What size box do I need?
Choosing a box by eye usually ends one of two ways: it doesn't close, or it's so big you're paying to ship air. There's a simple method that gets it right the first time, and it works for anything from a candle to a computer monitor.
Step 1: Measure the product properly
Measure length, width and height at the widest points. Include anything that sticks out: handles, pump tops, cables, hang tags. If the product already has its own retail box, measure that box, because it's what will go into the shipper.
Irregular shapes are measured as the smallest rectangle they fit inside. For several items packed together, arrange them the way you'll actually pack them and measure the group.
Step 2: Decide how much cushioning it needs
Cushioning goes on every side, so it's added twice to each dimension. A reasonable starting point:
| Product | Space on each side |
|---|---|
| Durable (clothing, books, plastic goods) | 0 to ½ in |
| Standard (boxed electronics, cosmetics) | 1 in |
| Fragile (glass, ceramics, candles) | 2 in |
| Very fragile or valuable | 2 in plus a second box |
Step 3: Add it up to get the inside dimensions
Product dimension + (2 × cushioning) = box inside dimension. A 10 × 7 × 4 inch product with 1 inch of cushioning needs a box that is 12 × 9 × 6 inches inside. That's the size you order, because box sizes are always quoted as inside dimensions.
Step 4: Check the outside size
The walls add to the outside. In standard single-wall board, expect the outside to be about ⅓ inch longer and wider and about ⅔ inch taller. Carriers measure the outside, so this is what determines dimensional weight.
Step 5: Compare with stock sizes
Stock boxes come in fixed steps. If a stock size is within half an inch or so of what you need on each side, it's usually the cheapest option. If the nearest stock size is inches too big, you'll pay for extra fill and possibly a higher dimensional weight on every shipment, and a custom size becomes worth pricing.
Getting the orientation right
Box dimensions are always length × width × height. Length and width describe the opening, height is the depth. A 12 × 6 × 10 box and a 12 × 10 × 6 box have the same volume but very different openings. Think about how the product goes in. Flat items usually want a wide opening and shallow depth.
A quick example
A ceramic vase measures 6 × 6 × 11 inches. It's fragile, so allow 2 inches per side: 10 × 10 × 15 inches inside. There's no common 10 × 10 × 15 stock box, but 10 × 10 × 16 or 12 × 12 × 16 might be. The 10 × 10 × 16 adds an inch of fill at the top, which is fine. The 12 × 12 × 16 is noticeably bigger and would increase dimensional weight.
When one size doesn't fit all
If you sell many products, you don't need a box for each. Most shops get by with a handful of sizes chosen to cover their range with little empty space. Measure your top sellers, calculate each ideal size, then look for sizes that serve several products at once.