Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Ready-mix needed
1.96
80-lb bags (DIY mix)
88
Estimated concrete cost
$293
Total cubic feet
48.0
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How to use this
- 1Enter slab length (ft).
- 2Enter slab width (ft).
- 3Enter thickness (in).
- 4Enter waste factor (%).
- 5Enter ready-mix price per cubic yard ($).
- 6Read your ready-mix needed on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
12x12 is a common footprint for a backyard patio slab or a standalone shed pad — big enough to be useful, small enough to pour in a weekend. This tool defaults to 12 feet by 12 feet at 4 inches thick, then converts that volume into ready-mix cubic yards, an equivalent 80-lb bag count for a hand-mixed pour, and a total dollar estimate so you can compare a delivery quote against DIY bags before committing.
Worked example
Using the values the calculator loads with:
Inputs
- Slab length: 12 ft
- Slab width: 12 ft
- Thickness: 4 in
- Waste factor: 10 %
- Ready-mix price per cubic yard: 150 $
Results
- Ready-mix needed: 1.96
- 80-lb bags (DIY mix): 88
- Estimated concrete cost: $293
- Total cubic feet: 48
What each field means
Inputs
- Slab length (ft)
- The slab length used in the calculation, measured in ft. Starts at 12 ft so you have a working example on load.
- Slab width (ft)
- The slab width used in the calculation, measured in ft. Starts at 12 ft so you have a working example on load.
- Thickness (in)
- The thickness used in the calculation, measured in in. Starts at 4 in so you have a working example on load. Accepted range: 2–12 in.
- Waste factor (%)
- The waste factor used in the calculation, measured in %. Starts at 10 % so you have a working example on load. Accepted range: 0–30 %.
- Ready-mix price per cubic yard ($)
- The ready-mix price per cubic yard used in the calculation, measured in $. Starts at 150 $ so you have a working example on load.
Results
- Ready-mix needed
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- 80-lb bags (DIY mix)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Estimated concrete cost
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total cubic feet
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How many cubic yards for a 12x12 slab at 4 inches?
About 1.95 cubic yards with a 10% waste factor included — most concrete plants round that to a 2-yard minimum load.
Do I need rebar or mesh in a 12x12 slab?
Wire mesh or rebar on a grid is standard for crack control on any slab over 100 square feet, and 12x12 (144 sq ft) qualifies.
What's the difference between a 12x12 slab and patio pavers?
A poured slab is one continuous surface that resists weed growth and shifting, while pavers are individually replaceable but require a compacted base and edging. Slabs are usually cheaper per square foot for a simple rectangle.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). 12x12 Concrete Slab Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/12x12-concrete-slab-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/12x12-concrete-slab-calculator" target="_blank" rel="noopener">12x12 Concrete Slab Calculator — RevenueLab</a> (2026).</p>
Source: [12x12 Concrete Slab Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/12x12-concrete-slab-calculator) (2026).