Concrete Calculator
Estimate concrete in cubic yards, cubic feet or cubic meters for slabs, footings, columns and post holes. Add sections to one pour, then use a product’s bag yield or your supplier’s price to prepare a material estimate.
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How to Calculate Yards of Concrete
Measure the space that concrete will fill. For a rectangular slab, multiply length, width and thickness in compatible units. One cubic yard contains 27 cubic feet.
Concrete yardage = length (ft) × width (ft) × thickness (in) ÷ 324
Example: a 10 × 12 ft slab at 4 in thick needs 40 ft³ = 1.4815 yd³ before allowance. Choosing a 10% extra allowance changes the order estimate to 44 ft³ = 1.6296 yd³. Both thickness and allowance are example inputs.
Square feet still need a thickness
Use the concrete slab calculator with Known area + thickness when you already know the square footage. Measure concrete thickness separately from the base. Split changes in thickness or non-overlapping shapes into separate sections; do not count the same space twice.
| Concrete thickness | Cubic feet | Cubic yards |
|---|---|---|
| 4 in | 33.3333 | 1.2346 |
| 5 in | 41.6667 | 1.5432 |
| 6 in | 50 | 1.8519 |
| 8 in | 66.6667 | 2.4691 |
These are volume examples, not recommended slab thicknesses. Use the dimensions required for your project.
Footings, Columns and Post Holes
A rectangular footing uses length × width × depth. The cylinder concrete calculator mode uses π × (diameter ÷ 2)² × height. Convert all dimensions to the same unit before multiplying.
| Shape | Measurements | Net concrete |
|---|---|---|
| Footing | 20 ft long × 12 in wide × 12 in deep | 20 ft³ |
| Solid column | 12 in diameter × 36 in high | 2.3562 ft³ |
| Post hole | 12 in hole, 36 in deep; 4 in round post embedded 30 in | 2.1380 ft³ |
For a post hole, subtract only the post volume inside the concrete. Enter actual post dimensions and its embedded length, not its full above-ground height. A rectangular post must fit inside the round hole; the tool checks its diagonal against the hole diameter.
For a hollow tube or ring, subtract the inner cylinder from the outer one: π × (outer diameter² − inner diameter²) × height ÷ 4. Use the concrete’s outside diameter, not the outside of a cardboard form. The inner diameter must be smaller than the outer diameter.
These modes estimate material from given dimensions. They do not determine foundation size, embedment, soil capacity or reinforcement.
How Many Bags of Concrete Do I Need?
The concrete bag calculator divides the order volume by the product’s mixed-concrete yield per bag, then rounds up once. Add all sections and any selected allowance before rounding.
Whole bags = round up (total concrete volume ÷ yield per bag)
| Package | Yield per bag | Bags for 1 yd³ |
|---|---|---|
| 40 lb | 0.30 ft³ | 90 |
| 60 lb | 0.45 ft³ | 60 |
| 80 lb | 0.60 ft³ | 45 |
Source: Sakrete product data. Counts use 27 ft³ per yard, with no extra allowance. These yields belong to this mix, not every bag of the same weight.
The 40 ft³ slab example needs 67 bags at 0.60 ft³ each. Those bags yield 40.2 ft³. With 10% allowance, the 44 ft³ order needs 74 bags, yielding 44.4 ft³. The calculator shows the extra volume caused by whole-bag rounding separately.
Concrete mix is not cement
Bagged concrete mix includes cement and aggregates. This tool counts complete concrete-mix bags; it does not calculate a cement, sand and aggregate recipe, mortar or grout. For another mix, select Custom product yield and use its own label. For help identifying the right bag.
Estimate Concrete Material Cost
The concrete slab cost calculator uses your quoted ready-mix price or bag price. It estimates the concrete material subtotal, not the installed cost of a finished slab.
Ready-mix material = order volume × price per matching volume unit
Bagged material = whole bags × price per bag
Example prices only: 44 ft³ equals 1.6296 yd³ when displayed. At a hypothetical $150 per yd³, the unrounded volume gives $244.44. At a hypothetical $6 per bag, 74 bags cost $444.00.
Ready-mix may have minimum quantities, selling increments and short-load or delivery charges. Bagged quantities can include extra yield from rounding. Confirm the full supplier quote before comparing purchase options; labor, tax, reinforcement and formwork are not included here.
Sources & Methodology
Section volumes are calculated in cubic feet, multiplied by their quantities and added before allowance. Embedded post volume is subtracted only within the entered hole. Bag counts use the selected product yield and round up after summation; ready-mix and cost calculations use unrounded volume.
1 yd³ = 27 ft³; 1 ft = 0.3048 m; 1 m³ = 1,000 L. No product, price or extra allowance is assumed. Method and product yields checked October 23, 2026.
