Material estimator

Concrete Calculator

Estimate concrete volume, cubic yards, bag counts, total bag weight, and material cost for slabs, pads, and small pours.

How This Calculator Works

Use this concrete calculator when you need a fast buying number before going to the store or calling for ready-mix. It converts feet and inches into cubic yards, compares common bag sizes, and flags when a pour is large enough to consider delivery.

Formula

Volume = length x width x thickness. Convert thickness from inches to feet, divide cubic feet by 27 for cubic yards, then divide cubic feet by bag yield for bag count.

Assumptions

Default bag yields are 40 lb = 0.30 ft^3, 50 lb = 0.375 ft^3, 60 lb = 0.45 ft^3, and 80 lb = 0.60 ft^3. Add 5-10% overage for uneven base, spillage, and form variation.

Example

A 12 ft by 10 ft slab at 4 inches thick with 10% overage needs about 1.63 cubic yards, or about 98 bags of 60 lb mix / 74 bags of 80 lb mix.

Before You Buy

Use bagged concrete for small pours and compare ready-mix once the estimate passes about one cubic yard.
Measure thickness in several spots if the base is uneven; one extra inch across a slab changes the order quickly.
Keep gravel base, reinforcement, forms, expansion material, and finishing tools outside this material total.

Common Questions

How many bags are in one cubic yard?

One cubic yard is 27 cubic feet. Using common yields, that is about 90 bags of 40 lb, 72 bags of 50 lb, 60 bags of 60 lb, or 45 bags of 80 lb concrete mix.

When should I consider ready-mix delivery?

Once the estimate is around one cubic yard or more, compare bagged cost, hauling weight, and mixing time against local ready-mix and short-load fees.

Should I add waste?

Yes. For most DIY pours, 5-10% is a practical starting point. Irregular forms and rough subgrade may need more.