Letter vs Large Letter: the size and weight limits that change your postage
A few millimetres or a few grams can push your mailing into a more expensive format. Here's where the lines are.
Why the format matters
Every postal provider — Royal Mail and the downstream access carriers such as Citipost, Whistl and The Delivery Group — prices post by format first, then by weight. A Letter is the cheapest format, so keeping your mailing inside the Letter limits is often the single biggest saving available.
The Letter limits
Up to 240mm × 165mm, no more than 5mm thick and up to 100g. A DL or C5 envelope with a few folded sheets usually fits.
The Large Letter limits
Up to 353mm × 250mm, no more than 25mm thick and up to 750g. A C4 envelope, or a C5 that's too thick or heavy, becomes a Large Letter.
Watch the thickness
Thickness catches people out: a C5 pack with a thick brochure can go over 5mm even when it's light. Folding, stitching and heavier paper all add bulk.
Our free weight checker shows the thickness and format of your pack before you print.
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