Concrete calculator
Turn rectangular dimensions into a purchase sheet. Compare bag sizes, enter the actual product yield, or select ready-mix for a supplier quote. The initial 10x12 ft example at 4in depth includes 10% waste: 1.63 cu yd, 74 bags of 80lb premix, or 98 bags of 60lb premix. Adjust the calculator below for your project.
For rectangular volumes. Use the depth specified for your project; this calculator estimates material quantity, not structural design.
Quantities to confirm
Concrete purchase sheet
The starting yield is an example for this bag size. Replace it with the product label; bag weight alone does not determine yield.
- 80 lb bags44 cu ft with allowance ÷ 0.6 cu ft per bag; rounded up.
- 74bags
What this estimate assumes
- Raw volume: 40 cu ft. Waste allowance: 10%.
- Rectangular volume only; the entered depth comes from your design.
- Bag yield entered: 0.6 cu ft/bag. Whole bags provide 0.4 cu ft above the volume with allowance.
- Only the selected supply method is listed; alternatives are not added together.
Name your project & add notes Optional
Includes your quantities, assumptions and space to record the supplier, confirmed quantity, quote and delivery. No account required.
How to check this list before buyingCompare standard bag sizes and volume
Material totals
1 cu yd = 27 cu ft. Bag counts are rounded up to whole bags; volumes are displayed to two decimal places. The two bag sizes are alternatives.
Concrete shopping list
Choose one supply method; do not add these quantities together.
Yield assumptions: one 80lb bag = 0.6 cu ft; one 60lb bag = 0.45 cu ft. Check the actual bag label; products can differ.
The volumes above include the stated waste allowance. Confirm yield, ready-mix ordering increments and delivery requirements with your supplier before purchasing.
BuildTotals.com · Prepared: __________ · buildtotals.com/tools/concrete-calculator
Initial sample trace: 10ft x 12ft slab, 4in depth
- Volume = 10 x 12 x (4/12) = 40.00 cu ft
- With 10% waste = 40.00 x 1.10 = 44.00 cu ft
- Cubic yards = 44.00 / 27 = 1.63 cu yd
- 80lb bags (0.6 cu ft/bag) = ceil(44.00 / 0.6) = 74 bags
- 60lb bags (0.45 cu ft/bag) = ceil(44.00 / 0.45) = 98 bags
This fixed example explains the initial inputs. The calculator and printable list use your current inputs. Confirm actual product yield, delivery minimums, and the final order quantity with your supplier.
Related projects
When to hire a contractor
Plan the work around site access, equipment, placement needs, and your experience. A volume estimate does not determine whether a pour is suitable for DIY work. Consult a qualified professional for structural design or construction requirements.
How to use the concrete calculator
- Measure the rectangular length and width in feet, and use the depth in inches from your actual design.
- For the initial 10ft x 12ft example at 4in depth, volume = 10 x 12 x (4/12) = 40.00 cu ft.
- With the example's 10% waste, the volume is 44.00 cu ft, or 1.63 cu yd. Adjust the allowance for your project.
- At the stated yields, the example requires 74 whole 80lb bags or 98 whole 60lb bags. Choose one supply method and confirm product yield or ready-mix delivery quantity with your supplier.
- Adjust the calculator for your project and print the current shopping list.
Depth comes from your actual design; the sample depth is only an input for the estimate. This calculator supports rectangular volumes. For a round footing or column, use a calculation based on circular area; do not enter its diameter as both length and width here.
Frequently asked questions
How many 80lb bags of concrete do I need for a 10x12 slab at 4 inches?
The initial rectangular example is 40.00 cubic feet before waste. With 10% waste, that is 44.00 cubic feet. At 0.6 cubic feet per 80lb bag, round up to 74 whole bags. The alternative is 98 whole 60lb bags at 0.45 cubic feet per bag, or 1.63 cubic yards of ready-mix. Confirm the product yield or delivery quantity with your supplier.
How do I convert cubic feet to cubic yards?
Divide by 27. There are 27 cubic feet in one cubic yard. For the initial 10x12 slab at 4 inches, 40.00 / 27 = 1.48 cu yd before waste. With 10% waste, 44.00 / 27 = 1.63 cu yd.
When should I order ready-mix instead of bags?
Compare quotes for your calculated quantity, including delivery minimums and fees, site access, mixing equipment, and placement needs. The cost and practical choice depend on your project and local suppliers. Confirm the final delivery quantity before ordering.
What waste factor should I use for concrete?
The initial example uses 10% as a planning allowance. Set a value from 0% to 30% based on your measurements, form and base conditions, and supplier or contractor advice. This calculator models a rectangular volume; separate volumes or another shape require their own calculation.