Free landscaping calculator
Concrete Calculator — yards & bags
For slabs, patios, and pads. Get cubic yards for ready-mix or bag counts for hand mixing, waste included.
Above roughly one cubic yard (about 45 bags), a ready-mix truck usually beats mixing bags by hand.
How much concrete do I need?
Concrete is figured by volume: length × width × thickness (in feet) gives cubic feet; divide by 27 for cubic yards. The calculator adds a 10% waste allowance — slabs are rarely perfectly level ground, and coming up half a bag short with wet concrete on the ground is the worst possible time to drive to the store.
| Bag size | Yield | Bags per yd³ |
|---|---|---|
| 40 lb | 0.30 cu ft | 90 |
| 60 lb | 0.45 cu ft | 60 |
| 80 lb | 0.60 cu ft | 45 |
How thick should a slab be?
Patios, sidewalks, and shed pads do well at 4 inches. Driveways carrying regular vehicles need 5–6 inches, and anything supporting heavy equipment should be engineered. Slabs should sit on 4 inches of compacted gravel, and anything wider than about 10 feet needs control joints so it cracks where you choose instead of where it wants.
Bags or a ready-mix truck?
Mixing bags is practical up to roughly one cubic yard — about 45 eighty-pound bags, which is already a full day with a mixer. Beyond that, a ready-mix truck delivers a consistent batch all at once, which matters because a slab poured in stages can show cold joints. Many suppliers have a 1-yard minimum and charge a short-load fee for small orders.
Frequently asked questions
How many bags of concrete do I need for a 10x10 slab?
A 10 by 10 foot slab at 4 inches thick is about 33 cubic feet of concrete, or 37 cubic feet with a 10 percent waste allowance. That's roughly 61 eighty-pound bags, 82 sixty-pound bags, or 1.4 cubic yards of ready-mix.
How many 80 lb bags of concrete make a yard?
One 80 lb bag yields about 0.60 cubic feet, so a cubic yard (27 cubic feet) takes 45 bags. A 60 lb bag yields 0.45 cubic feet (60 bags per yard) and a 40 lb bag yields 0.30 (90 bags per yard).
How thick should a concrete patio be?
Four inches is standard for patios, walkways, and shed pads on well-compacted gravel. Driveways should be 5 to 6 inches to handle vehicle weight.
When should I order ready-mix instead of bags?
At about one cubic yard and beyond. That volume equals 45 or more 80 lb bags, which is hard to mix and pour before earlier batches start setting. Ready-mix also gives a single consistent batch with no cold joints.