Wall Tile Calculator

Calculating Wall Tiles: The Complete Guide

Wall tiling is one of the most transformative home improvements you can make. A well-tiled kitchen splashback or bathroom wall is both practical and beautiful, protecting the wall from moisture damage while creating a surface that is easy to clean and maintain for decades. However, calculating wall tiles accurately requires a slightly different approach compared to floor tiles, because walls have openings — windows, doors, niches, and fixtures — that must be subtracted from the total area.

The basic formula for wall tiles is: (wall width × tiling height) − deductions = net area to tile. Divide that net area by the area of one tile (including grout gap) to get the number of tiles needed. Then add your wastage percentage — typically 10% for walls with few obstacles, or up to 15% for walls with many cuts around windows, pipes, and alcoves.

Wall Preparation Before Tiling

Proper wall preparation is essential for a successful tiling job. Tiles are only as good as the surface they are fixed to. The most common wall substrates in UK homes are:

Plasterboard (Drywall)

Standard 12.5mm plasterboard is suitable for light wall tiles in dry areas. For heavy tiles (natural stone, large porcelain) or wet areas, use 15mm moisture-resistant plasterboard (often called green board or Knauf Aquapanel). Seal the surface with a PVA primer diluted 1:4 with water, or use a dedicated tile primer such as BAL Prime APD. In shower areas, apply a tanking membrane over the plasterboard before tiling.

Existing Tiles

You can tile over existing wall tiles if they are firmly bonded and the wall is flat. Sand the old tile surface with 80-grit sandpaper and apply a bonding agent (BAL Bond SBR or similar). However, the combined weight of two layers of tiles may be too much for some plasterboard walls — check the wall can support the load. If in doubt, remove the old tiles first.

Plastered Walls

New plaster must cure for at least four weeks before tiling. Seal with diluted PVA (1:5 ratio). Old plaster should be checked for hollows by tapping with your knuckles — a hollow sound indicates the plaster has blown and must be hacked off and replaced before tiling. Never tile onto blown plaster; the tiles will eventually fall off.

Waterproofing Wet Areas

UK Building Regulations (Approved Document C) require adequate moisture protection in wet areas. For tiling purposes, this means waterproofing (also called tanking) the walls in and around showers, over baths, and in wet rooms. Common waterproofing products used in the UK include:

• BAL Tank-it: A two-coat liquid tanking system that creates a flexible waterproof membrane. Apply with a brush or roller.
• Mapei Mapelastic AquaDefense: A ready-to-use liquid membrane. Quick drying — ready to tile in 30–50 minutes.
• Laticrete Hydro Ban: A thin, load-bearing waterproof membrane popular with professional tilers.
• Sheet membranes: Products like Schluter DITRA-25 provide both waterproofing and uncoupling in one layer. More expensive but extremely reliable.

The waterproofing must extend at least 150mm beyond the wet zone (e.g., beyond the edges of a shower tray). In a wet room where the entire floor is the shower, the whole floor and all walls to at least 1.8m height must be tanked. Joints between the floor and walls should be sealed with a flexible waterproof tape bedded into the membrane.

Splashback Heights: Standard UK Measurements

When tiling walls in kitchens and bathrooms, the height of the tiling varies depending on the area and its purpose. Here are the common heights used in UK homes:

Handling Deductions: Windows and Doors

Accurately subtracting windows and doors from your wall area is critical. Here is how to handle the most common deductions:

Windows

Measure the window frame from outside edge to outside edge, both width and height. This gives you the deduction area. However, if you plan to tile the window reveal (the sides, top, and bottom of the window recess within the wall), you need to add that area back in. A typical window reveal in a UK home (with 100mm wall thickness) adds roughly 0.2–0.4m² depending on the window size.

Doors

A standard UK internal door is 762mm wide and 1981mm tall (the "2’6"" or "6’6"" size). With the frame, the opening is approximately 810mm × 2050mm, or 1.66m². For bathroom doors, some are narrower at 686mm. Always measure the actual frame opening rather than assuming a standard size.

Bathroom Fittings

Generally, do not deduct the area behind a bath, toilet cistern, or vanity unit if these fittings will be removed or replaced in the future. Tile the full wall so that replacements are easier later. The only exception is a built-in niche or recessed shelf that you specifically want left un-tiled.

Popular UK Wall Tile Styles

The most enduring wall tile trend in the UK remains the metro tile (also called subway tile). Available in 200×100mm, 150×75mm, and 250×200mm sizes, metro tiles are stocked by every major UK retailer. Their rectangular shape works equally well in a traditional brick-bond layout or a modern stacked (grid) pattern. Gloss white metro tiles from Wickes or B&Q cost from just £12/m², making them one of the most affordable wall tile options.

For a more contemporary look, large-format wall tiles in 300×600mm or even 600×600mm create a sleek, minimal aesthetic with fewer grout lines. These are particularly popular in walk-in showers and feature walls. However, large wall tiles require a perfectly flat substrate and are heavier, so they need a stronger adhesive (typically a rapid-set S1 or S2 class) and may require mechanical fixing on tall walls.

Frequently Asked Questions