Find the right box size for anything you ship
Enter your product's measurements. The calculator adds cushioning and board thickness, then gives you the box's inside and outside dimensions, its dimensional weight and the flat sheet a box maker would cut.
How the box size is worked out
- Measure the product at its widest points. Include handles, caps, spouts and anything that sticks out. If the product already sits in retail packaging, measure the packaging.
- Add cushioning to every side. Cushioning goes on both ends of each measurement, so 1 inch of cushioning adds 2 inches to the length, width and height.
- That gives the inside dimensions. These are the numbers box makers quote and the size you order.
- Add the board thickness. Length and width each gain two walls. Height gains four layers, because the top and bottom flaps fold over each other.
- Check the dimensional weight. Carriers bill from the outside dimensions, so an oversized box can cost more to ship than the product weighs.
How much cushioning to leave
The right gap depends on how easily the product breaks and how it will travel. Parcel networks drop and stack boxes, so fragile items need more space for protective fill.
| Product type | Examples | Space on each side |
|---|---|---|
| Durable | Clothing, books, soft goods, plastic parts | 0 to ½ in (0 to 1.3 cm) |
| Standard | Boxed electronics, cosmetics, kitchenware | 1 in (2.5 cm) |
| Fragile | Glass, ceramics, candles, bottles | 2 in (5 cm) |
| Very fragile or high value | Instruments, lab glass, framed art | 2 in plus a second outer box |
Corrugated board thickness
Flute size sets the wall thickness. Exact caliper varies by mill and board grade, so treat these as typical values.
| Flute | Typical thickness | Common use |
|---|---|---|
| E-flute | 1/16 in (1.6 mm) | Mailer boxes, retail and printed product boxes |
| B-flute | 1/8 in (3 mm) | Product boxes and lighter shipping cartons |
| C-flute | 5/32 in (4 mm) | Most standard shipping cartons |
| BC-flute double wall | 1/4 in (6.5 mm) | Heavy, stacked or fragile shipments |
Inside and outside dimensions are not the same
A box listed as 12 × 10 × 8 inches has that much space inside. Its outside measures roughly 12⅓ × 10⅓ × 8⅔ inches in C-flute board. That difference is small, but carriers round each side up to the next whole inch, which can add a full pound or more of dimensional weight. Read the full explanation in inside vs outside box dimensions.
More tools: DIM weight calculator, box volume calculator and the standard box sizes chart.
More packaging calculators
- Mailer box size calculator
Size a branded mailer box around your product.
- Multi-item box calculator
The smallest box for several identical items.
- Boxes per pallet calculator
Boxes per layer, layers and total on a pallet.
- Freight class calculator
Density and estimated LTL freight class.
- Box compression strength calculator
Top-load strength with the McKee formula.
- Right-sizing savings calculator
What a better-fitting box saves each year.
See all calculators Read the blog
Frequently asked questions
What size box do I need for my product?
Measure the product's length, width and height at their widest points, then add your cushioning to both sides of each measurement. A 10 × 7 × 4 inch product with 1 inch of cushioning needs a box with inside dimensions of 12 × 9 × 6 inches.
Are box dimensions inside or outside measurements?
Box makers and stock box sellers normally list inside dimensions, because that's the space your product needs. Carriers measure the outside of the box, which is larger by the thickness of the board.
What order are box dimensions written in?
Length × width × height (also called depth). Length is the longer side of the opening, width is the shorter side of the opening, and height is the distance from the opening to the bottom.
How is dimensional weight calculated?
Multiply the outside length, width and height in inches, then divide by the carrier's divisor. UPS and FedEx commonly use 139 for daily rates and USPS uses 166. Carriers charge whichever is higher, dimensional weight or actual weight. Check your carrier's current rules before relying on a number.
What is a flat blank size?
It's the size of the corrugated sheet a box is cut from before it's folded. For a regular slotted container, the blank length is two lengths plus two widths plus a glue flap, and the blank width is the box width plus the box height.
Why is the closest stock box bigger than I need?
Stock boxes come in fixed steps, so the nearest one that fits often leaves extra space. That space needs more void fill and can push up dimensional weight. A custom box made to your exact inside dimensions removes it.