Concrete Patio Calculator

About Concrete Patio Calculator

Concrete Patio Calculator works out the concrete volume for a patio slab, which is the most common bag mix project around a house. A 4 m x 3 m patio at 100 mm thick needs 1.2 m3, or 1.32 m3 with the default 10 percent waste, which comes to about 110 bags of 25 kg mix or 66 bags of 40 kg mix. In imperial, a 12 ft x 10 ft patio at 4 inches is roughly 1.63 cubic yards with waste, or about 74 bags of 80 lb mix. Patios almost always use 100 mm (4 inches) of concrete because they carry foot traffic and furniture rather than vehicles, so extra thickness adds cost without adding useful strength. The volume figure is the deciding factor between methods: under about 1 m3, bags mixed in batches are practical for one or two people over a weekend, while anything over 1.5 m3 is faster and usually cheaper as a ready mix delivery. If the patio will later take a hot tub or a garden room, treat it as a loaded slab and increase the thickness before calculating.

How to use Concrete Patio Calculator

  1. Choose metric or imperial input
  2. Enter length, width, and depth of your slab
  3. See volume and bag count in both metric and imperial instantly

Frequently Asked Questions

How much concrete do I need for a patio?
Multiply patio length by width by slab thickness. A 4 m x 3 m patio at 100 mm needs 1.2 m3, which becomes 1.32 m3 with a 10 percent waste allowance, roughly 110 bags of 25 kg mix. A 12 ft x 10 ft patio at 4 inches needs about 1.63 cubic yards with waste.
How thick does a concrete patio need to be?
One hundred millimetres, or 4 inches, is standard for a patio carrying foot traffic and garden furniture over a compacted sub base. Increase to 150 mm if the patio will support a hot tub, a garden building or a vehicle at any point.
Is it cheaper to mix bags or order ready mix for a patio?
Under about 1 m3 bags usually win on cost and convenience because ready mix suppliers charge a minimum load fee. Over roughly 1.5 m3, ready mix is normally cheaper per cubic metre and avoids a full day of mixing.
Should I add a fall to the patio and does it change the volume?
Yes, a patio needs a slight fall away from the building, usually around 1 in 80, so water runs off. The fall makes one edge marginally thicker than the other, which the standard 10 percent waste allowance comfortably covers.
Can I pour a concrete patio in sections?
Yes, and for a bag mix patio it is often the only realistic approach. Pour in bays separated by formwork, finish each bay fully before moving on, and treat the joints as deliberate control joints rather than accidental cold joints.

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