Why the stamp on your card matters more than you think

Handwritten correspondence has enjoyed a quiet revival, and it is easy to see why. A card that lands on the doormat, addressed in someone's own hand, carries a warmth that no message on a screen quite matches. But before that card begins its journey, it has to satisfy the rules of the postal system — and those rules are stricter than most of us assume. The stamp you need is not decided by how special the card feels. It is decided by three very ordinary measurements: size, thickness and weight. Get one of them wrong and your carefully written card can arrive with a surcharge to pay, or not arrive at all.

The three size bands you need to know

For anything under 2kg posted within the UK, there are three relevant bands. They are based on the largest dimensions once the item is sealed and ready to go:

• Letter — up to 240mm long, 165mm wide and 5mm thick, weighing no more than 100g. Most C6 and C5 envelopes, DL envelopes and standard A5 cards fall comfortably inside this band.
• Large letter — up to 353mm long, 250mm wide and 25mm thick, up to 750g. This catches unfolded A4 cards, thicker A5 cards, and anything with a bit of bulk to it.
• Small parcel — up to 450mm × 350mm × 160mm, up to 2kg. Anything thicker than 25mm ends up here, whether or not it feels like a parcel to you.

The price gap between bands is not small. A large letter typically costs roughly twice what a standard letter does, and a small parcel more again — from around £3.50 at the lightest end. That is a steep jump for a birthday card with a ribbon on the front, so it is worth knowing which band you are in before you seal the envelope.

Thickness is the trap most people fall into

Five millimetres sounds generous until you actually measure it. A single sheet of card in a paper envelope is usually well under 2mm, but add a fabric bow, a wooden star, a packet of seeds, a few sticky gems or a sheet of stickers and you can sail past the limit without realising. Print your card on heavyweight board and you are halfway there before you start decorating.

There is a simple test. Hold the sealed envelope between finger and thumb and try to push it through a 5mm gap — a slot in a ruler works well, or the edge of a hardback book cover. If it will not pass, treat it as a large letter. Lumpy, rigid or irregular items also cannot go through the sorting machinery, so they may need to be handled separately. This is exactly the kind of thing to ask about at the counter rather than guess at the postbox.

Weighing up the weight bands

Weight is rarely the deciding factor for a single card. A typical C5 card in its envelope weighs somewhere between 15g and 25g, which leaves plenty of room under the 100g letter limit. Weight starts to matter when you enclose something extra: printed photographs, a gift card, a slim booklet, a pressed flower, or several cards sent together to save on postage.

A basic kitchen scale is perfectly adequate. Weigh the finished, sealed envelope, not the card on its own. Remember that the banding is tiered — for large letters and parcels you pay more as you move up through the weight steps toward 750g and 2kg, so a few grams can occasionally tip you into the next price.

Practical habits that save money and hassle

• Buy stamps in booklets rather than one at a time. It is cheaper per stamp, and you always have one to hand when a birthday sneaks up.
• Write the postcode clearly and in capitals on its own line. It is the single most useful thing you can do to get a card delivered promptly.
• Use the full address, including the house number or name. Nicknames and vague directions slow things down.
• Ask at the counter when a card is handmade, thick or oddly shaped. Staff can tell you in seconds whether it needs a larger stamp or a hand-cancelled mark. It is far better than having it returned.
• Post early in December. Christmas deadlines come round faster than anyone expects, and posting a week ahead costs nothing but a little forward planning.
• Keep a small stock of second-class stamps. For cards that are not time-critical, they offer excellent value and the delivery difference is often only a day or two.

A quick word on cards going overseas

International postage works on a different set of bands, usually measured in grams up to 100g, 250g and beyond, with separate rates for Europe and the rest of the world. Sizes still matter, so the same advice applies: measure, weigh, and check before you post. Rates at home and abroad are revised regularly — often in the spring, and sometimes again later in the year — so treat any figure you remember as a guide rather than a guarantee.

The golden rule is simple. Check current pricing by weight and size before posting, and when a card is large, thick or decorated, ask at the counter rather than risk it. A little care at the kitchen table means your handwriting arrives exactly where it was meant to go.