents, arranging them into a squarer footprint is a direct material saving on every unit.
Getting your dimensions
- Measure the packed load at its widest in each axis.
- Add the void fill or insert thickness on each face.
- Write the two opening dimensions with the longer one first. That is your length and width. The remaining figure is the depth.
- Label the whole thing internal, and ask for written confirmation that the quote is internal too.
- Sanity-check the width against the depth using the three cases above.
When an RSC is the wrong style
RSC is the default, not the answer to everything.
- Very shallow and wide, like a framed print or a flat display: a full overlap or a telescoping two-piece handles it better, because RSC flaps that are enormously longer than the panel just buckle.
- Heavy and stacked: full overlap flaps double the board across the whole top and bottom, which is where the compression goes.
- Frequently reopened: a tuck top or a lid and base is a nicer experience than a taped RSC that has to be cut open.
- Retail-facing: an RSC is a transit box. If the customer sees it, a mailer style with a printed interior does more work.
Board, print and ordering
Flute grade follows the packed weight of one box and the stack height on a pallet. C flute at about 3/16 inch is the ordinary shipping default, with double wall for heavy or tall stacks. On print, ink coverage moves corrugated pricing more than buyers expect: one or two colours on natural kraft is the cheapest and reads as deliberate, while full coverage on a white liner is the expensive end.
Minimum order is 100 boxes, and pricing starts from about $0.48 per unit at bulk volumes, confirmed on your written quote. The die, the plates, design support, US shipping and a digital proof before anything prints are included, so the exact internal dimension you calculated costs no more to tool than a standard-sounding one. Production runs from West Chicago in the US and Guangzhou in China, with turnaround quoted per product in three lanes: rush (expedited production plus air freight), standard (air) and cost saver (sea), from about 7 business days plus 2 to 5 for delivery.
Order at corrugated boxes, and if you have not yet settled the load measurement, start with how to size a corrugated shipping box.
Send us the internal dimension and the packed weight through the quote form and we will confirm the board grade and price it in writing.
