How much concrete do I need?
The search is usually a patio, a pad, or a set of post holes the night before a store run. You want a number you can say out loud at the contractor desk or while loading bags — not a lecture on cement chemistry. Enter the same kinds of dimensions as our main concrete tool. This page is worded for the question form; the math is volume → waste → yards → bags. If you already live in “slab mode,” the slab calculator may feel faster.
+10% so you don't come up short
Estimate only — not a contractor bid. Confirm bag yields and local codes before you pour or order.
When to use
You googled the question literally; you are explaining the buy to a partner who does not want “prism volume” jargon; you need a single landing page before branching into bags vs truck.
When not to
Engineered foundations, colored stamped quotes, or pump-truck logistics. Those need people on site.
Assumptions
Same yields and waste defaults as the concrete calculator. Question-page framing only — not a different formula universe. 80 lb ≈ 0.60, 60 lb ≈ 0.45, 40 lb ≈ 0.30 cu ft.
Worked examples
Example 1
10×20 ft sidewalk, 4 in, 10% waste
→ ≈ 2.47 yd³ ordered — usually a short truck, not 100+ bags
Example 2
Single 18 in diameter × 30 in deep footing hole, 10% waste
→ Small bag count — compare 60 vs 80 lb on the ticket
How it calculates
Measure twice, thickness in inches, then waste. Read yards and bags on the ticket.
- Pick slab, holes, or bags-from-yards.
- Enter dimensions or a known yardage.
- Set waste and bag size; copy the order list.
Same as main concrete page: geometry → cu ft → yd³ → × (1 + waste) → bags.
Common traps
- Square feet is not enough. Without thickness you cannot buy concrete.
- “One yard” is 27 cubic feet, not “a square yard of driveway.”
- Weather window. Knowing the volume does not mean you can finish finishing before it sets.
Next tool
Full shape toolkit → concrete calculator.
Bags only → concrete bag calculator.
FAQ
About 1.23 yd³ at 4 inches before waste; add ~10% unless your base is perfect.
Related
Estimate only — not a contractor bid or engineered takeoff. Confirm bag yields and local codes before you pour or order.