Concrete Calculator Cost
How to Estimate Concrete Yards
Concrete is commonly ordered by the cubic yard, so a useful estimate turns real project dimensions into volume. The basic process is simple: measure the shape, keep the units consistent, calculate cubic feet, divide by 27, and add a practical allowance for waste and variation.
The basic slab formula
For a rectangular slab, measure length and width in feet. Convert thickness from inches to feet by dividing by 12. Then multiply the three dimensions together.
Example: a 12 foot by 16 foot patio that is 4 inches thick is 12 x 16 x 0.333 = about 64 cubic feet. Divide 64 by 27 to get about 2.37 cubic yards before waste allowance.
Step-by-step estimating process
- Measure the formed area after layout, excavation, and base preparation are close to final.
- Convert all dimensions to the same unit before multiplying.
- Calculate each section separately if the project has different thicknesses or shapes.
- Add the sections together to get the total cubic yards.
- Add a waste allowance before ordering or buying bags.
Estimating common concrete shapes
Slabs and pads: Use length x width x thickness. This applies to many patios, sidewalks, shed pads, garage slabs, and driveway sections.
Footings and curbs: Treat straight runs like long rectangular shapes. Multiply length by width by height or depth, then convert to cubic yards.
Round columns or piers: Use the circular area times height. The area of a circle is pi x radius squared. Make sure the radius is half the diameter.
Stairs: Break the stairs into simple rectangular parts when possible. Estimate treads, risers, landing areas, and any support section separately, then add them together.
Waste allowance matters
Even careful measurements can miss small changes in grade, form bowing, edge thickening, or material left in tools and wheelbarrows. A 5 to 10 percent allowance is common for many residential projects. Complex shapes, rough excavation, or hand-formed areas may need more.
From yards to cost
Once you know the estimated cubic yards, you can compare ready-mix delivery, bagged concrete, and local supplier options. Cost also depends on mix strength, delivery minimums, reinforcement, site preparation, and finishing. For budget planning, read the related Concrete Cost Guide.
Related concrete guides
FAQ
How many cubic feet are in one cubic yard of concrete?
One cubic yard contains 27 cubic feet. After calculating cubic feet, divide by 27 to convert the result to cubic yards.
Should concrete thickness be entered in inches or feet?
Either can work if units are consistent. A common method is to convert thickness from inches to feet before multiplying length, width, and thickness.
Why add extra concrete to an estimate?
Extra concrete helps cover uneven subgrade, form variation, spillage, and small measurement errors. Many residential estimates use a 5 to 10 percent allowance.