How Many Bags of Concrete Do I Need?
Calculate cubic yards and pre-mixed bags needed for slabs, footings, columns, or steps. Supports 40 lb, 60 lb, and 80 lb bags.
Project Type
How to Calculate Concrete Needed
To calculate concrete volume, multiply length × width × depth (all in feet) to get cubic feet. Divide by 27 to convert to cubic yards. For bags, divide cubic feet by the bag volume (0.45 cu ft for 60 lb bags).
For projects under 1 cubic yard, pre-mixed bags are the most practical option. For larger projects, ordering ready-mix concrete from a supplier is significantly cheaper per yard.
Concrete Bag Sizes and Coverage
| Bag Size | Weight | Coverage at 4" depth |
|---|---|---|
| Small bag | 40 lb | ~0.30 cu ft |
| Standard bag | 60 lb | ~0.45 cu ft |
| Large bag | 80 lb | ~0.60 cu ft |
For large pours (over 1 cubic yard), ordering ready-mix concrete by the yard is more cost-effective than bags. One cubic yard = 27 cubic feet = about 45 bags of 80-lb concrete. Ready-mix concrete costs $125–$175 per cubic yard delivered, vs. $4–$6 per bag ($180–$270 per yard equivalent). Minimum delivery quantities vary by supplier — most have a 1 yard minimum, some charge extra for partial loads.
When to Use Bagged vs. Ready-Mix Concrete
Bagged concrete is ideal for small projects: fence posts, mailbox bases, stepping stones, small slabs under 50 sq ft, and repair work. Ready-mix is better for larger slabs, driveways, patios over 100 sq ft, and any pour requiring consistent batch-to-batch color. Ready-mix also lets you pour larger areas continuously — multiple batches of bagged concrete mixed at different times can show slight color and consistency variations in the finished slab.