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How much concrete do I need? Slabs, strip footings and post holes, in cubic yards or cubic metres. Enter the yield printed on your bag to count bags. Post sizes are subtracted from post holes.
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Concrete pour · saves on this device as you type
Quick answer Pending
Add length, width and slab thickness
Result pending. Add length, width and slab thickness.
Pours 1
In cubic feet —
Status Pending input Slab plan waiting for measurements Your plan will appear here Your plan will appear here Why this result Every step, with your numbers.
1 Slab: area × thickness Add length, width and slab thickness
2 + Allowance you chose Nothing added yet.
How this concrete calculator works What it calculates Slabs : area of a rectangle, square, circle or L-shape × thickness.Strip footings : length × width × depth × how many.Post holes : π × (diameter ÷ 2)² × concrete depth, minus the post that sits in it, × number of holes.Bags : order volume ÷ the yield on your bag, rounded up (Store Mode).What it does not do It does not choose a thickness, footing size, reinforcement or strength. Those are design and code decisions. It does not assume a bag yield. Yields differ by product and bag size; the label states it. It does not model steps, walls, or anything structural beyond plain volumes. Worked examples A 10 × 10 ft pad, 4 in thick 100 sq ft × (4 ÷ 12) ft = 33.33 cu ft = 1.23 cu yd. One manufacturer’s data sheet lists about 0.60 cu ft per 80 lb bag (Quikrete Concrete Mix 1101 ). 33.33 ÷ 0.60 = 55.6 → 56 bags before any allowance. Ten fence-post holes Hole: 10 in wide, 24 in of concrete. π × 5² × 24 = 1,885 cu in. 4×4 post (3½ in actual): 3.5 × 3.5 × 24 = 294 cu in. Concrete per hole: 1,591 cu in = 0.92 cu ft. Ten holes: 9.21 cu ft ÷ 0.60 cu ft per bag = 15.3 → 16 bags.