Home Improvement
Patio Slab Calculator
Measure the patio, enter slab size, and see how many slabs to buy with waste.
How many patio slabs?
Patio projects fail more often on under-ordering slabs than on the maths being hard. Enter the patio length and width, the slab size, and a waste percentage for cuts and breakages. Rectangles are straightforward; diagonal layouts and circular features need more waste than a grid. Sub-base (Type 1) and sharp sand bedding are volume problems — use concrete calculator thinking for depth × area, or garden soil for loose fills. Falls for drainage, edge restraints and jointing compound sit outside the slab count. Buy from one batch where colour vary, and keep a few spares for future chips. Estimate only — not a landscaper’s survey. Check whether slabs are sold individually or in packs covering a stated m², then reconcile packs with this count. Wet-cut discs and listening to the weather forecast matter more on the day than shaving one slab off the order.
Worked example
A patio 5 m × 3 m = 15 m². Using 600 × 600 mm slabs (0.36 m² each) needs 15 ÷ 0.36 ≈ 41.7 → 42 slabs before waste. At 10% waste, order 46 slabs. Packs of 10 mean five packs (50) with a small spare buffer — usually wiser than four packs and a panic mid-lay.
Limits and assumptions
Assumes a rectangular area and a single slab size. Circles, mix-size patterns and steps need segmented take-offs. Does not design falls or sub-base depth.
Frequently asked questions
How much waste should I add?
About 5–10% for a simple grid; more for diagonals, curves or lots of cuts at walls.
Do I count in slabs or square metres?
Either — convert with slab length × width, then apply waste.
What about joint gaps?
If joints are wide, effective coverage per slab falls — check the manufacturer’s laying guide.
Should sub-base be in this calculator?
No — calculate sub-base volume from area × depth separately.
Mixed slab sizes?
Run each size as its own area segment, then sum packs.