Slab size
Labor and extras
How the numbers are worked out
Area = length × width for each slab. Volume in cubic yards = area × thickness in inches ÷ 12 ÷ 27. Cubic yards to order = volume × (1 + waste %), rounded up to the next quarter yard. Concrete is priced per cubic yard, reinforcement and forming, placing and finishing per square foot, and demolition, delivery fees and haul-away as separate lines. If the total is below your minimum job charge, a minimum charge adjustment brings it up to the minimum.
Example with the defaults: a 20 × 20 ft slab is 400 sq ft. At 4 inches thick that is 400 × 4 ÷ 12 = 133.33 cubic feet, or 4.94 cubic yards. With 10% waste that is 5.43, rounded up to 5.5 cubic yards. Concrete 5.5 × $165 is $907.50, reinforcement 400 × $0.80 is $320 and forming, placing and finishing 400 × $4.50 is $1,800, so the job comes to $3,027.50 before tax. Rates are examples; use your own.
Tips for concrete estimates
- Measure the thickness you will actually pour, including footings or thickened edges, not just the nominal slab depth; extra depth adds up quickly.
- Check the supplier's short-load fee and minimum order before you quote small pours; a 2 yard job can cost more per yard than a 6 yard job.
- List demolition and haul-away of the old slab as their own lines so the customer sees what is included.
- Check your rates cover your costs and target margin with the job price calculator and fine-tune waste with the material waste calculator.
Frequently asked questions
How many cubic yards of concrete do I need?
Multiply length by width (in feet) to get the area, multiply by the thickness in inches divided by 12 to get cubic feet, then divide by 27 to get cubic yards. A 20 x 20 ft slab that is 4 inches thick is 133.3 cubic feet, or about 4.94 cubic yards, before waste.
How much extra concrete should I order?
Most contractors add about 5 to 10 percent for uneven subgrade, spillage and over-excavation, and more for footings or irregular shapes. Running short means a costly second delivery, so the 10 percent default here is an example, not a rule.
How do contractors price a concrete slab?
Many quote a price per square foot that includes forming, placing, finishing and reinforcement, then check it against material cost. Others price concrete by the cubic yard plus labor and separate lines for demolition, haul-away and short-load fees. The defaults here are examples, not market prices.
Can I send this as an estimate?
Yes. Click Turn into an estimate. Concrete, reinforcement, labor, demolition and haul-away become line items in the free Estimate & Invoice Maker, where you add your logo and customer details and download a PDF. Your business details from earlier drafts are kept.
Estimates for planning only. Rates shown are examples, not market prices; use your own.
Related: Free concrete estimate template · Drywall estimate calculator · Job price calculator