18 × 18 × 8 in box: dimensions, dim weight and strength
A 18 × 18 × 8 in box holds 2,592 in³ (1.5 ft³) inside. Made in C flute its outside is about 18.31 × 18.31 × 8.47 in, which dimensional weight bills USPS at 24 lb and FedEx at 19 lb.
Key numbers
| Inside (L × W × H) | 18 × 18 × 8 in |
|---|---|
| Inside volume | 2,592 in³ · 1.5 ft³ · 42.5 L |
| Inside, metric | 457 × 457 × 203 mm |
| Perimeter 2(L + W) | 72 in |
| Length + girth, C flute OD | 71.9 in |
Outside dimensions by flute
| Board | Caliper, in | Outside, in | Outside volume, ft³ |
|---|---|---|---|
| E flute | 0.063 | 18.13 × 18.13 × 8.19 | 1.557 |
| B flute | 0.125 | 18.25 × 18.25 × 8.38 | 1.614 |
| C flute | 0.156 | 18.31 × 18.31 × 8.47 | 1.644 |
| EB double wall | 0.188 | 18.38 × 18.38 × 8.56 | 1.673 |
| BC double wall | 0.281 | 18.56 × 18.56 × 8.84 | 1.764 |
OD ≈ ID + 2 calipers on length and width, + 3 on depth. An estimate: your box maker sets the scores. Convert other sizes.
Dimensional weight
| Carrier | Divisor | Measured, in (C) | DW, C flute | DW, BC double wall |
|---|---|---|---|---|
| USPS | 139 | 19 × 19 × 9 | 24 lb | 24 lb |
| FedEx | 139 | 18 × 18 × 8 | 19 lb | 24 lb |
DW = ⌈L × W × H ÷ divisor⌉ on outside dimensions, after each carrier's own rounding. USPS applies it only above 1,728 in³ (n/a means it bills actual weight). The carrier bills the greater of actual and dimensional weight. Divisors checked on carrier pages 2026-10-27; try your own weight.
Estimated compression strength
| Board | BCT, lbf | After 30 days storage |
|---|---|---|
| 32 ECT B flute | 564 | 338 |
| 32 ECT C flute | 630 | 378 |
| 44 ECT C flute | 866 | 520 |
| 48 ECT C flute | 945 | 567 |
| 48 ECT BC double wall | 1,268 | 761 |
| 61 ECT BC double wall | 1,611 | 967 |
| 71 ECT BC double wall | 1,876 | 1,125 |
Simplified McKee: BCT ≈ 5.87 × ECT × √(caliper × 72). The 30-day column applies Packgent's default 40% storage loss, an assumption. Estimates only; test with ASTM D642.
Pallet pattern on 48 × 40
| Board | Per layer | Layers | Boxes per pallet | Load height, in | Cube used |
|---|---|---|---|---|---|
| C flute | 4 | 6 | 24 | 56.3 | 65% |
| BC double wall | 4 | 6 | 24 | 58.6 | 70% |
Column stacked, no overhang, on a 48 × 40 in deck 5.5 in tall, loaded to 60 in overall. Those three are assumptions you can change in the pallet calculator. Pattern: 18.3125″ along the 48″ side.
Blank size in C flute
With one caliper allowance per score. Multiply board area by your board's combined weight (lb/MSF ÷ 1,000) for box weight, or use the box weight calculator.
Sources
- USPS Domestic Mail Manual 223 (Priority Mail prices and eligibility), section 1.4
- FedEx: What is dimensional weight?
- Flute calipers: Foster (1997), Wiley Encyclopedia of Packaging Technology
- McKee, Gander & Wachuta (1963), Paperboard Packaging 48(8)
Last reviewed . See all sources and how Packgent computes.
Have extra 18 × 18 × 8 boxes? Sell your surplus: tell us what you have and Packgent passes it to buyers in the Repackify network.