Yes, working out tile quantities for a bathroom floor is absolutely something a NZ homeowner can do themselves — no trade licence required. With a tape measure, a notepad, and a bit of straightforward maths, you can arrive at a reliable figure that helps you buy the right amount of tile without over-spending or running short mid-job.
Why Getting the Quantity Right Matters
Ordering too few tiles is one of the most common (and frustrating) tiling mistakes. Tiles are often produced in batches, and if you go back for more later, the new batch may have a slightly different shade or texture — even with the same product code. Ordering a little extra upfront is always the smarter move. Conversely, massively over-ordering wastes money, especially with premium tiles.
Step 1 — Measure Your Floor Area
Start by measuring the length and width of your bathroom floor in metres, then multiply them together to get the area in square metres (m²).
Example:
- Room length: 2.4 m
- Room width: 1.8 m
- Area: 2.4 × 1.8 = 4.32 m²
If your bathroom has an irregular shape — for example, an alcove for a toilet or a step-in shower — break the floor into rectangles, calculate each section separately, then add them together.
Deducting Fixed Fixtures
You generally do not deduct the footprint of a toilet, vanity, or bath from your tile area. These fixtures sit on top of the tiles in most installations, and tiling underneath them is standard practice (it also protects the floor if fixtures are ever replaced). Only deduct large, permanent structures like a tiled shower base that is built in before tiling.
Step 2 — Add a Waste Factor
Tiles need to be cut around edges, corners, pipes, and obstacles. Cuts mean offcuts, and offcuts mean waste. You should always add a waste allowance on top of your net floor area.
| Tile Layout / Room Complexity | Recommended Waste Factor |
|---|---|
| Simple square room, straight lay | 10% |
| Diagonal (45°) lay or complex shape | 15–20% |
| Small mosaic tiles or intricate pattern | 15–20% |
| Large format tiles (600 mm+) | 10–15% |
For most standard NZ bathrooms, 10–15% is a safe starting point.
Example continued:
- Net area: 4.32 m²
- Add 15% waste: 4.32 × 1.15 = 4.97 m² → round up to 5.0 m²
Step 3 — Convert to Number of Tiles
Once you know the total area to order, divide it by the area of a single tile.
Tile area = tile length (m) × tile width (m)
For example, a common 300 mm × 300 mm floor tile:
- Tile area = 0.3 × 0.3 = 0.09 m²
- Number of tiles needed = 5.0 ÷ 0.09 = 55.6 → round up to 56 tiles
Many tile suppliers and retailers — including those at Bunnings and Mitre 10 — sell tiles by the box, so check how many tiles are in each box and how many m² a box covers (this is usually printed on the packaging).
Step 4 — Check Grout Joint Width
The grout joint (the gap between tiles) affects how many tiles fit in a given space. Most floor tiles use a 2–5 mm joint. For very large format tiles, joints can be 3–10 mm. Your tile supplier can advise the recommended joint width for the specific tile you've chosen. For most standard calculations, the joint width has a minor effect on the overall tile count, but it's worth confirming before you finalise your order.
Step 5 — Order and Keep Your Receipt
Once you've calculated your quantity, buy all tiles from the same batch number (printed on the box). Keep a couple of spare tiles after the job is done — they're invaluable if a tile cracks years later and the product has been discontinued.
Tile Selection and NZ Bathroom Requirements
For bathroom floors, always choose tiles rated for wet area and slip resistance. In New Zealand, bathroom floors must comply with the NZ Building Code, particularly Clause F2 (Hazardous Materials) relating to slip resistance. Look for tiles with a P3 or R10+ slip rating for wet bathroom floors — your tile supplier should be able to confirm the rating. BRANZ provides useful guidance on wet area construction standards.
When to Call a Professional
Calculating tile quantities is DIY-friendly, but the installation itself involves several considerations:
- Waterproofing is a critical step in NZ bathrooms. Under the Building Code (Clause E3), wet areas must be properly waterproofed. Waterproofing membranes must be correctly applied before tiling — if done incorrectly, you risk serious water damage and potential liability issues when selling your home.
- Building consent is generally not required for straightforward bathroom retiling, but if you're altering the layout, moving plumbing, or doing structural work, check with your local council first. See MBIE Building Performance for Schedule 1 exemption guidance.
- Plumbing work — moving or connecting pipes — is restricted work and must be carried out by a licensed plumber registered with the Plumbers, Gasfitters and Drainlayers Board.
- Electrical work — adding or moving bathroom lighting, fans, or heated towel rails — is restricted work requiring a registered electrician through the Electrical Workers Registration Board.
If you'd prefer to leave the whole job to a professional tiler or quantity surveyor, you can find qualified local tradespeople on tradedirectory.co.nz.
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