Concrete Calculator
Estimate one section now, or combine up to 25 slabs, cylinders, and annular sections in one receipt.
Private by design: dimensions stay in this tab. The calculation needs no storage, uploads, permissions, or network connection after the page loads; analytics receives only categories such as shape mix and section count.
Default example: one 10 ft × 10 ft × 4 in rectangular section. Select Calculate concrete to see the receipt.
Calculate several concrete sections together
Use a rectangular prism for slabs, walls, and continuous footings. Use a solid cylinder for columns, round footings, or a post hole when no inner object is deducted. Use an annular cylinder for a tube or for the circular volume left after subtracting a smaller circular post. Each dimension can use feet, inches, yards, meters, or centimeters, so one project can mix units without manual conversions.
Formulas and exact unit conversion
A rectangular section uses length × width × depth. A solid cylinder uses π × diameter² ÷ 4 × height. An annular cylinder uses π × (outer diameter² − inner diameter²) ÷ 4 × height. The engine derives length factors from the exact international inch definition and uses the NIST values 1 yd³ = 27 ft³ and 1 ft³ = 0.028316846592 m³.
Every section subtotal stays unrounded while the project is added. Waste, bag division, whole-bag ceiling, and optional ready-mix ceiling all use that unrounded total. Display rounding changes only the receipt, not later calculations.
Waste, bag yield, and ready-mix rounding
Waste starts at 0% because no percentage applies to every site. If you add a value, the receipt shows raw volume, waste volume, and adjusted volume separately. An optional ready-mix increment rounds the adjusted cubic-yard total upward only when you choose 0.25, 0.5, or 1 yd³.
Bag yield is also optional and editable. The QUIKRETE Concrete Mix No. 1101 specification lists approximate examples of 0.30 ft³ for a 40 lb bag, 0.45 ft³ for a 60 lb bag, and 0.60 ft³ for an 80 lb bag. Those examples are product-specific, not universal defaults. Check the current label for the product you will use.
Planning boundary
This estimates material volume from the dimensions and assumptions entered. Actual needs vary with excavation, subgrade, forms, spillage, product yield, supplier minimums, and site conditions. Check the product label and supplier, and use a qualified professional for structural dimensions, reinforcement, mix design, loads, or code compliance.
The calculator does not estimate price, tax, delivery fees, financing, ordering, compressive strength, reinforcement, load capacity, code compliance, or recommended slab thickness. It does not save a project or contact a supplier.
Frequently asked questions
How do I calculate how much concrete I need?
Add each rectangular, solid cylindrical, or annular section with its own dimensions, units, and quantity. The calculator converts every length to feet, calculates each exact subtotal, sums the unrounded volumes, and then applies your waste percentage.
How many cubic feet are in a cubic yard of concrete?
There are exactly 27 cubic feet in one cubic yard. This calculator keeps the unrounded cubic-foot total internally and divides by 27 for the cubic-yard result.
Can I combine slabs, columns, and post holes?
Yes. Add up to 25 mixed sections. Use a rectangular prism for a slab, wall, or footing; a solid cylinder for a round footing or column; and an annular cylinder when subtracting a circular inner diameter from a larger circular hole or tube.
What waste percentage should I use?
There is no universal waste percentage. The field starts at 0% and accepts a custom value from 0% through 25%. Excavation, subgrade, forms, spillage, and site conditions can change actual needs, so confirm the assumption for your project.
How does the concrete bag estimate work?
Enter the product label's yield in cubic feet per bag. The calculator divides the unrounded adjusted volume by that editable yield, shows the raw bag count, and rounds up to the next whole bag. It does not assume one universal package yield.
Does this calculator estimate concrete price or structural requirements?
No. It does not estimate price, tax, delivery, strength, reinforcement, load capacity, code compliance, or a recommended thickness. It is a material-volume estimate, not engineering or ordering advice.