Calculator
Concrete Calculator
Calculate how much concrete you need for a rectangular slab or pad in cubic yards, cubic feet, and cubic meters.
Use this calculator to estimate the geometric volume of concrete for a rectangular slab or pad. Enter length, width, and thickness in US customary or metric units. The engine converts everything to meters, multiplies length × width × thickness, then reports volume in cubic yards (yd³), cubic feet (ft³), and cubic meters (m³).
You can optionally add a waste percentage and your own unit price per cubic yard to estimate material cost. Structural design, reinforcement, and site conditions are outside the scope of this tool and should be reviewed by a qualified professional when required.
Project dimensions
All calculations run on the audited CostRafter PHP engine (concrete_volume v1.0.0).
Important disclaimer
This tool estimates geometric concrete volume for a rectangular slab or pad. It does not certify structural design and does not account for reinforcement, compaction, forms, or special site conditions. Always verify with a qualified professional and local building requirements before ordering materials.
About this calculator
How to Use the Concrete Calculator
Enter the three dimensions of a rectangular slab or pad:
Length — the longer horizontal side (feet, inches, meters, or centimeters).
Width — the shorter horizontal side, using the same unit choices.
Thickness — the depth of the pour (inches, centimeters, millimeters, feet, or meters).
Choose a waste percentage if you want an ordering allowance (the default is 10%). Leave cost blank unless you want a material-cost estimate based on a price you already know. Press calculate to see base volume and volume with waste in yd³, ft³, and m³.
How to Calculate Concrete Volume
For a rectangular slab, volume is:
Volume = Length × Width × Thickness
All inputs are converted to meters before multiplying, then the result is converted to cubic yards and cubic feet for display. That keeps US customary and metric projects on one consistent calculation path.
Useful relationships:
1 foot = 0.3048 meters; 1 inch = 0.0254 meters.
1 cubic yard = 27 cubic feet.
1 cubic yard ≈ 0.7646 cubic meters (exact factor used by the engine: 0.764554857984).
Cubic Yards vs Cubic Feet
Ready-mix concrete in the United States is commonly ordered in cubic yards. Smaller DIY estimates and board-foot style checks often use cubic feet. Metric projects usually plan in cubic meters.
This calculator always shows all three. To convert manually: divide cubic feet by 27 to get cubic yards, or multiply cubic yards by 27 to get cubic feet.
How Much Extra Concrete Should You Order?
Waste percentage is a selectable estimate, not a universal rule. The default of 10% is a common planning starting point for spills, uneven subgrade, and form variation. You may choose 0% for a pure geometric volume, or another value up to 30% if your project conditions call for a larger allowance.
Do not treat the waste field as a substitute for a contractor’s takeoff. Complex shapes, slopes, over-excavation, and pump loss can change how much concrete you should order.
Concrete Volume Calculation Examples
The following examples were computed with CostRafter’s concrete_volume engine (v1.0.0).
Imperial example — patio slab
A rectangular patio measuring 10 ft × 12 ft × 4 in thick:
Base volume: 40 ft³ = 1.4815 yd³ = 1.1327 m³
With 10% waste: 44 ft³ = 1.6296 yd³ = 1.2459 m³
Quick check without the calculator: 10 × 12 × (4 ÷ 12) = 40 cubic feet; 40 ÷ 27 ≈ 1.4815 cubic yards.
Metric example — equipment pad
A pad measuring 3 m × 2 m × 10 cm thick:
Base volume: 0.6 m³ = 21.1888 ft³ = 0.7848 yd³
With 5% waste: 0.63 m³ = 22.2482 ft³ = 0.8240 yd³
Quick check: 3 × 2 × 0.10 = 0.6 cubic meters.
Default form dimensions
The form defaults to 20 ft × 12 ft × 4 in with 10% waste, which yields about 2.9630 yd³ base and 3.2593 yd³ with waste. Change the inputs to match your project.
How to Estimate Concrete Material Cost
If you enter a price per cubic yard, the calculator multiplies that price by the volume with waste in cubic yards. For example, using the 10 × 12 × 4 in patio with 10% waste (1.6296 yd³) and a user-entered price of $150 per cubic yard produces about $244.44.
That figure is only as accurate as the price you supply. CostRafter does not display market quotes, supplier rates, or delivery fees. Labor, reinforcement, forms, finishing, and tax are not included.
Common Calculation Mistakes
Mixing units (for example, length in feet and thickness in inches) without converting — use the unit selectors so the engine converts for you.
Forgetting to convert thickness from inches to feet when doing a manual check (4 inches = 4/12 feet).
Ordering exactly the base volume with no allowance when the pour conditions usually need some extra.
Assuming a rectangular volume covers irregular shapes, steps, or thickened edges — break those into separate rectangles or get a professional takeoff.
Confusing bag yield with ready-mix cubic yards when shopping bagged mix.
Important Assumptions and Limitations
Geometry is a single rectangular slab or pad (length × width × thickness).
Results are geometric volume estimates, not structural design, load ratings, or code compliance.
Reinforcement, compaction, forms, slopes, and site conditions are not modeled.
Waste percentage is optional planning input, not a mandated overage.
Optional cost uses only the unit price you enter; it is not a market price recommendation.
If your project involves foundations, retaining structures, public sidewalks, or engineered slabs, have plans and quantities reviewed by a qualified professional and confirm requirements with local building authorities before ordering materials.
Related guides
Practical planning guides paired with this calculator.
