Concrete Slab, Footing and Column Calculator
Estimate concrete for slabs, footings, pads, and columns; compare ready-mix with 40, 50, 60, and 80 lb bags.
How to use the concrete calculator
- Measure the actual project. Break irregular work into separate sections and record finished dimensions consistently.
- Enter the core measurements. The quick view focuses on project geometry; add or subtract sections where the calculator supports multiple areas.
- Review purchasing assumptions. Open Advanced inputs to replace example prices, waste, coverage, density, pack size, minimum order, or delivery assumptions with current project information.
- Calculate and verify. Review the formula, limitations, whole-unit rounding, product instructions, and supplier requirements before purchasing.
Key inputs covered: Waste allowance, Ready-mix example price, Supplier order increment, Minimum billed load, Delivery / short-load fee, 40 lb bag yield, 40 lb bag example price, 50 lb bag yield, 50 lb bag example price, 60 lb bag yield, and additional project-specific assumptions.
Result coverage: The concrete calculator reports 8 separate quantities so the primary estimate and its supporting purchase or planning values can be checked together.
Calculate concrete yards and bags for common pours
Use separate sections for a slab, footing, post hole, column, curb, stair, or hollow tube. The result combines the sections, adds your waste allowance, and compares ready-mix volume with common bag sizes.
Concrete slabs and footings
Enter finished dimensions and thickness for each section. Concrete volume is calculated in cubic feet and converted to cubic yards using 27 cubic feet per cubic yard.
Post holes, columns, and concrete bags
Round sections use diameter and height. Bag counts use editable product yields, so match the yield to the exact mix and bag weight you plan to buy.
Concrete ordering conversions
The calculator converts cubic feet to cubic yards and rounds bag quantities up using the editable yield for each bag size.
| Quantity | Planning conversion |
|---|---|
| 1 cubic yard | 27 ft³ |
| 40 lb bag default | 0.300 ft³ yield |
| 50 lb bag default | 0.375 ft³ yield |
| 60 lb bag default | 0.450 ft³ yield |
| 80 lb bag default | 0.600 ft³ yield |
Planning note: The bag yields below are starting values used by this calculator. Confirm the yield printed on the selected product and supplier ordering rules. See QUIKRETE quantity guidance.
How the estimate works
Add each section volume, multiply by the waste factor, then divide cubic feet by 27. Bag counts round up; ready-mix follows the entered minimum and increment.
The default 20 ft × 12 ft × 4 in slab requires about 3.26 yd³ including 10% waste.
Assumptions, rounding, and limitations
Dimensions are treated as finished measurements. Only deductions and allowances entered above are included. Decimal measurements display to two places; purchase quantities round up when a whole container or piece is required.
- Bag yields and prices are editable examples, not sourced regional averages.
- Footing and reinforcement design must follow plans, soil conditions, and local code.
- Confirm minimum loads, delivery, and short-load charges with the supplier.
Sources and review
These references support unit conversions and selected planning assumptions. Product instructions and local requirements control the actual project.
Last reviewed: 2026-10-09
Editorial process
BuildPlanCalc publishes the formula, editable assumptions, limitations, and supporting references so the estimate can be checked rather than treated as a black box. See the calculation and review methodology, or report a correction.
Frequently asked questions
Are the results exact?
No. Results are planning estimates based on the dimensions and assumptions entered. Confirm product coverage, site conditions, and ordering rules with the supplier.
Does this design reinforcement?
No. It only estimates concrete volume and cost. A qualified professional must specify reinforcement and structural dimensions.
How many concrete bags are in a cubic yard?
The count depends on the bag's stated yield. One cubic yard is 27 cubic feet; divide 27 by the product yield and round up for a planning count.