Postal / Postage Stamps

Postal / Postage Stamps: What They’re For and When to Use Them

Postal stamps are a simple way to pay postage for everyday mail. This category focuses on three common UK stamp types used for domestic sending: Standard 1st Class, Standard 2nd Class, and Large 1st Class. Choosing the right stamp is mainly about matching your item to the correct size format (Letter vs Large Letter) and staying within the maximum thickness and weight limits for that format.

For most senders, the key is understanding how Royal Mail defines a “Letter” and a “Large Letter.” A Letter can be up to 24cm x 16.5cm and 0.5cm thick, with a maximum weight of 100g. A Large Letter can be up to 35.3cm x 25cm and 2.5cm thick, with a maximum weight of 750g. These size bands are what determine whether you should use a standard letter stamp or a large letter stamp.

Postal / Postage Stamps — Helpful Guide

This guide explains the stamp options in this collection and how they relate to common mail formats. It also links directly to the products available in this category so you can quickly compare what you need.

1) Standard Letter Stamps (for “Letter” format)

Standard letter stamps are intended for items that qualify as a Letter: up to 24cm x 16.5cm, up to 0.5cm thick, and up to 100g. Typical examples include single sheets of paper, folded letters, greeting cards, and thin documents in a slim envelope. If your envelope becomes too thick (for example, due to multiple inserts or rigid contents), it may no longer qualify as a Letter even if the length and width are within limits.

• Standard 1st Class Stamps. Use for standard letters when you want the 1st Class service level (often chosen for time-sensitive letters and documents).
• Standard 2nd Class Stamps. Use for standard letters when delivery speed is less critical and you’re sending routine mail.

2) Large Letter Stamps (for “Large Letter” format)

Large letter stamps are designed for items that qualify as a Large Letter: up to 35.3cm x 25cm, up to 2.5cm thick, and up to 750g. This format is commonly used for thicker document packs, magazines, catalogues, and flat merchandise that still fits within the Large Letter thickness limit. The thickness allowance is the main difference: 2.5cm provides much more flexibility than the 0.5cm limit for Letters.

• Large 1st Class Stamps. Use for large letters when you need the 1st Class service level and your item is too large or thick to qualify as a standard Letter.

Common Use Cases (Practical Examples)

Sending a single letter or a thin document

If your mailpiece is a typical envelope with a few sheets of paper and it stays within 24cm x 16.5cm and 0.5cm thickness, it fits the Letter format. In that case, a standard letter stamp is appropriate. The choice between 1st and 2nd Class is usually based on how quickly you need it delivered.

Sending a greeting card

Most greeting cards in a standard envelope qualify as a Letter, but cards with bulky decorations or multiple inserts can exceed the 0.5cm thickness limit. If the envelope becomes too thick, it may need to go as a Large Letter instead.

Sending a thicker pack of papers, a brochure, or a magazine

Printed materials often push thickness beyond 0.5cm. If your item is still flat and within 35.3cm x 25cm and 2.5cm thick, it typically fits the Large Letter format. A Large 1st Class stamp is commonly used when you want the 1st Class service level for this size band.

Case Study: Avoiding a “Size Band” Surprise at the Postbox

Scenario: A sender prepares a document pack for a client—several pages, a return envelope, and a small brochure—placed into a C5 envelope. The length and width look fine, so they assume it’s a standard Letter. However, the contents make the envelope slightly rigid and thicker than 0.5cm.

Outcome: Because thickness is part of the Letter definition, the item no longer qualifies as a Letter. Re-checking the thickness and switching to a Large Letter stamp prevents delays and reduces the chance of surcharges or returns. The lesson is simple: measure thickness as carefully as length and width, especially when sending multi-page packs.

How to Choose the Correct Stamp (Step-by-Step)

1. Measure length and width. Compare your envelope or mailer to the Letter (24cm x 16.5cm) and Large Letter (35.3cm x 25cm) limits.
2. Measure thickness at the thickest point. If it’s over 0.5cm, it won’t qualify as a Letter. If it’s over 2.5cm, it won’t qualify as a Large Letter.
3. Weigh the item. Letters are up to 100g; Large Letters are up to 750g. If you’re close to a limit, re-check after sealing.
4. Pick the service level. Choose 1st Class when you want the 1st Class service level; choose 2nd Class for routine letters where speed is less critical.
5. Apply the stamp correctly. Place the stamp on the top-right of the address side, on a clean, dry surface so it adheres properly.

Packaging Tips That Help Your Mail Travel Well

Keep it flat and machinable when possible

Mail that is flat, evenly filled, and securely sealed is easier to process. Avoid creating a “lumpy” envelope by stacking thick items in one corner. If you must include multiple items, distribute them evenly or consider a more suitable mailer that keeps the profile consistent.

Choose the right envelope size

Using an envelope that is too small can cause bulging and increase thickness beyond the Letter limit. Using an envelope that is too large can lead to bending or creasing. Aim for a snug fit that still allows the contents to lie flat.

Seal securely

Ensure the flap is fully sealed along the entire edge. If you’re sending heavier Large Letters (for example, thick brochures), consider reinforcing the seal so it doesn’t open during handling.

Address clearly

Use a legible, high-contrast address. Keep the address block clear of graphics and avoid placing tape over the address. If you’re using a window envelope, ensure the address sits fully within the window and doesn’t shift.

Letter vs Large Letter: Quick Reference

• Letter: up to 24cm x 16.5cm x 0.5cm, up to 100g.
• Large Letter: up to 35.3cm x 25cm x 2.5cm, up to 750g.

If your item is close to the thickness limit, measure after sealing. Even a small increase in thickness can move an item from Letter to Large Letter.

Frequently Asked Questions (Q&A)