Hardscaping / Field guide
How Many Yards of Concrete Do I Need?
Measure the pour, convert inches to feet, and turn cubic feet into a practical ready-mix quantity.
Last updated September 25, 2026. Methodology, sources & assumptions.
Open the concrete calculator01 / The details
Measure the slab dimensions
Measure the finished length and width in feet, then use the thickness specified for the project in inches. For a rectangle, footprint area is length × width. Split an irregular outline into rectangles, calculate each part, and add their volumes.
Keep units consistent. Divide a thickness in inches by 12 to convert it to feet before multiplying. If you measured length or width in inches, divide those measurements by 12 as well.
- Length and width: feet (ft).
- Thickness: inches (in), converted to feet before finding cubic feet.
- Use the planned concrete dimensions, not the outside dimensions of a larger work area.
From measurements to yards
Thickness in feet = inches ÷ 12
Cubic feet = length × width × thickness in feet
Cubic yards = cubic feet ÷ 27
02 / The details
Convert cubic feet to cubic yards
First calculate cubic feet: length (ft) × width (ft) × thickness (in) ÷ 12. Then divide cubic feet by 27 because one cubic yard contains 27 cubic feet.
Combined formula: cubic yards = length (ft) × width (ft) × thickness (in) ÷ 12 ÷ 27. This estimates a simple, uniform rectangular pour; calculate separate shapes individually and add them together.
- Thickness in feet = thickness in inches ÷ 12.
- Cubic feet = length × width × thickness in feet.
- Cubic yards = cubic feet ÷ 27.
03 / The details
Concrete yard examples
10 × 10 ft slab at 4 in thick: 10 × 10 × 4 ÷ 12 ÷ 27 = about 1.23 cubic yards before allowance. Adding 5%–10% gives about 1.30–1.36 cubic yards.
Driveway example: a 20 × 20 ft area at 5 in thick is about 6.17 cubic yards before allowance, or about 6.79 cubic yards with 10% extra. The 5-inch thickness is only an arithmetic example, not a driveway design recommendation.
Sidewalk example: a 30 × 4 ft walk at 4 in thick is about 1.48 cubic yards before allowance, or about 1.63 cubic yards with 10% extra.
04 / The details
Add a 5%–10% ordering allowance
After calculating the base volume, multiply by 1.05 for 5% extra or 1.10 for 10% extra. The right allowance depends on the formwork, site, depth variation, spillage, and placement conditions; use the range as a planning starting point, not a guarantee.
Do not round the estimate down. Ask the ready-mix supplier how quantities are rounded, whether a minimum load applies, and whether a short-load fee or delivery charge affects your order.
05 / The details
Confirm the project design before ordering
A volume estimate does not determine a safe slab thickness or specify reinforcement, joints, subgrade, or concrete strength. For driveways, garages, structural slabs, or heavy loads, verify the design with approved plans, local requirements, or a qualified professional.
If the project also needs an aggregate base, estimate that layer separately using its specified depth and material. Concrete quantity and base quantity are different calculations.
The short version
Convert thickness from inches to feet, calculate cubic feet, divide by 27, then add a site-appropriate 5%–10% planning allowance.
Common questions
Concrete quantity FAQs
How many cubic yards do I need for a 10 × 10 slab?
At 4 inches thick, a 10 × 10 ft slab contains about 1.23 cubic yards before allowance. Adding 5%–10% gives about 1.30–1.36 cubic yards. Confirm the design thickness and supplier order increments for your project.
How many yards of concrete do I need for a 4-inch slab?
It depends on the slab area. At 4 inches thick, cubic yards = length in feet × width in feet ÷ 81. A 10 × 10 ft slab is about 1.23 cubic yards before allowance; add a project-appropriate amount for ordering.
Should I order extra concrete?
A 5%–10% planning allowance is a common starting range, but the appropriate amount depends on form accuracy, depth variation, site access, and placement. Check the quantity and delivery rules with your supplier, and do not treat the allowance as a substitute for accurate measurements.
How do I convert cubic feet to cubic yards?
Divide cubic feet by 27. For example, 54 cubic feet ÷ 27 = 2 cubic yards. If thickness is in inches, first divide it by 12 when calculating cubic feet.
Does this estimate tell me how thick a driveway should be?
No. This page estimates volume from a chosen thickness; it does not design the driveway. Confirm thickness, base, reinforcement, and other requirements for the soil, loads, climate, and local rules.
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