Thickness dominates
A slab at 6 in needs 50% more concrete than the same slab at 4 in — depth is a linear multiplier on volume.
concrete calculator
Concrete Calculator
Estimate how much concrete you need for a slab, footing, wall, column, stairs, or curb. Enter the shape and dimensions, and this calculator returns the volume in cubic yards plus the number of 60-lb and 80-lb bags — with a waste allowance you control and every step of the math shown.
Quick answer
A 10×10 ft slab at 4 in needs ~1.23 cu yd of concrete before waste — order ~1.36 cu yd (≈ 62 bags of 80-lb) with 10% waste.
You order: 1.36 cubic yardsStandard industry factors
Enter your project
Build your estimate
Start with a preset
Live result
1.36 cubic yards
What you order
- Concrete volume1.23 cu yd
- Waste allowance (10%)+0.12 cu yd
- Order this much (ready-mix)1.36 cu yd
- Or 80-lb bags62 bags
- Or 60-lb bags82 bags
Standard industry factors · confirm with your supplier
The model, unpacked
Scenario breakdown
10 × 10 ft slab at 4 in
Concrete volume
1.23 cu yd
Waste allowance (10%)
+0.12 cu yd
Order this much (ready-mix)
1.36 cu yd
Or 80-lb bags
62 bags
Or 60-lb bags
82 bags
You may also need
Materials for the same job
Planning a full project? Most jobs use more than one material. You will often pair gravel, paver base and sand with concrete on the same site.
Interpret the output
What makes this move?
A trustworthy estimate explains the levers behind the number. These are the factors that change how much you need to order.
Shape matters
Round columns use πr², so a 12-in column holds far less concrete than a 12-in-square form of the same height.
Bags vs ready-mix
Under about 1 cubic yard, bags are practical. Above it, ready-mix is cheaper per yard and avoids mixing 60+ bags by hand.
FAQ
Common questions
Straight answers about quantities, conversions, and how much to order — no lead-gen fog.
45 — each 80-lb bag yields about 0.60 cu ft, and 27 ÷ 0.60 = 45. A 60-lb bag yields about 0.45 cu ft, so 60 per cubic yard.