Quick answer: In the UK, custom mailer boxes cost roughly £1.50–£3.50 per box at 50–100 units and £0.60–£1.20 at 1,000+, with minimums from 50 units. The smartest move is sizing your box to a Royal Mail band: keep it under 353×250×25mm to post as a large letter, or under 450×350×16cm for small parcel rates — the difference is worth pounds per order.
Common Mailer Box Sizes (and When to Use Them)
| Internal size (mm) | Typical use | Royal Mail band |
|---|---|---|
| 220 × 160 × 20 | Cards, prints, flat goods | Large letter |
| 240 × 180 × 50 | Cosmetics, small gifts | Small parcel |
| 305 × 220 × 80 | Subscription boxes, clothing | Small parcel |
| 350 × 250 × 100 | Multi-item orders, hampers | Small parcel |
| 400 × 300 × 150 | Larger bundles | Medium parcel |
Because QPack manufactures to your exact dimensions, you're not limited to stock sizes — and a made-to-measure box usually costs less to post than the nearest stock size up.
What Mailer Boxes Cost in 2026
- 50–100 units: £1.50–£3.50 each (full-colour digital print)
- 250–500 units: £0.90–£2.00 each
- 1,000+ units: £0.60–£1.20 each
Price depends mainly on size, board grade (E-flute is standard; B-flute for heavier items) and whether you print inside as well as outside. Inside print typically adds 15–25% but transforms the unboxing experience.
Sizing Rules That Save Money
- Measure your product, then add 5–10mm clearance per side — snug is protective and cheap.
- Check courier bands before finalising: a few millimetres can move you into a cheaper band.
- If you sell multiple product sizes, two well-chosen box sizes usually beat five.
- Letterbox-friendly boxes (under 25mm deep) avoid failed deliveries entirely.
What You Need to Get a Quote
Just three things: internal dimensions, quantity, and your artwork (or a brief — free design support is included). QPack quotes within 24 hours, prints from 50 units, and delivers UK-wide in 5–7 working days.
Get Your Mailer Box Quote
Tell us your product size and we'll recommend the exact box dimensions and cheapest postage band. Get a free mailer box quote or browse our custom mailer boxes to see options and finishes.