A regular slotted container (RSC) is the standard shipping box: one piece of corrugated, four flaps top and bottom, all of them the same depth. Its size is always written internal length x width x depth. Length and width are the two sides of the open top, length being the longer one, and depth is the measurement from the top score down to the bottom score.
Why internal and external are different numbers
Corrugated has thickness, and that thickness sits on every wall. If you ask for a 12 x 10 x 8 in box and the supplier reads that as internal, the outside will measure roughly 12.4 x 10.4 x 8.4 in on single wall C flute. That gap matters when you are counting cases onto a pallet or into a shelf. Put the word internal or external next to every number on your spec, and check which one the quote is answering.
| Flute | Approximate caliper | Added per opposing pair of walls |
|---|---|---|
| E | About 1/16 in | About 1/8 in |
| B | About 1/8 in | About 1/4 in |
| C | About 3/16 in | About 3/8 in |
| A | About 1/4 in | About 1/2 in |
| BC double wall | About 5/16 in | About 5/8 in |
Those calipers are the published industry profiles, not an iBox stock list. Board varies slightly between mills, so treat them as starting points and confirm the finished caliper on your quote.
The blank size, and why odd depths are cheap but odd widths are not
Because every RSC flap is half the box width, the flat blank works out at (2L + 2W + glue tab) wide by (D + W) tall. Depth only affects one of those numbers, so making a box deeper uses relatively little extra board. Widening it costs board twice over, once in the perimeter and once in the flap length. If you are trimming material out of a carton, take it out of the width first.
Sizing the box to the product
- Measure the product at its widest point in all three axes, not at its nominal size.
- Add clearance for whatever goes around it. A thin poly bag needs very little. A moulded insert or 2 in of void fill on each face needs exactly that much.
- Write the result as internal length x width x depth.
- Check the footprint against the pallet before you commit.
Fitting the pallet
The standard North American pallet is 48 x 40 in. A footprint that divides into both numbers fills a layer with no overhang and no wasted deck. A 12 x 10 in footprint gives 16 cases per layer. A 16 x 10 in footprint gives 12. A 24 x 20 in footprint gives 4. Overhang is the expensive mistake here, because a case that hangs off the deck edge loses a large share of its stacking strength. If you are unsure which board grade you need under a tall stack, the comparison on single wall vs double wall corrugated covers the trade.
Ordering, minimum and turnaround
Custom RSCs start at 100 boxes, from about $0.48 per unit at bulk volumes, confirmed on your written quote. The cutting die, the printing plates, design support, US shipping and a digital proof are included, which is the reason a genuinely custom internal size is not a premium option here: there is no tooling charge to avoid. Turnaround is quoted per product across three lanes, rush (expedited production plus air freight), standard (air) and cost saver (sea), starting from about 7 business days of production plus 2 to 5 days for delivery. Rush carries a premium of roughly 7 to 25% depending on the job. iBox Factory runs two plants, West Chicago in the US and Guangzhou in China, and the lane you pick determines which one makes sense.
If you already know the product measurements, send them with a note saying whether they are internal or external and we will come back with a board grade and a price. Start at request a quote, or read the format options on the corrugated boxes page if you want to order a stock style instead.
