How many cubic feet does an 80 lb bag of concrete cover?

A standard 80 lb bag of premix concrete (Quikrete, Sakrete, etc.) yields approximately 0.60 cubic feet of cured concrete. A 60 lb bag yields about 0.45 cu ft and a 40 lb bag about 0.30 cu ft.

Should I add a waste factor?

Yes. A 5–10% overage is standard for slabs to account for uneven subgrade, spillage, and mixing loss. For post holes, 10–15% is common since the hole bottom is rarely perfectly flat.

When should I order ready-mix instead of bags?

Once your project exceeds roughly 1 cubic yard (27 cubic feet), ready-mix concrete is usually more cost-effective and less labor-intensive than mixing individual bags. The calculator will warn you when you cross that threshold.

Does this account for reinforcement (rebar/mesh)?

No. Rebar and wire mesh displace a small volume of concrete, but the effect is minor for typical home pours. For heavily reinforced pours, reduce the calculated volume by 2–5%.

What depth should I use for a standard patio slab?

Residential patios are typically 4 inches thick. Driveways that carry vehicle weight should be 6 inches. Sidewalks and paths are usually 3–4 inches.

Concrete Bag Calculator

Enter your project dimensions and bag size to find exactly how many bags of concrete mix you need.

Project Dimensions

Shape

Length

Width

Depth / Thickness

Number of sections

Bag Size

Waste / overage added to the bag count: 10% (default 10%)

Results

Enter dimensions and click Calculate.

Summary

This concrete bag calculator takes your project dimensions — slab, column, or footing — and converts them to an exact bag count for 40 lb, 60 lb, or 80 lb premix bags. It also shows total cubic feet and cubic yards so you can decide whether bagged concrete or ready-mix is the right call.

How it works

Select the shape of your project: slab, column, or footing.
Enter each dimension and pick its unit (length and width default to feet, thickness and diameter to inches).
Choose your bag size: 40 lb, 60 lb, or 80 lb.
Optionally add a waste factor (5–15% is typical for most pours).
The calculator shows total cubic feet, cubic yards, and bag count.

Use cases

Estimating bags for a concrete patio or driveway slab.
Planning a fence post footing or deck column.
Calculating concrete for a garden path or stepping stones.
Budgeting material costs before a home improvement project.
Comparing 40 lb vs 60 lb vs 80 lb bag counts for a pour.
Checking whether a small pour fits within rented mixer capacity.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu