Two free tools in one. Enter your product dimensions to get a recommended box size and style, then calculate the dimensional (billable) weight carriers actually charge you. No sign-up, nothing stored — it all runs in your browser.
Enter your product's dimensions and how much protection it needs. We add the right clearance and suggest a box style.
Enter your packed box dimensions and its actual weight to see the billable weight by carrier.
Divisors used: UPS & FedEx domestic = 139, USPS Priority = 166. Billable weight = the greater of actual and dimensional weight, rounded up to the next pound.
Right-sizing the box is the cheapest shipping upgrade there is — a carton that hugs the product cuts the dimensional weight you pay on every parcel. That is exactly what a custom-sized box does versus an oversized stock carton. When you're ready, get a free quote with your dimensions and we'll send a dieline and 3D mockup.
Common internal dimensions for the box styles brands order most. Use these as a starting point, then fine-tune to your product with the finder above. We make any of these as a custom size at no die or plate charge.
| Use | Internal L × W × H (in) |
|---|---|
| Small (apparel, accessories) | 6 × 4 × 2 |
| Medium (shoes, books, kits) | 9 × 6 × 3 |
| Large (multi-item, subscription) | 12 × 9 × 4 |
| Flat (apparel, prints) | 10 × 8 × 1 |
See custom mailer boxes for builds and finishes.
| Use | Internal L × W × H (in) |
|---|---|
| Small parcel | 8 × 6 × 4 |
| Cube (versatile) | 10 × 10 × 10 |
| Medium | 12 × 10 × 8 |
| Large | 16 × 12 × 12 |
See custom corrugated boxes and pick a flute below.
| Carrier / service | Divisor (in³ per lb) | Notes |
|---|---|---|
| UPS — domestic | 139 | All package sizes |
| FedEx — domestic | 139 | All package sizes |
| USPS — Priority Mail | 166 | Zones 5–9, over 1 cu ft |
| UPS / FedEx — international | 139 | Same divisor, by carrier |
Flute is the wavy inner layer of corrugated board — it sets thickness and strength. Match it to how the box ships and prints.
| Flute | Thickness | Best for |
|---|---|---|
| E-flute | ~1/16" | Retail & mailer boxes; crisp print surface |
| B-flute | ~1/8" | Lightweight shipping, food boxes, good crush resistance |
| C-flute | ~3/16" | Standard shipping cartons; cushioning + stacking |
| BC double-wall | ~5/16" | Heavy or fragile freight; maximum strength |
Dimensional weight = (Length × Width × Height) ÷ divisor, with dimensions in inches and the result rounded up to the next whole pound. Carriers bill the greater of this and the scale weight, so a light-but-bulky parcel pays for the space it takes up. Note (effective Aug 2025): UPS and FedEx now round each dimension up to the next whole inch before multiplying — so a 7.2×5.1×3.4" box is figured as 8×6×4". This calculator applies that rule for UPS/FedEx; USPS uses the measured dimensions. Box size = product dimensions + clearance (0.25" snug, 1" standard, 2" cushioned) on each axis. These are public carrier formulas and standard packaging clearances — accurate as of 2026; always confirm current divisors with your carrier contract.
Multiply length × width × height in inches, divide by the carrier divisor (139 for UPS/FedEx, 166 for USPS Priority), and round up to the next pound. You're billed on the greater of actual and dimensional weight.
Take your product's L × W × H and add clearance: ~0.25" for a snug retail fit, 1" for standard void fill, or 2" when it needs cushioning all around. That gives your box's internal dimensions — exactly what the finder above outputs.
Because carriers charge the greater of scale weight and dimensional weight. A bulky, low-density box is billed on volume — so right-sizing the box is the most direct way to lower cost.
Yes. Dimensional weight is volume ÷ a fixed divisor, so trimming each dimension lowers the billable weight. A custom-sized box avoids paying to ship void space inside an oversized stock carton.