Concrete Calculator

Measure the length, width, and depth (thickness) of the project area. Multiply these three dimensions together to get the volume. For a rectangular slab, use length x width x depth. For a cylinder, use pi x radius squared x height. Always add 5-10% extra material for waste, spillage, and uneven subgrade.

First calculate the total cubic feet required. Then divide by the bag yield: a 40-lb bag covers 0.30 cubic feet, a 60-lb bag covers 0.45 cubic feet, and an 80-lb bag covers 0.60 cubic feet. For example, a 10x10 foot slab 4 inches thick needs about 33.3 cubic feet, about 56 bags of 80-lb concrete mix.

Sidewalks and patios typically require 4 inches of concrete. Driveways and garage floors should be 6 inches thick. Foundation walls are usually 8 inches, and foundations or footings are typically 12 inches thick. Heavier loads and vehicle traffic require thicker slabs.

1 cubic yard equals 27 cubic feet. Ready-mix concrete bought from a truck is usually sold by the cubic yard, while bagged concrete is measured in cubic feet. To convert cubic feet to cubic yards, divide by 27. For example, 81 cubic feet equals 3 cubic yards.

Ready-mix concrete typically costs $120 to $200 per cubic yard delivered, depending on your location, mix type, and delivery distance. Orders below 5-10 yards may incur a short-load fee. Specialty mixes, fiber reinforcement, or accelerated curing may add $10-30 per yard.

Yes, always add a 5-10% waste factor to your calculated volume. This accounts for spillage, uneven subgrade, form irregularities, and over-excavation. For complex shapes like stairs or irregular forms, consider adding 10-15% extra. It's always better to have extra concrete than not enough during a pour.

Bagged concrete is best for small projects under 1 cubic yard, such as setting fence posts, small pads, or repairs. For projects over 1-2 cubic yards, ready-mix delivery is more cost-effective and practical. Mixing more than 40-50 bags by hand is very labor-intensive.