Buy too little and you’re back at Bunnings mid-job. Buy too much and you’ve wasted money. This free materials calculator works out how much floor material, wall paint, or wall tile you actually need — including the waste percentage your material type requires. Enter your room dimensions and it does the maths.
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Why waste percentages matter
Cutting materials to fit a room always produces off-cuts you can’t use elsewhere. Different materials need different buffers:
- Straight-lay tile / vinyl plank / laminate: 10%. Standard cuts around walls only.
- Diagonal-lay tile: 15%. Every cut creates two triangles instead of one usable piece.
- Solid timber / engineered timber: 12%. Some boards get culled for defects.
- Mosaic / small-format tiles: 15%. Higher because of the sheet backing and cut lines.
- Paint: 10%. Covers touch-ups and future repairs.
- Carpet: 10%. Roll widths (typically 3.66 m) can force extra buying.
How the paint calculation works
We calculate wall area as perimeter × ceiling height, then subtract doors (assumed 1.9 × 0.85 m) and windows (assumed 1.2 × 1.5 m average). We multiply by the number of coats you’re doing, divide by ~12 m²/L (typical paint coverage per litre), and add 10% for touch-ups.
Rough or unpainted surfaces (fresh plaster, exterior render) can drop coverage to 8 m²/L — buy an extra litre if that’s your situation. Dark colours going over light usually need 3 coats.
Related renovation cost guides
- Flooring Cost Calculator
- Painting Cost Calculator
- Bathroom Renovation Cost Calculator
- Renovation Quote Comparator
- Renovation Timeline Planner
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