10 × 20 ft patio, 4 in thick
10 ft × 20 ft × 4 in · 10% waste
- Base volume
- 2.469 yd³
- With waste
- 2.716 yd³
- 80 lb bags to buy
- 123
Material calculator
Concrete Calculator
Calculate concrete volume, a ready-mix order quantity, and bag counts for slabs, walls, footings, and round columns using US, metric, or mixed units.
How much concrete do you need to order?
Volume, ready-mix order, and bags
Project inputs
Enter dimensions
Estimate
Concrete to order
Recommended ready-mix order
5.5yd³
4.205 m³ equivalent
Volume breakdown
Base concrete volume4.94 yd³
Waste allowance0.49 yd³
Waste-adjusted volume5.43 yd³
Recommended order5.5 yd³
Cubic feet146.67 ft³
Cubic meters4.153 m³
Bag estimates
| Bag size | Estimated | Buy |
|---|---|---|
| 40 lb bags | 488.89 | 489 |
| 60 lb bags | 325.93 | 326 |
| 80 lb bags | 244.44 | 245 |
Estimated counts use 0.30, 0.45, and 0.60 ft³ yields respectively. Purchase quantities always round up; verify the product label.
How it's calculated
Slab volume
Length × width × thickness × quantity
Then add 10% waste and round the cubic-yard order upward to the next 0.25 yd³.
Worked examples
Concrete estimates for common projects
Every example below is calculated with the same engine as the calculator, using a 10% waste allowance.
20 × 20 ft garage slab, 4 in thick
20 ft × 20 ft × 4 in · 10% waste
- Base volume
- 4.938 yd³
- With waste
- 5.432 yd³
- 80 lb bags to buy
- 245
Fence post footing
12 in × 12 in × 36 in rectangular footing · 10% waste
- Base volume
- 0.111 yd³
- With waste
- 0.122 yd³
- 80 lb bags to buy
- 6
Concrete wall
12 ft long × 8 ft high × 8 in thick · 10% waste
- Base volume
- 2.37 yd³
- With waste
- 2.607 yd³
- 80 lb bags to buy
- 118
Method
How to calculate concrete volume
Measure each dimension, convert them to compatible units, apply the shape formula, and then add a realistic waste allowance. Keep full precision until presenting the result or selecting an ordering increment.
Concrete for slabs
Use the concrete slab calculator mode to multiply length by width by thickness, then by the number of identical slabs. Thickness can be entered in inches while length and width use feet.
Concrete for footings
The concrete footing calculator mode multiplies length by width by depth and quantity. Calculate groups with different footing sizes separately, then combine them.
Concrete for walls and columns
The concrete wall calculator uses length × height × thickness. Round columns use π × radius² × height. Openings, returns, and sections with another thickness should be measured separately.
How much extra concrete should you order
Waste covers reasonable variation in forms, excavation, spillage, and handling. This concrete calculator with waste keeps the base amount, allowance, adjusted volume, and rounded order visible separately.
How many bags of concrete do you need
The concrete bag calculator divides adjusted cubic feet by a centralized yield for 40, 60, or 80 lb bags. It shows the fractional estimate and a whole-bag purchase quantity.
Ready-mix vs bagged concrete
Bagged mix may suit small pours where on-site mixing is manageable. Ready-mix is often more practical for larger continuous placements; confirm delivery minimums, access, timing, and supplier order increments.
How estimated concrete cost is calculated
Price is optional. When supplied, the calculator multiplies price per cubic yard by the base volume, adjusted volume, and rounded ready-mix order separately, without combining ready-mix and bag costs.
Common questions
Concrete calculator FAQ
How many cubic yards of concrete do I need?
Enter the dimensions and quantity for your slab, footing, wall, or round column. The calculator normalizes the units, finds the base volume, applies your waste allowance, and converts the result to cubic yards. One cubic yard contains 27 cubic feet.
How many cubic feet are in a cubic yard of concrete?
One cubic yard contains exactly 27 cubic feet. Divide cubic feet by 27 to convert a volume to cubic yards.
How much extra concrete should I order for waste?
A 10% waste factor is a common planning starting point, but the right allowance depends on excavation accuracy, formwork, spillage, site access, and supplier requirements. This calculator allows 0% to 30% and then rounds the ready-mix order upward to the next 0.25 cubic yard.
How many 80 lb bags are in a cubic yard?
At an approximate yield of 0.60 cubic feet per 80 lb bag, one cubic yard requires about 45 bags. Product yields vary, so verify the yield printed on the bag before purchasing.
Can I calculate concrete for a footing?
Yes. Select Footing and enter its length, width, and depth. Use quantity for identical footings; calculate different footing sizes separately and add the results.
Can I calculate concrete for a wall or column?
Yes. Wall mode uses length × height × thickness. Column mode calculates a solid round column with π × radius² × height. Both modes support a quantity of identical sections.
Should I order ready-mix concrete or use bags?
Bags can be practical for small pours and repairs, while ready-mix is often easier for larger, continuous pours. Consider total volume, mixing capacity, placement time, access, delivery minimums, and short-load charges before deciding.
Does the calculator support metric measurements?
Yes. Each dimension can use inches, feet, yards, millimeters, centimeters, or meters, including mixed-unit inputs. Results are shown in cubic yards, cubic feet, and cubic meters.
How many bags of concrete do I need?
Divide total cubic feet including waste by the product yield and round up. This concrete bag calculator uses approximate yields of 0.30 ft³ for 40 lb, 0.45 ft³ for 60 lb, and 0.60 ft³ for 80 lb bags.
Does the estimated cost include delivery and labor?
No. The concrete cost calculator shows base material cost, cost including waste, and the rounded ready-mix order cost from the price per cubic yard you enter. It excludes delivery, taxes, short-load fees, pumping, tools, reinforcement, formwork, and labor.
More tools
Related calculators
- Gravel CalculatorCalculate gravel volume and tonnage for driveways, paths, and landscaping beds.
- Asphalt CalculatorCalculate asphalt volume, short tons, and material cost for driveways, roads, and parking areas.
- Deck CalculatorCalculate how many decking boards you need from deck dimensions or known area, including board size, gaps, waste allowance, and estimated material cost.
- Fence CalculatorCalculate fence pickets, panels, posts, and rails for one straight fence run, including spacing, gaps, waste allowance, and optional material cost.