Concrete Calculator
Estimate concrete for slabs, rectangular footings, multiple rectangles or cylindrical columns. Review converted volume, waste, bag yield and material cost before ordering.
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How to Use the Concrete Calculator
Choose slab, footing, multiple rectangles or column mode. Imperial rectangles use feet for length/width and inches for thickness; metric uses meters and centimeters. Column diameter is inches or centimeters, with height in feet or meters. Add sections, set waste, then optionally select a labeled bag yield or bulk price. Reset returns to the original slab example.
Formula and Explanation
Rectangular volume = length × width × thickness in consistent units Column volume = π × (diameter / 2)² × height × quantity Order volume = total volume × (1 + waste / 100) Bags = ceil(order volume / mixed yield per bag) 1 cu yd = 27 cu ft; 1 cu ft = 0.028316846592 m³
The original rectangular slab calculation is reused without changing its formula. Imperial results convert to cubic yards and cubic meters without rounding intermediate volume. Bag weights identify illustrative presets, not a mass-to-volume conversion: 40/60/80 lb loads 0.30/0.45/0.60 cubic feet of assumed mixed yield. Edit the yield and choose cubic feet, cubic meters or liters to match your product. Cost uses either whole bags or waste-adjusted bulk volume, not both.
Materials estimate only, not structural design. It does not determine suitable slab or footing dimensions, reinforcement, soil preparation or compliance. Confirm actual bag yield and supplier increments. Irregular excavations, spillage and overlaps affect volume; count every section once. Delivery, labor, tax and accessories are excluded. Shape changes use the relevant displayed sections only.
Worked Example
A 10 × 10 ft slab at 4 inches thick uses 33.3333… cu ft. With 10% waste, allow 36.6666… cu ft = 1.3580… cu yd = about 1.0383 m³. At an illustrative 0.60 cu ft per bag, buy 62 bags; at $7 each, material cost is $434. A separate 18-inch-diameter, 8 ft column uses π × 0.75² × 8 = about 14.1372 cu ft before waste.
Frequently Asked Questions
Can I estimate cylindrical columns?
Yes. Column volume uses π times radius squared times height, multiplied by quantity. Enter diameter, not radius, and use the unit shown beside each field.
How are metric measurements handled?
Metric rectangle length/width and column height use meters; rectangle thickness and column diameter use centimeters. They convert to consistent length units before volume is calculated. Results include cubic feet, cubic yards and cubic meters.
Does selecting an 80 lb bag determine the volume?
No. Selecting a bag loads a labeled illustrative yield, which remains editable. The calculation divides volume by mixed yield, not by bag weight. Confirm the actual manufacturer yield.
Does cost use bags or bulk volume?
Choose one price basis. Bag cost uses rounded-up bags. Bulk cost uses the unrounded waste-adjusted cubic yards or cubic meters. No delivery or structural-design cost is included.
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