Concrete Calculators

Buying concrete: bags or ready-mix?

Bagged concrete and ready-mix are the same material bought two ways, and the crossover point is about one cubic yard. A cubic yard is 27 cubic feet. That's 45 bags of 80 lb mix, 60 bags of 60 lb, or 90 bags of 40 lb, all of which you would mix one at a time. Below roughly half a yard, bags are simpler and cheaper: no delivery fee, no minimum load, no clock running on a truck. Above a yard, ready-mix wins on effort and usually on price, and suppliers round orders to the nearest quarter yard.

Which calculator fits your job? For a flat pour, start with the Concrete Slab Calculator. It gives cubic yards for the truck and the bag count side by side. Mixing it yourself? The Concrete Bag Calculator works from any rectangular pour. Odd shapes and round footings belong in the Concrete Volume Calculator, and posts and deck footings in the Post Hole Calculator. Building with block instead? The Concrete Block Calculator counts blocks and mortar bags from the wall's area, and the Rebar Calculator lays out the steel grid for a reinforced slab, lap splices included.

Whatever the pour, order a little more than the bare volume. Ready-mix industry guidance is to order about 4–10% extra for spillage, uneven subgrade and forms that spread. Running short mid-pour is the expensive mistake, not a small leftover.