🏗️ Contractor-Grade Tool
Concrete Calculator
Calculate cubic yards, cubic feet, and bag count for slabs, footings, columns, and steps. Includes 10% waste factor and real-time cost estimation. Covers Quikrete, Sakrete, and ready-mix.
Driveway: 6", Patio: 4", Walkway: 3–4"
Common tube sizes: 8", 10", 12", 14"
Standard rise: 7"
Standard run: 10–12"
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Your Concrete Estimate
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Cubic Yards
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Cubic Feet
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Cubic Meters
🛍️ Bags Needed (with waste factor)
For large pours (>1 yard) consider ordering ready-mix concrete. It's often cheaper and eliminates mixing labor.
💵 Cost Estimate
Cost per cubic yard of ready-mix: $
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Ready-mix typically costs $120–$200/yd³ + delivery. Adjust for your local market.
Standard Thickness Reference
| Application | Thickness | Notes |
|---|---|---|
| Sidewalk / Walkway | 3–4 inches | Residential use, no vehicle traffic |
| Patio / Backyard Slab | 4 inches | Standard residential outdoor slab |
| Driveway (passenger vehicles) | 5–6 inches | 6" recommended for long life |
| Driveway (heavy trucks) | 6–8 inches | Must include rebar or wire mesh |
| Garage Floor | 4–6 inches | Reinforce with fiber or rebar |
| Foundation Footing | 8–12 inches | Varies by load — consult engineer |
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Concrete Calculator FAQ
How many bags of concrete do I need for a 10×10 slab? +
A 10×10 ft slab at 4" thick = 12.3 cubic feet = 0.46 cubic yards. With 10% waste, you need about 0.5 yards. That's approximately 37 bags of 60lb concrete (0.45 cu ft/bag) or 28 bags of 80lb concrete (0.60 cu ft/bag). For this size, mixing bags is practical but time-consuming — consider a rented mixer or ordering a half-yard of ready-mix concrete.
How many cubic yards are in a concrete truck? +
A standard ready-mix concrete truck holds 8–10 cubic yards. Most concrete suppliers have a minimum order of 1 cubic yard. Short loads (under the truck's minimum) typically carry a surcharge of $50–$100 or more. For projects under 1 yard, pre-mixed bagged concrete is usually more economical despite the extra labor.
What's the difference between 60lb and 80lb bags? +
A 60lb bag of Quikrete covers approximately 0.45 cubic feet of concrete. An 80lb bag covers approximately 0.60 cubic feet. The 80lb bags are more economical per cubic foot but harder to handle. Many people prefer 60lb bags for DIY work since they're easier to lift and mix. Both produce concrete with similar strength (around 4,000 psi) when properly mixed.
Do I need rebar in a concrete slab? +
For slabs less than 4" thick (walkways), fiber reinforcement added to the mix is usually sufficient. For 4" residential patios and garage floors, wire mesh (6×6 #10 welded wire) is the minimum. For driveways, 4" slabs with #3 or #4 rebar at 18" on center is recommended. For anything structural (footings, foundations), consult a structural engineer — rebar size and spacing is code-dependent.
Why should I add 10% extra concrete? +
Concrete volume calculations are always estimates. Actual usage can exceed the calculation due to: uneven ground beneath the form (low spots use more concrete), slight variations in form dimensions, spills during pouring, and concrete that sticks to mixer blades or wheelbarrows. Running out mid-pour is a serious problem — concrete must be placed continuously. Always order or buy at least 10% extra. For complex shapes like steps or irregular footings, 15–20% is safer.
How long does concrete take to cure? +
Concrete gains strength continuously over time. General milestones: 24–48 hours — initial set, can walk on it carefully; 7 days — about 70% of design strength (can drive a passenger car); 28 days — reaches full design strength (4,000 psi for standard residential mix). Keep concrete moist for at least 7 days (curing) by covering with wet burlap, plastic sheeting, or applying a curing compound. Avoid freezing temperatures during the first 24 hours.