Courier Packaging Guide
Royal Mail, Evri & UK Courier Size Guides Explained
Choosing the right box size isn’t just about fit, it directly impacts your shipping costs, delivery success, and risk of surcharges.
This guide helps you align your packaging with Royal Mail, Evri, and courier size categories so you can standardise packing, avoid pricing jumps, and scale efficiently.
Find Out Your Shipping Costs
Courier Box Guide Calculator
Royal Mail & Evri Sizes Guides
Royal Mail Size Bands (What You Must Stay Within)
Letter
240mm × 165mm × 5mm
→ Documents only
Large Letter
353mm × 250mm × 25mm
→ Flat ecommerce, clothing, books
Small Parcel
450mm × 350mm × 160mm
→ Small boxed goods, shoes
Medium Parcel
610mm × 460mm × 460mm
→ Multi-orders, bulkier items
👉 These are fixed. There’s no flexibility.
Evri: More Flexible — But Not Unlimited
Evri pricing is weight-led, but size still matters.
Letterbox-friendly / Postable
→ Ideal for subscription boxes & low-value items
Standard & Large Parcels
Max length: 1200mm
Max combined size: 2450mm
Max weight: 15kg
👉 Go beyond these — and you’re into surcharge territory.
Take the Guesswork Out of Shipping
Choosing the Right Box
Before finalising your packaging, it’s worth checking:
- Are you using external dimensions (not internal)?
- Have you added packing allowance?
- Is there unnecessary empty space increasing your size?
Just as importantly:
- Oversized boxes increase costs
- Overfilled boxes increase dimensions
- Ignoring depth (especially 25mm limits) causes instant price jumps
Why This Approach Works
By working through this process:
- You remove guesswork from packing
- Your team can pack faster and more consistently
- Your shipping costs stay predictable
- Scaling becomes much easier
Ultimately, the right box size doesn’t just protect the product — it improves your entire fulfilment workflow.