Concrete Calculators
Estimate how much concrete to order for slabs, footings, columns and post holes, and convert ready-mix volumes into pre-mixed bag counts.
Concrete Calculator
Volume for slabs, footings, columns and post holes in yd³ and m³.
Open calculatorConcrete Slab Calculator
Area, volume, forms and cost for patio, shed and garage slabs.
Open calculatorConcrete Bag Calculator
Number of 40–80 lb or 20–30 kg pre-mix bags for a volume.
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About these calculators
Concrete is sold by volume (cubic yards in the United States, cubic metres in the UK, Canada and Australia), while smaller jobs are usually done with pre-mixed bags sold by weight. These calculators bridge the two: measure the space, get the volume, then decide whether a ready-mix truck or a stack of bags makes more sense.
Running short partway through a pour causes cold joints and weak spots, so most estimates add a waste allowance of 5–10%. Uneven subgrade, form bulging and spillage all consume extra material.
Related guides
Guide · 7 min read
How to Calculate Concrete Volume
Formulas for slabs, footings and columns, unit conversions and how much extra to order.
Read guideGuide · 7 min read
How Many Bags of Concrete Do I Need?
Turning a volume into bags, post holes with the post in place, and when ready-mix makes more sense.
Read guideGuide · 8 min read
How Many Fence Posts Do I Need?
Counting posts for straight runs, corners and gates, plus rails, pickets and concrete.
Read guideGuide · 6 min read
How Much Extra Material Should You Buy?
Waste allowances by material, what drives them up, and the cost of running short.
Read guide