# Packrift packaging guide

Practical rules for choosing and sizing shipping packaging. Packrift's tools apply these rules automatically; this page explains them.

## Box or mailer?

| Item | Best packaging |
|---|---|
| Apparel and soft goods that cannot break | Poly mailer: lightest and cheapest to ship |
| Small items that need light protection (books, cosmetics, accessories) | Bubble (padded) mailer, for items up to about 2.5 in thick |
| Flat items that must not bend (prints, photos, documents) | Rigid or paperboard mailer |
| Small items where presentation matters (subscription, retail orders) | Corrugated mailer box |
| Fragile, heavy, stacked or odd-shaped items | Corrugated shipping box |
| Posters, prints and long narrow items | Mailing tube |

## Size the box

- Corrugated box sizes are inside dimensions, listed length x width x depth. The opening is length x width.
- Leave cushioning space on every side: about 1/2 in for sturdy items, 1 to 2 in for electronics, and 2 in for fragile items, with the item wrapped and every gap filled.
- For very fragile items, box the item, then pack that box inside a larger box with 2 to 3 in of cushioning between them.
- A snug box ships cheaper. Extra space costs dimensional weight and needs more void fill.

## Size a mailer

- Poly and bubble mailers are listed width x length. The width must fit the item's width plus its thickness, and the length must fit the item's length plus its thickness, with about 1 in to spare for the seal.
- Poly mailers: 2 to 2.5 mil suits apparel; 3 to 4 mil adds tear and puncture resistance.

## Box strength

The edge crush test (ECT) rating sets how much weight a box is rated to carry, per the standard box maker's certificate:

| Board | Max weight (box and contents) | Max outside size (length + width + height) |
|---|---|---|
| ECT-32 single wall | 65 lb | 75 in |
| ECT-40 single wall | 80 lb | 85 in |
| ECT-44 single wall | 95 lb | 95 in |
| ECT-48 double wall | 100 lb | 95 in |
| ECT-51 double wall | 120 lb | 105 in |
| ECT-61 double wall | 140 lb | 110 in |
| ECT-71 double wall | 160 lb | 115 in |

Stay well under the rating when boxes are stacked, shipped by freight or packed with dense items.

## Dimensional weight

Carriers bill the greater of actual weight and dimensional weight:

- UPS and FedEx: the outside length x width x height in inches, each side rounded up to the next inch, divided by 139. This applies to every package, including filled poly mailers.
- USPS: the same calculation (divide by 139, each side rounded up, since July 12, 2026), but only for packages over one cubic foot (1,728 cubic inches). Smaller USPS packages bill by actual weight.

Box sizes are listed as inside dimensions, so measure the outside: add about 1/4 in to each side of a corrugated box. A listed 12 x 12 x 12 box is about 12.25 in outside, rounds up to 13 x 13 x 13 and bills as 16 lb with UPS, FedEx and USPS even when it weighs 3 lb. A listed 10 x 8 x 6 box rounds up to 11 x 9 x 7 and bills as 5 lb with UPS or FedEx; with USPS it bills its actual weight. Right-sizing the box is usually the biggest shipping saving.

## Tape

- 2 in tape suits light and medium boxes; 3 in tape suits heavy boxes and warehouse use.
- Acrylic tape is quiet and clear and holds in heat, cold and sunlight. Hot-melt tape grabs fast and holds best on recycled or dusty cartons.
- Tape the center seam and both edge seams (an H pattern) on the top and bottom of heavy boxes.

## Void fill

- Air pillows: light fill for sturdy items.
- Kraft paper: blocking and bracing; curbside recyclable.
- Bubble wrap: 3/16 in for surface protection, 1/2 in for cushioning.
- Foam: the most protection for fragile items.

## Heat-sensitive items

- Candles, chocolate, cosmetics and some adhesives soften in summer heat; many container candle waxes soften around 115 to 125°F, which a delivery truck can exceed.
- Ship early in the week so parcels do not sit in a truck or depot over the weekend, and use faster services during heat waves.
- Insulated mailers or box liners with cold packs protect chocolate and other goods that melt at lower temperatures.

## Stretch film

- Hand film around 60 to 70 gauge suits light, stable loads; 80 gauge suits most pallets; 90 to 120 gauge suits heavy or sharp-edged loads.
- Cast film is quieter and clearer; blown film is stronger and more puncture resistant.

## Ordering from Packrift

- Prices are per pack, and each product title states the pack count.
- Volume discounts apply automatically at checkout, and so does free shipping when an order qualifies; Packrift's tools show the current tiers and whether an order qualifies.
- For pallet quantities, custom sizes or printing, request a quote at https://packrift.com/pages/bulk-quote.