Concrete Bags Calculator
How many bags of concrete mix for a small slab? Pick the 40, 60 or 80-lb bag, enter the slab size, and get the bag count and cost — plus when ready-mix becomes cheaper.
Bagged concrete for 5.9 cu ft
10 80-lb bags — 0.22 cu yd · 0.17 cu m
$55 — estimated bag cost at $5.50 per bag
Exact volume is 5.3 cu ft (0.15 cu m); with 10% waste you need 5.9 cu ft. One 80-lb bag yields about 0.6 cu ft of mixed concrete. Bagged mix makes sense up to roughly 1–2 cu yd (about 45–90 eighty-pound bags) — beyond that, ready-mix delivered by truck is cheaper and far less work.
Estimate. Bag yields are the manufacturer's figures; check the bag label and the current shelf price. Each 80-lb bag needs about 1 gallon of water.
Formula used: Volume = length × width × (thickness ÷ 12) cu ft, × (1 + waste%). Bags = volume ÷ yield per bag, rounded up.
How this estimate works: Bagged concrete is sold by weight, but a slab needs a volume, so the tool converts the slab to cubic feet and divides by the yield printed on the bag — about 0.60 cu ft for an 80-lb bag, 0.45 for a 60-lb bag and 0.33 for a 40-lb bag. The waste allowance covers spillage and forms that run a little deep.
How the concrete bags calculator works
Bagged concrete is sold by weight, but a slab needs a volume, so the tool converts the slab to cubic feet and divides by the yield printed on the bag — about 0.60 cu ft for an 80-lb bag, 0.45 for a 60-lb bag and 0.33 for a 40-lb bag. The waste allowance covers spillage and forms that run a little deep. Bagged mix makes sense up to roughly 1–2 cu yd; beyond that, ready-mix delivered by truck is cheaper and far less work. Bag yields are the manufacturer's figures — check the bag label.
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