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
cu yd
Equivalent 80lb bags
88
Total cubic feet
48.0
Slab area
144
sq ft
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter slab thickness (in).
- 2Enter waste factor (%).
- 3Read your ready-mix needed on the right — it updates as you type.
- 4Hit Share to keep the scenario or send it to someone.
About this calculator
12x12 is a popular slab footprint for detached workshops, carports, and larger patios, landing at 144 square feet — 44% more area than a 10x10 pad, so the concrete volume scales accordingly. This calculator fixes the footprint at 12 feet by 12 feet and lets you dial in thickness and waste factor, since a 12x12 pad meant to carry a car or workshop equipment often gets poured at 5-6 inches with reinforcement rather than the 4-inch standard used for a simple patio. It returns both the ready-mix cubic yards to order from a batch plant and the 80lb bag equivalent for anyone hand-mixing a job this size, though at 144 square feet and 4+ inches thick, hand-mixing 90+ bags is a serious labor undertaking most people outsource to a delivered truck instead. The tool also shows raw cubic feet so you can cross-check your own measurements if your actual pad isn't a perfect 12x12 square.
Worked example
Using the values the calculator loads with:
Inputs
- Slab thickness: 4 in
- Waste factor: 10 %
Results
- Ready-mix needed: 1.96
- Equivalent 80lb bags: 88
- Total cubic feet: 48
- Slab area: 144
What each field means
Inputs
- Slab thickness (in)
- The slab thickness used in the calculation, measured in in. Starts at 4 in so you have a working example on load. Accepted range: 3–8 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: 0–25 %.
Results
- Ready-mix needed
- cu yd
- Equivalent 80lb bags
- Returned as a whole number. 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.
- Slab area
- sq ft
FAQ
How much concrete for a 12x12 slab at 4 inches?
About 1.78 cubic yards raw, or roughly 1.95-2.0 cubic yards with a standard 10% waste factor — most suppliers will round this to a 2 cubic yard order.
Is a 12x12 pad big enough for a workshop?
Yes, 144 square feet comfortably fits a single-car workshop or large storage building; if you plan to drive a vehicle onto it, budget for 5-6 inch thickness with wire mesh rather than the 4-inch patio standard.
How many bags of concrete for a 12x12 slab?
At 4 inches thick with 10% waste, roughly 105-110 bags of 80lb mix — a volume most contractors would rather order as delivered ready-mix instead of hand-mixing.
Does a 12x12 slab need a control joint?
Yes, a slab this size should have at least one control joint (often a center cross-cut) to control where cracking occurs as the concrete shrinks during curing.
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
10x10 Concrete Slab Calculator
Ready-mix yards and bag counts specifically for a 100 sq ft slab like a shed pad or patio.
20x20 Concrete Slab Calculator
Yardage for a full 400 sq ft slab — garage, large patio, or detached garage footing pad.
Concrete Cubic Yards Calculator
Convert a slab, footing, or pad's dimensions straight into cubic yards of ready-mix.
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/concrete-slab-12x12-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/concrete-slab-12x12-calculator" target="_blank" rel="noopener">12x12 Concrete Slab Calculator — RevenueLab</a> (2026).</p>
Source: [12x12 Concrete Slab Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/concrete-slab-12x12-calculator) (2026).