What Size Mailer Do I Need? A UK Guide for Small Sellers
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Quick answer: Pack your product as it will be sent, measure its length, width and thickness, then choose the smallest mailer that fits it comfortably with a little room to spare. Small 9 × 12" (about 23 × 30 cm) mailers suit accessories and smaller orders. Medium and Large mailers suit clothing and textiles. XXL sacks (33 × 66 × 10 cm) suit bulky or multi-item orders. Flat items like prints and A4 documents belong in a board backed envelope.
How do I measure for a mailer?
Measure the item the way it will leave your workshop, not the way it sits on your table.
- Pack it first. Fold clothing, wrap fragile pieces, and add any inner bag, tissue or card.
- Measure the packed item. Note the length, the width and the thickness at the thickest point.
- Allow a little extra. Choose a mailer a few centimetres longer and wider than your packed item, so it slides in and the seal closes flat.
- Check the usable space. Mailer sizes are external measurements. Glue lines and seams make the space inside slightly smaller, so do not choose a mailer that matches your item exactly.
Which mailer size should I choose?
| Mailer | Size | Best for | Smallest pack available |
|---|---|---|---|
| FSC Certified Paper Mailer, Small | 9 × 12" (24 × 30 cm) | Accessories and smaller orders | Pack of 10 |
| FSC Certified Paper Mailer, Large | 14 × 17" (36 × 43 cm) | Clothing, textiles and larger products | Pack of 10 |
| Compostable Mailer, Small | 9 × 12" (23 × 30.5 cm) | Accessories and smaller orders | Pack of 10 |
| Compostable Mailer, Medium | 12 × 16" (30.5 × 40.6 cm) | Clothing and mid-sized orders | Pack of 10 |
| Compostable Mailer, Large | 14 × 19" (35.6 × 48.3 cm) | Larger shipments, clothing and textiles | Pack of 10 |
| XXL Paper Mailing Sack | 13 × 26 × 4" (33 × 66 × 10 cm) | Bulky, oversized or multi-item orders | Pack of 10 |
| FSC Certified Board Backed Envelope, C5 or C4 | C5 and C4 envelope sizes | Documents, prints, photographs and artwork that must stay flat | Pack of 20 |
| FSC Certified Padded Paper Envelope | C5 | Smaller or more delicate items that need cushioning | Pack of 25 |
Should I size up or size down?
Pick the smallest size that fits properly. An oversized mailer uses more material than it needs to, and a mailer that is too tight can strain the seal. If your item sits between two sizes, go up one size, then look again at how you fold or wrap the item to see if the smaller size would work.
What if I sell items of different sizes?
Most small sellers need two or three sizes to cover their range. Start with the size you use most, then add one bigger size for larger orders. Packs start at 10 mailers, so you can stock a few sizes without a large order.
Our Sample Pack includes 11 pieces of ecommerce packaging, including all our compostable and paper mailer sizes except the XXL sack. You can test your own products in them before you order a full pack.
Frequently asked questions
What is the smallest quantity I can order?
Our mailers, XXL sacks and board backed envelopes start from small packs: 10 for the mailers and sacks, 20 for the board backed envelopes. This suits micro businesses and new sellers.
Are the mailer sizes internal or external?
The paper mailer sizes are external measurements, so the usable space inside is slightly smaller because of the glue lines and construction of the mailer.
What size is best for A4 items?
For A4 documents, prints and artwork that should not be folded, the C4 board backed envelope gives you room to pack them flat.
What size mailer do I need for clothing?
It depends on how thick your folded item is. Fold and pack one sample, measure it, then check it against the table above. Our compostable mailers and FSC certified paper mailers both come in sizes suited to clothing and textiles.
What if my order is too big for a standard mailer?
Use our XXL Paper Mailing Sack. It is made for bigger orders such as clothing, textiles, soft furnishings and multi-item parcels.
Last updated 3 November 2026.