Concrete Calculator

Estimate the concrete bags or bulk cubic yards needed for slabs, patios, walkways, or post hole columns.

Pour Shape Type

Pour Shape

Slab Length

2 ft 10 ft 100 ft

Slab Width

2 ft 10 ft 100 ft

Slab Thickness

Bags Spec

Standard Pre-mix Bag Size

Estimated Concrete Needed (10% Waste Cushion Included)

0 Bags

Volume: 0 cubic yards

How to Estimate Concrete Mix

Whether you are ordering ready-mix concrete by the "yard" or buying premixed bags from a local home improvement store, estimating concrete correctly is essential. Running short means structural joints fail, and ordering too much results in waste disposal fees.

Concrete Bag Yield Factors

Pre-mixed concrete bags are dense. You need a large number of bags to cover even small projects. Here is the volume yield per bag size:

80 lb Bag: Yields **0.60 cubic feet**. It takes 45 bags to make 1 cubic yard.
60 lb Bag: Yields **0.45 cubic feet**. It takes 60 bags to make 1 cubic yard.
40 lb Bag: Yields **0.30 cubic feet**. It takes 90 bags to make 1 cubic yard.

Cubic Yard Formulas

Concrete is ordered by the **Cubic Yard (27 cubic feet)**. To calculate bulk concrete for flat slabs: `Length (ft) × Width (ft) × Thickness (ft) / 27`. For example, a 10x10 slab that is 4 inches (0.33 feet) thick requires `10 × 10 × 0.33 / 27 = 1.22 cubic yards` of concrete.

Frequently Asked Questions

When should I order bulk ready-mix vs. buying bags? +

If your project requires more than **1 cubic yard (roughly 45 bags of 80 lb concrete)**, ordering ready-mix bulk delivery from a mixing truck is highly recommended. Mixing 45+ bags by hand in a wheelbarrow is extremely labor-intensive and makes it hard to pour before the concrete starts setting.

Does cement differ from concrete? +

Yes. Cement is the fine binding powder (the active ingredient). Concrete is the complete mixture of cement, sand, gravel aggregates, and water. Pre-mixed bags contain concrete (aggregate mixed in).