Concrete Calculator
Estimate concrete for slabs, footings, walls, and round columns in cubic yards, cubic feet, cubic meters, and bags.
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Quick slab presets
Waste is applied after multiplying identical pours. Bag yields are typical estimates; check the yield printed on your product.
Concrete Slab Measurement
Measure the length and width inside the forms and the depth of the pour. Use the thickness specified for your project; the diagram shows where each slab measurement is taken.
How to Use the Concrete Calculator
Choose the project shape and enter the finished concrete dimensions. The calculator keeps the base volume separate from waste and rounds the suggested ready-mix order upward, so you can see exactly where the ordering figure comes from.
- Select the shape: Choose slab, footing, wall, or column. Use separate calculations for sections with different dimensions.
- Choose units: Enter long dimensions in feet or meters and thickness, width, depth, or diameter in inches or centimeters as labeled.
- Enter dimensions and quantity: Quantity multiplies the geometry before the waste allowance is applied. It is useful for identical columns, pads, or footings.
- Set ordering assumptions: Adjust the waste percentage, select the bag size, and optionally enter a current ready-mix price from a local quote.
- Review the result: Compare the unrounded calculated total, suggested quarter-yard ready-mix order, bag count, and assumptions before buying material.
The quick presets are starting points for common slab dimensions, not construction recommendations. Use the dimensions shown on your plans or confirmed by a qualified local professional.
Concrete Volume Formulas
Use one unit system throughout each formula. For imperial calculations, convert inches to feet by dividing by 12. The calculator converts metric entries internally and displays both cubic yards and cubic meters.
Slabs, Footings, and Walls
Rectangular volume = length × width × depth
The same rectangular-prism formula applies to a slab, continuous footing, or wall. Only the meaning and input unit of each dimension changes.
Round Columns
Cylinder volume = π × radius² × height
Radius is half the column diameter. Convert the diameter to feet before using the imperial formula.
Quantity, Waste, and Ordering
Base volume = volume per item × quantity
Calculated total = base volume × (1 + waste percentage ÷ 100)
Cubic yards = cubic feet ÷ 27
The suggested ready-mix order rounds the calculated total up to the next 0.25 cubic yard. Suppliers may use different order increments or minimums, so confirm before ordering.
Bag Estimate
Bag count = calculated cubic feet ÷ yield per bag, rounded up to a whole bag. The calculator uses typical yields of 0.30 ft³ for 40 lb, 0.375 ft³ for 50 lb, 0.45 ft³ for 60 lb, and 0.60 ft³ for 80 lb bags. Product yield controls the final quantity.
Concrete Slab Example
Suppose a patio is 12 feet long, 12 feet wide, and 4 inches thick, with one pour and a 10% waste allowance.
- Convert thickness: 4 inches ÷ 12 = 0.333 feet.
- Base volume: 12 × 12 × 0.333 = 48 cubic feet.
- Convert to yards: 48 ÷ 27 = 1.78 cubic yards.
- Add 10%: 1.78 × 1.10 = 1.96 cubic yards.
- Round for ordering: The next 0.25 cubic-yard increment is 2.00 cubic yards.
- 80 lb bag alternative: 52.8 ft³ ÷ 0.60 ft³ per bag = 88 bags.
Planning result: The calculator suggests 2.00 cubic yards of ready-mix or about 88 typical 80 lb bags. Confirm product yield, delivery charges, order minimums, and the final volume with the supplier.
Concrete Ordering Tips
Concrete quantity depends on the built or excavated dimensions, not only the nominal drawing dimensions. Check the site before placing an order.
- Measure several points: Subgrade depth and excavation width can vary. Use representative measurements and increase the allowance when the shape is irregular.
- Separate different sections: Calculate slabs, thickened edges, grade beams, footings, walls, and columns individually when their dimensions differ, then combine the totals.
- Ask about supplier rules: Confirm minimum order, quarter- or half-yard increments, short-load charges, truck capacity, delivery access, waiting time, and cancellation policy.
- Use the product yield: Bag weights do not guarantee identical yield across every mix. Replace the typical calculator assumption with the manufacturer's stated yield when making a final purchase.
- Plan the base separately: Use the Gravel Calculator for the compacted aggregate layer; do not include base material in the concrete thickness.
- Follow the project specification: Thickness, reinforcement, mix strength, joints, curing, and code requirements affect performance but are outside a volume calculation.
Frequently Asked Questions
How many cubic yards of concrete do I need for a 10x10 slab?
A 10 by 10 foot slab that is 4 inches thick has a base volume of about 1.23 cubic yards. With a 10% allowance, the calculated total is about 1.36 cubic yards. The calculator rounds a suggested ready-mix order up to the next quarter-yard, but you should confirm the supplier's minimum order and increment.
How many 80 lb bags of concrete make a cubic yard?
If an 80 lb bag yields 0.60 cubic feet, 45 bags produce about one cubic yard because one cubic yard contains 27 cubic feet. Actual yield varies by product, so use the yield printed on the bag when ordering.
What waste allowance should I use for concrete?
Ten percent is a common planning allowance for small pours with uneven subgrade, form movement, spills, and measurement variation. A well-controlled pour may need less, while irregular excavations may need more. Set the calculator's waste field to match the project and supplier guidance.
What is the difference between cubic yards and cubic feet?
A cubic foot measures one foot on each side. A cubic yard measures three feet on each side, so one cubic yard equals 27 cubic feet. Ready-mix is commonly ordered by the cubic yard, while bag yield is often listed in cubic feet.
How much does a cubic yard of concrete cost?
Concrete pricing varies by location, mix design, order size, delivery distance, fuel charges, and short-load fees. Ask a local ready-mix supplier for the current price per cubic yard, enter it in the calculator, and add any delivery or service fees from the quote separately.
How do I calculate concrete for a footing?
Multiply the footing's total length by its width and depth after converting every measurement to the same unit. Divide cubic feet by 27 for cubic yards, multiply by the number of identical footings, and then add the selected waste allowance.
How do I calculate concrete for a wall?
Multiply wall length by wall height by wall thickness, using consistent units. Openings should be deducted only when their dimensions are known and the project specification permits it. Use separate calculations when wall sections have different thicknesses or heights.
How do I calculate concrete for a round column?
Convert the diameter to a radius, then calculate π times radius squared times height. That gives the cylinder volume. Multiply by the number of identical columns, convert to cubic yards if needed, and add the chosen waste allowance.
Should I use ready-mix or bagged concrete?
Bagged mix can be practical for small pours and repairs. As volume and bag count increase, ready-mix may reduce labor and provide a more consistent placement. Compare the calculator's bag count with local ready-mix minimums, delivery fees, site access, mixing capacity, and placement time.
Does the calculator replace a concrete supplier or engineer?
No. It is a material-planning estimate based on the dimensions and assumptions entered. Confirm slab thickness, footing dimensions, reinforcement, concrete strength, site conditions, code requirements, and final order quantity with the project plans and qualified local professionals.