How Many Tiles Do I Need? A Practical Guide to Ordering Tiles (and Allowing for Waste)

Planning a tiling project usually starts with a simple question:

How many tiles should I order?

It sounds straightforward, but there are a few important factors that can affect the final quantity. Tile size, layout patterns, surface preparation and installation methods can all influence how many tiles, bags of adhesive and grout you’ll need.

At Just Tiles NI we help customers with this every day, and one thing we always say is that a little planning goes a long way. This guide explains how to measure correctly, what “wastage” actually means in tiling, and why speaking to your installer early can make the whole process smoother.

Step 1: Measure the Area Correctly

Start by measuring the length and width of the space you want to tile. Multiply the two together to get the square metres (m²). Sometimes, the shape of the room will require you to add together multiple areas. For example, an L shaped room:

If you're tiling walls, the same rule applies. Measure the height and width of each wall and multiply them.

Tiles are produced in manufacturing batches, sometimes called calibre or shade batches. Even with the same product, a later batch may have a slight colour variation.

That’s why it’s always best to order the correct quantity from the same batch the first time.

Step 2: Estimate Tile Wastage

You’ll often hear people say you should allow extra for wastage, but many homeowners aren’t quite sure what that means.

Wastage doesn’t necessarily mean tiles being thrown away. It mostly refers to tiles that must be cut to fit the edges of a room or around obstacles.

For example:

• around walls
• around toilets or sinks
• around door frames
• around pipes
• at corners or awkward angles

When a tile is cut, part of it becomes unusable. Imagine a tile that needs to be cut to fit against a wall. Once it is cut, that piece usually has:

• one factory edge
• one cut edge

The factory edges are perfectly straight and finished, while cut edges are rougher and designed to sit against a wall or under a trim. If you try to use two cut edges in a visible joint, the finish can look uneven. So in many cases the leftover piece from a cut tile cannot be used somewhere else, which is where most wastage occurs. This is completely normal in tiling and happens on every project.

The layout pattern you choose has a big impact on how much cutting is required. Some layouts are very efficient, while others involve much more cutting and planning. Below are typical waste allowances installers work with.

Straight Grid (Stacked Layout)

Tiles are laid in straight rows where all grout joints line up. Waste allowance: around 10%. This is one of the most efficient layouts and usually produces minimal offcuts.

Brick Bond (Offset Pattern)

Each row is offset, similar to brickwork. This pattern is very common for wall tiles, subway tiles and kitchen splashbacks. Waste allowance: around 10–12%. There are more cuts involved compared with a straight layout.

Herringbone Pattern

A herringbone pattern is created by laying rectangular tiles at 45 or 90 degrees to form a zig-zag design. It looks fantastic but involves a lot of cutting along edges. Waste allowance: around 15%. Because of the angled layout, many of the edge cuts cannot be reused elsewhere.

Diagonal Layout

Tiles are laid at a 45° angle across the room. This can make a space feel larger, but it also means nearly every edge tile must be cut. Waste allowance: around 15%

Modular Patterns

Some tile designs combine multiple sizes to create a repeating pattern. These layouts can involve complex cuts and alignment. Waste allowance: around 12–15%

Large Format Tiles

Large tiles can sometimes reduce grout lines and create a modern look, but they may require additional cutting depending on the room shape. Waste levels can vary, but installers still usually recommend 10–12% extra tiles.

 

Step 3: Calculate Adhesive Quantities

Once you know how many tiles you need, the next step is estimating adhesive.

As a general guide, a 20kg bag of tile adhesive covers around 5m².

However, this can change depending on several factors:

• tile size
• trowel size
• surface condition
• installation method

With larger tiles, installers often apply adhesive to both the surface and the back of the tile. This technique is known as back-buttering and helps ensure a strong bond with full coverage. Because of this, large format tiles may require slightly more adhesive than smaller tiles.

 

Rapid-Set vs Slow-Set Adhesive

Installers typically choose adhesive based on the type of project. Rapid-setting adhesive is commonly used for floors, sets quickly and is useful in high traffic areas. Slow-setting adhesive is commonly used for walls, gives more time to adjust tiles and is useful for detailed layouts

 

Step 4: Estimate Grout

Grout fills the joints between tiles and helps lock everything together. A general guide is 5kg of grout for around 4–5m² of tiles.

But coverage depends on:

• tile size
• grout joint width
• tile thickness

Grout is available in many colours, which allows you to blend the grout with the tile for a seamless look, or contrast the grout to highlight the pattern. Tiles that are rectified have very straight edges, allowing for narrower grout joints and a more modern finish.

Step 5: Surface Preparation

Before tiles are installed, the surface underneath must be suitable. Good preparation helps ensure tiles stay securely bonded for years to come. Some surfaces require a primer or bonding agent before adhesive is applied.This helps the adhesive bond properly to smooth or porous surfaces.

If a floor is uneven, installers may apply a self-levelling compound before tiling. This creates a flat, consistent surface and can also reduce how much adhesive is required.

Timber floors can move slightly as the building expands and contracts. Because tiles are rigid, that movement can sometimes transfer into the tiled surface. To manage this, installers often use an uncoupling mat, sometimes called a debonding mat.

 

What Is Debonding?

Debonding simply means separating the tile layer slightly from the surface below.

Instead of the tiles being rigidly attached directly to the subfloor, a special membrane sits between the two layers. This layer allows small movements in the subfloor without transferring all of that movement directly into the tiles.

An uncoupling mat is a thin membrane installed between the floor and the tile adhesive.

It works in two main ways.

1. Movement management

The structure of the mat allows small horizontal movements in the subfloor without transferring them fully to the tiles.

This helps prevent stress building up in the tile layer.

2. Stress distribution

The mat spreads movement and pressure across a wider area instead of concentrating it in one point. This helps protect the tiles and helps prevent cracking over time. Uncoupling systems are commonly used when tiling over wooden floors, newly poured screeds, or heated floors.

A Simple Tile Ordering Checklist

Before placing your order, it’s worth running through this quick checklist.

• Measure the space accurately
• Calculate the square metre coverage
• Add 10% extra tiles (or up to 15% for complex layouts)
• Estimate adhesive quantities
• Estimate grout quantities
• Check whether the surface needs preparation

The Most Important Tip: Speak to Your Installer Early

While these guidelines are useful, every tiling project is slightly different. Room shape, tile size, layout patterns and surface conditions can all influence how much material is required. Because of that, one of the best things you can do is engage your installer early in the process.

An experienced tiler can help you:

• confirm tile quantities
• advise on the best layout for your space
• recommend the right adhesives and grouts
• identify any accessories or preparation needed

This guidance can help avoid delays, unnecessary costs and ordering mistakes.

We are currently compiling a list of Tilers from all over the UK and Ireland. If you would like to be featured then please reach out to us!

Final Thoughts

Ordering tiles isn’t just about measuring the area. Layout patterns, cutting waste, adhesives, grout and surface preparation all play a role in how much material you’ll need. Taking the time to plan properly – and allowing for realistic wastage – will make your tiling project far smoother from start to finish.

And if you're unsure about quantities or materials, the team at Just Tiles NI are always happy to help guide you through the process.

We have compiled this article into an easy 1 page guide to help you:

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