Concrete Slab Calculator
Estimate how much concrete and how many bags you’ll need for your slab or foundation.
This is an estimate. Your actual needs may vary based on site conditions.
(Estimate only—add 5–10% for waste; actual needs may vary by site conditions.)
Start with a Strong Foundation
Why Your Concrete Slab Matters
A well-poured concrete slab is the base of any durable garage or metal building. It keeps your structure stable, square, and protected from moisture.
Local codes often recommend 4–6 in of thickness. When ordering, add 5–10% extra concrete to account for waste and edge variation.
How to Measure Concrete
Calculate slab volume in cubic yards (yd³) with this formula.
Measure The Square Footage
Multiply Length × Width to get area in sq ft.
Area (sq ft) = Length ft × Width ft
Example: 25 ft × 25 ft = 625 sq ft
Convert Thickness (in → ft)
Divide inches by 12 to use feet in the formula.
Thickness (ft) = Thickness (in) ÷ 12
Example: 4 in ÷ 12 = 0.333 ft
Get Volume in Cubic Feet
Multiply area by thickness (in feet).
Volume (ft³) = Area sq ft × Thickness ft
Example: 625 × 0.333 = 208.3 ft³
Convert Cubic Feet to Yards
Divide by 27 (ft³ per yd³).
Volume (yd³) = ft³ ÷ 27
Example: 208.3 ÷ 27 = 7.71 yd³
Estimate Bag Counts
Approximate premixed bags per cubic yard:
- 90 × 40-lb bags = 1 yd³
- 60 × 60-lb bags = 1 yd³
- 45 × 80-lb bags = 1 yd³
Next Step:
Build on Your Slab
Add walls, doors, and layout with instant pricing.
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Frequently Asked Questions
It depends on your project size! Bagged concrete is great for small DIY jobs since you can mix as you go. But if you’re pouring a large slab, ready-mix concrete is easier and faster—plus, it saves you a lot of labor.
If you’re unsure, check out our how to pour a concrete slab guide for tips!
A cubic yard of concrete is about 45 80-pound bags of concrete mix. If you’re using smaller or larger bags, the total will vary. A good trick is to calculate how much you need before you start so you don’t have to make multiple trips to the store!
Concrete prices vary, but ready-mix concrete typically runs $125 to $185 per yard if you’re doing it yourself. If you hire a contractor, they may charge $4 to $7 per square foot to pour the slab. Prices will vary depending on location and project size, so always get a few quotes!
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