Calculators / Concrete
Concrete Calculator
To calculate concrete, enter the slab length, width, and thickness; this tool returns the volume in cubic yards, the number of 80 lb bags, and a cost estimate. One 80 lb bag yields about 0.6 cubic feet.
Real math, not AI guesses.
You need
1.3 cubic yards
Estimated cost
~$354
- Volume
- 33.3 cu ft
- With 5% waste
- 35 cu ft
- Cubic yards
- 1.3
- 80 lb bags (0.6 cu ft each)
- 59
Estimate only — actual quantities and prices vary by region and supplier. Verify with a professional before purchasing. Default price is a national average (as of 2026-06); edit it to match your supplier.
How to calculate concrete
The formula: cubic yards = (length × width × thickness⁄12) ÷ 27
- Measure the length and width in feet and the thickness in inches.
- Convert thickness to feet (inches ÷ 12), then multiply length × width × thickness for cubic feet.
- Divide cubic feet by 27 to get cubic yards.
- For bags, divide cubic feet by the bag yield (0.6 cu ft for an 80 lb bag) and round up.
Prices shown are national averages (as of 2026-06) and vary by region, brand, and supplier. They are estimates, not quotes.
How much does a concrete slab cost?
A basic 4-inch concrete slab costs roughly $4–$8 per square foot in materials and delivery. Poured and finished by a pro, expect $6–$12 per square foot installed, including forming, pouring, and finishing. For a 10×10 patio (100 sq ft), that is about $600–$1,200 installed. Ready-mix delivery runs roughly $120–$170 per cubic yard, with short-load fees on small pours.
What drives the cost
- Thickness and reinforcement: rebar, wire mesh, and a 5–6 inch driveway slab cost more than a 4-inch patio.
- Finish: a broom finish is cheapest; stamped, colored, or exposed-aggregate concrete costs more.
- Site prep: grading, a gravel base, and forms add cost.
- Small pours pay short-load fees; ready-mix is cheaper per yard than bags at volume.
- Truck or pump access — hard-to-reach pours raise labor.
DIY vs. hiring a pro
Small slabs (a shed pad, a few steps) are DIY-able with bagged mix, but concrete is unforgiving — you get one window to place and finish before it sets. For anything large, a driveway, or a slab that must be flat and level, ready-mix delivery plus a finisher is usually worth it. Get a couple of quotes and confirm whether base prep and forms are included.
Installed and labor figures are national-average ranges, not quotes — get a few local estimates for your project.
Concrete FAQ
How many bags of concrete are in a cubic yard?+
A cubic yard is 27 cubic feet. An 80 lb bag yields about 0.6 cubic feet, so you need roughly 45 80 lb bags per cubic yard.
How thick should a concrete slab be?+
4 inches is standard for patios and walkways; 5–6 inches for driveways and areas with heavier loads.
How much does a 10×10 concrete slab cost?+
A 10×10 slab is 100 sq ft. At $6–$12 per square foot installed, that is about $600–$1,200 for a pro; in bagged-mix materials alone it is roughly $300–$500.
Is it cheaper to use bags or ready-mix concrete?+
Bags are cheaper for very small pours, but mixing labor adds up fast. Past about 1 cubic yard (≈45 80 lb bags), ready-mix delivery is usually cheaper and far less work.