Letter Plates Explained: Types, Sizes, Finishes and How to Fit Them

A letter plate is one of the most-used pieces of hardware on any front door, yet most people never give it a thought until an old one wears out, rattles, or starts letting in a draught. Whether you are fitting a brand-new timber door or simply replacing tired hardware, choosing the right letter plate comes down to understanding the types, the sizes, the finishes, and the measurements that matter. This guide walks you through all of it, and sits alongside our wider guide to front door hardware for external timber doors.

Supplied by Trade Door Handles, trusted UK supplier of architectural ironmongery since 1976, with quick nationwide delivery, a letter plate is the metal fitting mounted over the posting slot in a door. It is sometimes written as one word, letterplate, or called a letter box plate, and it does three jobs at once: it frames the cut opening, protects the exposed timber edges, and carries a hinged flap that closes to keep out weather, wind and draughts.

On most doors the letter plate is fixed with two bolts that pass right through the timber, so the visible plate on the outside and any inner flap on the inside are drawn tightly together. Because it is one of the first things a visitor sees, a good quality letter plate is as much a design detail as a practical one. You can see the full choice on our All Letter Plates range.

Fewer of us receive daily post than we once did, but a letter plate is still a defining feature of a front door and it earns its place for several reasons:

• It gives the postman a sealed, weatherproof route for letters and small parcels.
• It finishes the look of a door and ties in with the knocker, knob and other door furniture.
• A worn, draughty or rattling letter plate can be swapped for a sprung, better-sealed unit to cut heat loss.
• On period and restoration projects, the right style keeps a door true to its era.

In short, even if the daily post has slowed, the humble letter plate remains a small piece of hardware that makes a big difference to how a door looks and performs.

There is more variety here than most people expect. The main styles you will come across are:

A sprung letter plate uses an internal spring to snap the flap firmly shut after each delivery. This is the most popular choice on modern doors because the tight closing action helps keep out draughts and driving rain, and it stops the flap flapping in the wind.

A gravity flap letter plate has no spring - the flap simply falls closed under its own weight. Gravity flaps are common on traditional and Victorian-style plates and give a softer, more authentic period action, though they seal slightly less firmly than a sprung design.

A knocker letter plate combines the posting flap and a door knocker in a single fitting. These are a neat, space-saving option on narrower doors, or where you want a coordinated look without drilling for a separate knocker.

A telescopic letter plate is designed for thicker doors. The two halves adjust to the depth of the door and clamp together, sealing the aperture on both faces, and most include integral brush seals to help cut draughts. Fire-rated intumescent versions are also available for flats and apartments, where the material expands under heat to seal the opening and keep a communal fire door compliant. This makes telescopic plates the go-to option for composite and uPVC doors as well as deeper timber ones. Browse the dedicated telescopic letter plates range if your door is thicker than a standard timber slab.

A vertical letter plate is mounted upright rather than across the door. It is a practical answer for narrow doors, glazed doors, or doors with a central muntin where there simply is not room for a wide horizontal plate.

Getting the size right is the single most important step, especially when you are replacing an existing plate.

Two sizes cover the majority of UK doors:

• 10 x 3 inch (roughly 250 x 75mm) - the standard domestic size that suits most homes.
• 12 x 4 inch (roughly 300 x 100mm) - a larger aperture that is a better choice for busy households, flats with communal doors, and businesses that receive a lot of post.

Alongside these you will find a range of intermediate and oversized letter plates, so it always pays to check the exact figures rather than assuming.

If you are swapping an old letter plate for a new one, measure these three things before you order:

1. Overall size - the full height and width of the visible plate.
2. Aperture - the size of the hole cut through the door itself.
3. Fixing centres - the distance between the two bolt holes.

Matching all three means the new plate covers the old marks, lines up with the existing holes, and slots into the cut aperture without any re-cutting or filling.

Fitting a letter plate to a new door is a straightforward job for a competent DIYer or joiner. The basic sequence is:

1. Mark the aperture position centrally and at a comfortable height, then drill and cut the slot to the plate's aperture size.
2. Ease and smooth the cut edges so the flap and any liner sit flush.
3. Offer up the plate, mark the two fixing-centre holes, and drill them through the door.
4. Pass the bolts through from the front, fit the inner flap or backing on the inside, and tighten evenly.
5. Check the flap opens and closes cleanly and that the seal sits square.

Always work slowly on the cut-out - a clean, accurate aperture is what makes the finished letter plate look professional.

These accessories are often confused, so it is worth being clear on what each one does.

An inner flap (also called an internal letter plate) fits on the inside face of the door. It hides the cut edges of the aperture, adds a second barrier against draughts, and gives the inside of the door a tidy, finished look to match the outside.

A letter tidy is an internal cover, frequently sprung, that channels incoming post neatly downwards. It stops letters scattering across the hall floor and protects fingers and pets from the sprung flap. You will find these in our letter tidies collection.

A blanking plate does the opposite job - it seals over an unwanted or disused letterbox aperture, which is handy when post has been moved to an external box or a communal door.

Finish is where you match the letter plate to the rest of your door furniture. A brass letter plate remains the classic period choice, while black and chrome suit more contemporary doors. We stock letter plates and matching inner flaps across a full spread of finishes:

• Brass tones: Polished Brass, Satin Brass, Antique Brass, Aged Brass and Beeswax
• Chrome and nickel: Polished Chrome, Satin Chrome, Satin Nickel and Polished Nickel
• Bronze, pewter and black: Aged Bronze, Matt Bronze, Polished Bronze, Pewter and Black
• Stainless steel: Polished Stainless Steel, with satin stainless covered below for coastal use

As one of the UK's largest stockists we also carry the leading trade brands. If your project is built around a single supplier, you can shop Carlisle Brass letter plates, Frelan Hardware letter plates, Heritage Brass letter plates and From The Anvil letter plates directly.

Salt air is hard on hardware. For coastal or exposed locations, a grade 316 stainless steel letter plate offers the strongest resistance to rust and corrosion and is the sensible long-term choice. Solid brass and good quality plated finishes also hold up well when cleaned regularly. See the Satin Stainless Steel Letter Plates range for marine-grade options.

A common complaint with older doors is a cold draught whistling through the letterbox. A sprung letter plate helps, and many modern plates include an integral brush or flap seal. Where an extra barrier is needed, a separate internal draught excluder or brush kit can be fitted behind the plate to close the gap without spoiling the look of the door.

A general DIY shed will stock a handful of budget letter plates in one or two sizes and finishes. A specialist architectural ironmonger carries the full picture - multiple sizes, sprung and gravity actions, telescopic and vertical options, matching inner flaps and letter tidies, and dozens of finishes that coordinate with the rest of your door furniture. For anything beyond the most basic replacement, or for period and restoration work, buying from a specialist alongside the wider door furniture accessories range means you get a letter plate that fits, seals and matches the rest of your door furniture first time.

Ready to choose? Explore the full range and find the exact size and finish for your door.