Mailer Box Sizes: How to Pick the Right Size

Picking the wrong size is the most common mistake with custom mailer boxes. Too tight and the product scuffs or the lid will not close. Too loose and it slides around, needs extra filler and costs you more to ship. This guide shows how to measure your product, which sizes people usually start from, and how to avoid the usual errors.

How mailer box sizes are written

Box size is always written as length x width x height, and it refers to the inside of the box. Length is the longest side of the opening, width is the shorter side of the opening, and height is the depth from the base to the lid. If you mix up the order, your supplier may build the box on its side, so write the three numbers down in the same order every time.

Step 1: Measure your product

Measure the product itself, not its current packaging. Use a ruler or a tape measure and record the longest, widest and tallest points in inches. If the product is round, such as a candle jar, measure the diameter for both length and width. If you ship a set, lay everything out the way it will sit in the box and measure the whole group.

Step 2: Add room for protection

Add a small allowance on each side so the product slides in and out without force. For most products that means about 1/8 to 1/4 inch on length and width. If you use tissue paper, an insert or a thank you card, add that thickness too. Heavier or breakable items need more room for padding.

Common starting sizes

These are typical starting points, not fixed rules. Your own product measurements always decide the final size.

• 6 x 4 x 2 inches: small items such as a lip balm, a soap bar or a pair of earrings.
• 9 x 6 x 3 inches: a standard candle jar, a skincare bottle with a box, or a small gift set.
• 10 x 8 x 4 inches: larger gift sets or a few products packed together.
• 12 x 9 x 3 inches: flat items such as folded apparel, books or prints.

Step 3: Think about shipping weight

Carriers charge by weight and by box volume, so a box that is a little too large can raise your shipping cost on every order. Our free box size and dimensional weight calculator lets you check this before you place an order.

Common mistakes to avoid

• Measuring the outside of an old box instead of the product.
• Forgetting to include tissue, inserts or cards.
• Choosing a size that fits one product but not the whole set you plan to sell.
• Ordering a large quantity before seeing a mockup.

Not sure about your size?

Send us your product measurements, the box style you like and the quantity you need on our contact page. Orders start from 100 units, we prepare a free digital mockup for approval, and production takes 15 to 17 business days after design approval. If you need a more premium feel, you can also compare mailers with rigid boxes.