Box Size Guide: Picking the Right Shipping Box
5 min read
Measure the interior, length × width × height
Box dimensions always refer to the inside of the box, measured as length × width × height. Length is the longest side of the opening, width is the shorter side of the opening, and height (or depth) is the distance from the opening down to the bottom.
Leave room for cushioning
Don't size the box to your item exactly. For fragile goods, leave about two inches of space on every side to fill with cushioning so the item is suspended away from the walls. For sturdy, non-fragile items, a snug fit with minimal void is fine and ships more efficiently.
Single-wall vs. double-wall
Corrugated boxes come in single-wall (one layer of fluting) and double-wall (two layers) construction. Double-wall boxes resist crushing and punctures far better and are worth it for heavier or valuable contents.
- Single-wall: Most everyday shipments up to roughly 40–65 lbs, depending on the box's strength rating.
- Double-wall: Heavy items, fragile goods, or anything that will be stacked or handled roughly.
Why right-sizing saves money
Carriers bill by dimensional weight, so an oversized box can cost more to ship even when it's light. A box that's too big also lets contents shift and increases damage. Choosing the smallest box that still leaves proper cushioning room is the sweet spot for cost and protection.
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Frequently asked questions
Should a shipping box be bigger than the item or snug?+
For fragile items, slightly bigger — leave about two inches on every side for cushioning. For durable items, snug with little void space ships best and costs less.
What does ECT mean on a box?+
ECT (Edge Crush Test) measures a box's stacking strength. A higher ECT rating means the box resists crushing better, which matters for heavier contents and stacked shipments.
Can I reuse an old box?+
You can if it's still rigid, dry, and undamaged — remove or cover old labels and barcodes. Once cardboard is soft, crushed, or torn, it has lost much of its protective strength.