What is the 10% waste factor?

Concrete poured into forms always has slight losses due to spillage, uneven sub-base, and overfill. A 10% buffer is the industry-standard minimum for DIY projects. For complex shapes or rough ground, consider adding 15%.

Which pre-mix bag size should I buy?

80 lb bags give you the most concrete per bag and the best value if you can handle the weight. 60 lb bags are the most common for homeowners. 40 lb bags suit small repairs or situations where carrying heavy bags is difficult.

When should I order ready-mix instead of bags?

If your project exceeds 1 cubic yard (about 45 × 80 lb bags), ordering a ready-mix truck is usually cheaper and less labor-intensive. Below 1 cubic yard, pre-mix bags are typically more economical.

How many cubic feet are in one bag of concrete?

An 80 lb bag yields about 0.60 cubic feet. A 60 lb bag yields about 0.45 cubic feet. A 40 lb bag yields about 0.30 cubic feet. These values are averages — check your specific bag label for the exact yield.

Does this calculator handle circular shapes?

Yes. Select "Circular Footing" for flat discs or "Column" for upright cylinders. Both use the formula π × r² × height to determine volume.

Concrete Calculator

Name: Concrete Calculator
Availability: InStock
Author: Nham Vu

Enter your slab, footing, or column dimensions to instantly calculate the cubic yards, cubic feet, and number of pre-mix bags required.

Dimensions

Shape

Length (ft)

Width (ft)

Thickness (in)

Enter thickness in inches. Common values: 4 in (patio), 6 in (driveway).

Pre-mix Bag Size

Number of identical sections

Use this for multiple footings or columns of the same size.

Enter dimensions on the left to calculate concrete volume.

Bags Needed (with 10% buffer)

60 lb bags

Cubic Feet

0.00

exact

Cubic Yards

0.00

exact

Cubic Meters

0.00

exact

Calculation Breakdown

Shape	—
Sections	—
Volume per section	—
Total volume	—
Volume + 10% waste	—
Bag yield	—
Bags needed	—

Summary

Enter your slab, footing, or column dimensions to instantly calculate the cubic yards, cubic feet, and number of pre-mix bags required.

How it works

Select the shape: slab, rectangular footing, circular footing, or column.
Enter the dimensions (length, width, thickness, diameter, or height) in feet and inches.
Choose the pre-mix bag size: 40 lb, 60 lb, or 80 lb.
Click Calculate to see the volume in cubic feet and cubic yards.
The result shows the exact bag count plus a 10% waste buffer recommendation.
Use the Reset button to start a new calculation.

Use cases

Estimating concrete bags for a backyard patio or driveway slab.
Planning material purchases for fence post footings.
Sizing concrete volume for a sonotube column or pier.
Checking concrete quantities before ordering a ready-mix truck.
Budgeting material costs for a DIY home-improvement project.
Verifying a contractor's concrete estimate.
Teaching students or apprentices how concrete volume is calculated.
Planning multiple pour sections and comparing shape options.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu