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Calculate cubic yards, bag counts, and order quantities for slabs, footings, columns, stairs, and piers.
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How To Calculate Concrete Volume
The base formula stays the same across shapes: volume in cubic feet, then divide by 27 to get cubic yards.
Quick process
- Measure all dimensions accurately.
- Convert inches to feet when needed.
- Compute cubic feet based on project shape.
- Convert to cubic yards and add waste factor.
Bag yield reference
| Bag Size | Approx. Yield | Typical Use |
|---|---|---|
| 40 lb | 0.30 ft^3 | Small repairs |
| 60 lb | 0.45 ft^3 | Posts and pads |
| 80 lb | 0.60 ft^3 | Most DIY pours |
Frequently Asked Questions
How many 80 lb bags are in one cubic yard?
About 45 bags, because one 80 lb bag yields roughly 0.6 cubic feet and a cubic yard is 27 cubic feet.
Should I add extra concrete?
Yes. Add 5% to 10% for waste, form irregularities, and spill loss. Complex pours may require more.
When should I order ready-mix instead of bags?
For most projects above 1 to 1.5 cubic yards, ready-mix is usually faster, cleaner, and often lower total effort.
What this calculator does
This tool turns your pour dimensions into cubic yards, cubic feet, and bag counts so you can order ready-mix or buy bagged concrete without guessing. It handles slabs, continuous footings, columns, stair runs, and round piers or sonotubes from the same form. Optional price-per-yard input gives you a quick material budget before you call the plant or load the trailer.
What each input means
- Project type: Picks the geometry—slab, footing, column, stairs, or cylinder—so only the fields you need appear.
- Length, width, and thickness (slab): Overall footprint and slab depth in feet and inches. Thickness is the controlling number for yardage on flatwork.
- Footing length, width, and depth: Total run of trench or wall footing in feet, with cross-section width and depth in inches.
- Column width/diameter and height: Square or round pier size and vertical height, plus count when you have multiple posts.
- Stair width, rise, run, and step count: Defines the stair volume from tread and riser geometry across the full flight.
- Cylinder diameter, depth, and hole count: Round pier or tube forms—diameter and depth in inches and feet, multiplied by number of holes.
- Price per cubic yard: Local ready-mix rate for a rough cost line on the estimate (optional).
Using the results on the job
Order ready-mix using the cubic yards figure and add 5–10% overage when grade, forms, or access are uncertain—running short mid-pour is expensive. Bag counts are useful for small pads, post holes, or touch-up; round up to full pallets when the supplier sells by the layer. Compare the order recommendation to your pump or chute plan before the truck arrives, and write the final yardage on the pour ticket so the crew and driver agree on quantity.
For footings and walls, verify trench width matches what you modeled—bell bottoms and keyways add volume fast. Stair pours often need a second person on forms; the calculator gives volume only, not finish labor. On cylinder piers, double-check diameter is outside form size if you are using sonotube labels versus measured ID.