Find how many bags of concrete mix you need for a slab or footing.
Concrete is bought by volume, so the bag count follows from length times width times thickness, with the thickness converted from inches to feet. A bag is a fixed slice of that volume — the yield printed on the sack, 0.60 cu ft for a standard 80 lb bag — so bags equal volume divided by yield, always rounded up. The waste allowance matters more than people expect: a subgrade dipping half an inch across a 10 by 8 slab is most of an extra bag. Past about one cubic yard, roughly 45 to 50 of the 80 lb bags, hand mixing stops making sense and ready-mix is usually both cheaper and better concrete because it is batched consistently. Running out mid-pour is the one mistake you cannot undo — concrete placed against a face that has begun to set leaves a cold joint and a permanent weak line.
Concrete Bag Count
Volume = length x width x thickness/12, plus waste; bags = volume / bag yield, rounded up; cubic yards = volume / 27
Forty-five. Each yields 0.60 cu ft and a cubic yard is 27 cu ft, which is why a yard of bagged concrete is both expensive and a long afternoon.
4 inches for a patio, shed base or footpath; 5-6 inches with reinforcement where vehicles will park. Footings are deeper and sized to the load and frost line.
Because you cannot buy two thirds of a bag and you cannot pause a pour to fetch more. Over-ordering by one bag is trivial; stopping mid-pour creates a cold joint you live with permanently.