How much concrete do you actually need?
Free concrete calculators for slabs, driveways, footings, post holes, and steps — with exact bag counts, ready-mix yards, and an honest bags-vs-truck cost comparison. No sign-up, no email, nothing leaves your browser.
Slab Calculator
Enter your project size. Results update as you type.
Prices — national-average defaults, edit to your local prices
Defaults are planning averages, not quotes. Your supplier's prices are the real ones — type them in.
Estimates only, for planning — not engineering or financial advice. Verify quantities with your supplier before ordering; bag yields are manufacturer-published averages and ready-mix prices vary by plant and region.
Every calculator
Concrete Calculator
The full slab calculator — any rectangle, any thickness, bags and yards.
Slab Calculator
Slabs with thickness presets for patios, walkways, driveways, and garage floors.
Bag Calculator
Turn any volume into bag counts — or find out what the bags you already have will cover.
Driveway Calculator
Driveway dimensions, thickness presets, and a bags-vs-ready-mix cost showdown.
Footings Calculator
Continuous footings for walls, decks, and additions — by the run.
Post Hole Calculator
Round holes for fence and deck posts — bags per hole and for the whole job.
Steps Calculator
Concrete steps and stoops from riser height, tread depth, and step count.
Concrete Cost Calculator
What will it cost? Ready-mix delivered vs. bags, with delivery and short-load notes.
Bag yield chart — the numbers every calculator here uses
Bag yields are the manufacturers' published figures (Quikrete and Sakrete both rate their mixes this way). One cubic yard is 27 cubic feet.
| Bag size | Yield per bag | Bags per cubic yard | Bags for 1 cu ft |
|---|---|---|---|
| 80 lb | 0.60 cu ft | 45 | 1.7 |
| 60 lb | 0.45 cu ft | 60 | 2.2 |
| 50 lb | 0.375 cu ft | 72 | 2.7 |
| 40 lb | 0.30 cu ft | 90 | 3.3 |
Full chart with worked examples: How many bags of concrete do you need?
Guides
How Many Bags of Concrete?
The yield chart, the math, and worked examples for common jobs.
Concrete PSI Guide
Which strength mix for walkways, driveways, garages — and when you need air-entrainment.
Slab Thickness Guide
How thick for each job, plus base and reinforcement notes that matter more than thickness.
Frequently asked questions
How much concrete do I need for a 10×10 slab?
At the standard 4 inches thick, a 10 × 10 ft slab needs 33.33 cu ft of concrete, which is 1.23 cu yd. In bags, that is 56 bags of 80 lb mix exactly — order 62 bags with the usual 10% waste allowance, or 1.36 cu yd if a ready-mix truck delivers it.
How many bags of concrete are in a cubic yard?
It depends on the bag size: 45 bags of 80 lb, 60 bags of 60 lb, 72 bags of 50 lb, or 90 bags of 40 lb make one cubic yard (27 cu ft), using the manufacturers' published yields.
How thick should my concrete slab be?
Four inches is the standard for patios, walkways, and shed floors. Driveways that carry cars do better at 5 inches, and 6 inches for heavy trucks, RVs, or poor soil. A well-compacted gravel base matters as much as the thickness — see the slab thickness guide.
Is it cheaper to mix bags or order ready-mix?
Bags usually win on price for small jobs under about half a cubic yard. Around 1 cubic yard — 45 or more 80 lb bags — the labor of mixing catches up with the savings and a ready-mix truck usually makes more sense, even with delivery and possible short-load fees on small orders. The calculators above compare both with your local prices.
Why does the calculator add 10% extra?
Forms are never perfectly level, the ground is never perfectly flat, and some concrete always spills or sticks to the mixer. Ten percent is the standard allowance pros order by. Running short mid-pour is the one mistake you cannot fix — a truck cannot send back a shortage, and a cold joint weakens the slab.