Handles & Hinges • AI Guides

How to Measure Your UPVC Letterbox

Handles & Hinges UPVC Maintenance Ltd is a UK specialist in UPVC door and window parts. Follow these quick steps to record the three sizes you need to order the correct replacement letterbox (letterplate).

Tip: Work with the door open and support the panel while removing fixings. Keep all screws safe for refitting.

Step-by-step

  1. Remove the letterbox
    Open the door. On the inside flap, remove the fixing screws (usually four). Separate the inner and outer halves and slide the letterbox out of the aperture.
    Remove the internal screws to release the letterbox halves
    Remove the internal screws to release the inner and outer halves.
  2. Measure size A — aperture height
    Measure the visible height of the door cut-out (slot) in millimetres.
    Diagram showing letterbox aperture height (A) measurement
    A = aperture height.
  3. Measure size B — aperture width
    Measure the visible width of the door cut-out in millimetres.
    Diagram showing letterbox aperture width (B) measurement
    B = aperture width.
  4. Measure size C — door thickness / sleeve depth
    Measure the thickness of the door where the letterbox sits (or the depth of the sleeve/tunnel). This selects the correct depth setting.
    Diagram showing sleeve depth (C) measurement inside the letterbox aperture
    C = door thickness / sleeve depth (choose matching depth on the product page).

Panel vs Midrail (quick explainer)

A panel door has a letterbox cut through the infill panel. A midrail door has a horizontal rail the letterbox usually sits in. Knowing this helps you choose the correct product family and depth.

Examples of midrail doors vs panel doors with letterboxes
Midrail doors place the letterbox in the rail; panel doors cut through the panel.

Quick reference

Size What it is Why it matters
A Aperture height (slot height) Must match product’s aperture spec
B Aperture width (slot width) Ensures flap clears and covers the opening
C Door thickness / sleeve depth Selects correct tunnel depth / spacers
Browse UPVC Letterboxes Letterbox Springs & Parts

FAQ

Do “10 inch” letterboxes measure 10 inches? Not exactly — sizes are metric. Always use A, B and C measurements from your door.

My flap rattles or sticks open — do I need a new box? Often a spring kit fixes it. If the body is cracked or the brushes are worn flat, replace the whole unit.

What depth should I choose? Match C (door thickness). Many models have adjustable sleeves or spacer sets to suit common depths.