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Internal · tiles · adhesive · grout
How many tiles, and how much adhesive and grout?
Tiles with a cutting allowance, adhesive by bed depth and grout by the actual joint volume — not the one-kilo-a-metre guess on the back of the bag.
1
Measure it
Every box has its own unit next to it.
Change the unit beside any box and the number converts. The (i) beside each question says what the box wants and where the figure usually comes from. Anything marked per cent is a percentage of the quantity above it.
2
Check the rates
Rates and assumptions used
These are the figures the calculator works to. Change any of them and the order list updates — your merchant’s pack sizes and your own waste allowances beat the defaults every time.
The figures the calculator works to. Every one can be changed in step 2, and your merchant’s pack sizes and your own waste allowances beat these defaults every time.
Rate
Default
Why
Adhesive
1.5 kg/m²/mm
Per square metre per millimetre of bed depth.
Adhesive bag
20 kg
Grout density
1.6 kg/L
Tiles per box
8 no.
Check the actual box — it varies with size.
Grout bag
5 kg
Primer coverage
10 m²/L
A worked example
With the defaults the page opens on:
How much area to tile? 12 square metres
How long is a tile? 600 millimetres
How wide is a tile? 300 millimetres
How thick is a tile? 9 millimetres
How wide are the joints? 3 millimetres
Spare for cuts 10 per cent
How thick a bed of adhesive? 3 mm — flat wall
Tiles
Tile size: 0.18 m² — 600 × 300 mm
Cutting waste: 10 %
Tiles: 74 no.— area ÷ tile area, +10%
Boxes: 10 boxes — at 8 a box
Trim / edging: 3 × 2.5 m — estimate — count your exposed edges
Adhesive & grout
Adhesive: 54 kg — at 3 mm bed
Adhesive bags: 3 × 20 kg
Grout: 2.6 kg— joint volume × 1.6 kg/L
Grout bags: 1 × 5 kg
Primer: 2 litres
Spacers: 1 × 100 packs
Change any figure above and every line recalculates; the small print under each row is the sum that produced it.
Questions people ask
How many tiles do I need?
Area ÷ tile area × cutting waste. 12 m² in 600 × 300 tiles at 10% needs 74 tiles - about 10 boxes of 8.
How much grout do I need?
Not the one-kilo-a-metre guess on the bag. The calculator works the actual joint volume: ((L + W) ÷ (L × W)) × joint width × tile thickness × 1.6 kg/L. Narrow joints on big tiles use far less than that guess.
How much adhesive?
1.5 kg per square metre per millimetre of bed: 3 mm for a flat wall, 6 mm for a floor, 10 mm for uneven backgrounds or large format tiles, which also need back-buttering.
How much cutting waste?
10% on a square lay, 15% with a diagonal lay or lots of cuts.
Read before you order. These work out quantities, not structural design — spans, lintels, rebar and foundation depths need an engineer and Building Control sign-off. Waste allowances are defaults, not promises: awkward cuts, long runs and bad weather all eat more than 5%. Where a merchant sells whole packs, the figure is rounded up to whole packs.
