Material estimator

Concrete Bag Calculator

Calculate how many 40, 50, 60, or 80 lb bags of concrete you need for a slab, pad, or small pour.

How This Calculator Works

This concrete bag calculator focuses on the store run: how many bags to buy, what they weigh, and what the pile should cost before delivery fees or tools.

Formula

Bags needed = concrete volume in cubic feet / selected bag yield, rounded up to the next whole bag.

Assumptions

Bag yield varies by product and water content, so check the label. The calculator uses standard planning yields and rounds up because partial bags are not useful on site.

Example

For a 10 ft by 10 ft pad at 4 inches thick with 10% overage, you need about 36.7 ft^3 of concrete, or 62 bags of 80 lb mix.

Before You Buy

Check the yield printed on the exact bag you plan to buy; 80 lb bags are commonly estimated at 0.60 cubic feet, but products vary.
High bag counts create hauling and mixing problems, not just material cost. Compare delivery, rental mixer, and short-load fees.
Round up before shopping. Running out during a pour is usually more expensive than returning an extra bag.

Common Questions

Why does bag weight not equal volume?

Concrete bags are sold by weight, but your project needs volume. Use the yield printed on the bag whenever it differs from the planning defaults.

Can I mix dozens of bags by hand?

You can, but it becomes slow and inconsistent. Large bag counts are a signal to compare rental mixers or ready-mix delivery.

Does this include reinforcement?

No. Rebar, mesh, gravel base, forms, and expansion joints are separate materials.