Is there a standard letter box size? No. Letter boxes are sold as “10 inch” or “12 inch”, but those are only rough names. What matters is the screw centres, the hole in the door and the door thickness.
In our range, 12 inch letter boxes need a hole from 256mm to 278mm wide and have screw centres from 270mm to 292mm. Our 10 inch letter box needs a 223mm wide hole with 236mm screw centres.
This guide shows you how to measure your old letter box in a few minutes, compares the real sizes of the letter boxes we stock, and helps you find one that fits your door without drilling new holes.
How to Measure a Letter Box
- AScrew centres. From inside, measure between the centres of the two fixing bolts or screws. If the new letter box matches, you can reuse the same holes.
- BCHole in the door. Take the old letter box off and measure the width (B) and height (C) of the hole. The new sleeve must fit through it.
- DDoor thickness. Measure the door from the outside face to the inside face, away from any panel moulding. It must fall within the range on the product.
- Plate size. Measure the old outside plate. The new plate should be at least as big, so it covers any old marks.
Tip: measure in millimetres, and measure twice. A few millimetres decides whether a letter box fits the existing holes.
Find a Letter Box That Fits
Enter your measurements and we’ll show the letter boxes in our range that fit the hole and your door thickness, and whether they line up with your existing screw holes.
Letter Box Sizes in Our Range
Real measurements from the letter boxes we stock, sorted by screw centres. Always check the product page before ordering.
| Letter box | Hole in door (B × C) | Screw centres (A) | Door thickness (D) |
|---|---|---|---|
| Yale Welseal 10 Inch Letterbox | 223 × 44mm | 236mm | 18–38mm or 38–78mm |
| Avocet Affinity 12 Inch Heavy Duty | 264 × 50mm | 270mm | 38–78mm |
| Avocet Affinity Ultra 12 Inch Stainless Steel | 262 × 43mm | 270mm | 40–80mm |
| ERA 12 Inch Letterbox Set | 264 × 48mm | 270mm | 20–40mm or 40–80mm |
| Fab & Fix 12" Letterbox Set | 262 × 45mm | 270mm | 20–40mm or 40–80mm |
| GreenteQ Omega New 12 Inch V2 | 259 × 48mm | 270mm | 40–80mm |
| Ultion Sweet 12" Round Edge | 262 × 46mm | 270mm | 40–70mm |
| Ultion Sweet 12" Square Edge | 262 × 46mm | 270mm | 40–70mm |
| Trojan Unicorn 12 Inch Heavy Duty | 260 × 47mm | 273mm | 20–40mm or 38–76mm |
| GreenteQ Coastline 12 Inch Stainless Steel | 256 × 52mm | 275mm | 42–80mm |
| GreenteQ Omega 12 Inch Heavy Duty | 256 × 45mm | 275mm | 40–80mm |
| Yale Welseal 12 Inch Letterbox | 262 × 44mm | 275mm | 18–38mm or 38–78mm |
| Mila ProStyle 12 Inch Heavy Duty | 264 × 46mm | 276mm | 18–38mm or 38–78mm |
| Yale Postmaster 12 Inch Aluminium | 258 × 40mm | 277mm | 40–80mm |
| Fab & Fix 12 Inch Heavy Duty | 278 × 60mm | 290mm | 42–80mm |
| Fab & Fix Heritage 12 Inch Heavy Duty | 275 × 60mm | 290mm | 42–80mm |
| Yale Slim Master 12 Inch | 269 × 38mm | 292mm | 36–70mm |
Notice the spread: every letter box above is sold as 12 inch apart from the Yale Welseal 10 inch, yet the screw centres range from 270mm to 292mm. That is why the measurement matters more than the name.
10 Inch or 12 Inch?
10 inch letter boxes
Smaller, usually on older uPVC doors. In our range: a 223mm wide hole and 236mm screw centres. Shop 10 inch letter boxes
12 inch letter boxes
The most common size today on uPVC, composite and timber doors, with the widest choice of styles and finishes. Shop 12 inch letter boxes
Internal covers
Fit over the inside of the opening to stop draughts. They have their own screw centres, so measure the inside too. Shop letter box covers
If Your Measurements Don’t Match
Screw centres are different
You can still fit it: drill new fixing holes and choose a plate big enough to cover the old ones.
The hole is too small
The hole will need enlarging to suit the new sleeve. Mark it carefully and cut slowly. uPVC and composite doors can have reinforcement inside.
The hole is much bigger
Choose a letter box whose outside plate fully covers the hole, or send us a photo and we’ll suggest one.
Common Mistakes
- Ordering by “12 inch” alone
- Measuring the outside plate instead of the screw centres
- Forgetting the door thickness
- Measuring in inches and rounding
- Not checking the inside cover
Frequently Asked Questions
Is there a standard letter box size in the UK?
No. There is no single standard size. Most replacement letter boxes are sold as 10 inch or 12 inch, but the hole they need and the screw centres vary between brands. In our range, 12 inch letter boxes need a hole from 256mm to 278mm wide and have screw centres from 270mm to 292mm.
What size is a 12 inch letter box?
“12 inch” describes the overall size of the plate, not an exact measurement. The 12 inch letter boxes in our range need a hole between 256mm and 278mm wide and 38mm to 60mm high. Check the screw centres and hole size on the product page before you order.
What size is a 10 inch letter box?
Smaller and usually found on older uPVC doors. The Yale Welseal 10 inch in our range needs a 223mm × 44mm hole and has 236mm screw centres. If your hole is wider than that, you probably need a 12 inch letter box.
Can I replace a 10 inch letter box with a 12 inch one?
Often, yes. You will need to enlarge the hole in the door to suit the new sleeve and drill new fixing holes, and the larger plate will cover the old marks. On composite and uPVC doors, cut carefully: there may be reinforcement inside the door.
Can I fit a new letter box without drilling new holes?
Yes, if the new letter box has the same screw centres as your old one and its sleeve fits through the existing hole. Use the finder above to see which ones match.
How high should a letter box be from the ground?
The standard BS EN 13724 recommends that the letter box opening is between 700mm and 1700mm from the floor. In England and Wales this is guidance rather than a legal requirement at the moment. In Scotland it is included in the building standards from April 2026. It mainly matters when fitting a new door or cutting a new opening.
Will a letter box fit a composite door?
Most of our letter boxes are made for uPVC, composite and timber doors. Composite doors are often thicker, so check your door thickness falls within the range on the product page.
Can I stop the draught without changing the letter box?
Often, yes. An internal letter box cover or brush draught excluder fits over the inside of the opening. Check its size and screw centres against the inside of your door.
Can I fit any letter box to a fire door?
No. Only fit a letter plate that is certified for use on fire doors, and check with the door manufacturer. If you are unsure, ask us before ordering.
Browse all letter boxes: 12 inch letter boxes, 10 inch letter boxes, letter box covers and post box accessories.
Send us a photo of your letter box with a tape measure across it, and the measurements above, and we’ll match it for you.
Monday to Friday, 8:30–12:30 and 13:00–15:30