Royal Mail Format Checker

Enter your item's dimensions and weight to find out its format and approximate postage cost.

2nd Class:
1st Class:
Prices are approximate and include current Royal Mail rates as of 2026. Always verify current rates at royalmail.com.

Need to resize your shipping label? Once you know your format, use the Label Resizer to get your label print-ready.

Understanding Royal Mail Formats

Royal Mail uses four main formats to determine postage rates. Getting the right format saves money and ensures faster delivery.

Letter

The smallest and cheapest option for flat items.

  • Max length: 240mm
  • Max width: 165mm
  • Max thickness: 5mm
  • Max weight: 100g

Large Letter

For items that don't fit in a standard letter envelope.

  • Max length: 353mm
  • Max width: 250mm
  • Max thickness: 25mm
  • Max weight: 750g

Small Parcel

For parcels up to 2kg, with compact dimensions.

  • Max length: 450mm
  • Max width: 350mm
  • Max depth: 160mm
  • Max weight: 2000g

Medium Parcel

Larger parcels up to 20kg.

  • Max length: 610mm
  • Max width: 460mm
  • Max depth: 460mm
  • Max weight: 20kg

Pro Tip: The Large Letter Trap

Many sellers overpay by sending items as Small Parcels when they'd fit in a Large Letter. If your item fits the Large Letter dimensions, use that instead — you'll save significantly on postage costs and often get faster delivery.

Frequently Asked Questions

What if my item exceeds Medium Parcel limits?

You'll need Royal Mail Special Delivery or a specialist courier like DPD or FedEx. Special Delivery is tracked and guaranteed next-working-day.

Can I send a Large Letter through a letterbox?

Yes, if it's up to 25mm thick. Royal Mail will attempt letterbox delivery for items in Large Letter format up to that thickness.

What's the difference between 1st and 2nd Class?

1st Class is faster (usually next working day) and more expensive. 2nd Class is slower (2–3 working days) but significantly cheaper. Choose 2nd Class for non-urgent items to reduce postage costs.

Do I need insurance for a Medium Parcel?

Standard Royal Mail compensation is limited. For valuable items, consider buying additional insurance or using a tracked service like Special Delivery Guaranteed.

How accurate is this tool?

This tool uses the official Royal Mail format specifications. However, Royal Mail may occasionally update requirements or apply edge-case rules, so always verify with royalmail.com before sending high-value items.