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Free concrete calculator
Cubic yards and bag counts for any slab. Free, no signup.
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Enter your numbers and watch the results update live.
Related definitions
Concrete is ordered by the cubic yard and mixed by the bag — this calculator gives you both. Enter the slab's length, width, and depth in inches; get cubic yards for ready-mix orders plus 80-lb and 60-lb bag counts for smaller pours.
The formula, in plain English
Cubic feet = length × width × (depth ÷ 12). Cubic yards = cubic feet ÷ 27. Bag counts divide the cubic feet by each bag's yield: 0.6 cu ft per 80-lb bag, 0.45 cu ft per 60-lb bag.
Worked example
A 10 × 10 ft patio, 4 inches thick: cubic feet = 10 × 10 × (4 ÷ 12) = 33.33. Cubic yards = 1.23. Bags: 56 eighty-pounders or 74 sixty-pounders. Add 5–10% for waste before ordering.
Tips
- Order 5–10% extra. Spillage, uneven subgrade, and form spread eat concrete — a short load mid-pour is far more expensive than a little waste.
- Bags are for small jobs. Past about a cubic yard, ready-mix delivery is usually cheaper than bags and far less labor.
- Depth matters most. Length and width are easy to measure; depth is where estimates go wrong. Probe the subgrade in several spots.
Also free
paint cost calculator, roofing cost calculator, markup calculator — and the free invoice generator when it is time to bill.
Frequently asked questions
How many bags make a cubic yard?
About 45 eighty-lb bags or 60 sixty-lb bags per cubic yard — this calculator does the exact division for your slab's volume.
80-lb vs 60-lb bags — which should I buy?
Same concrete, different lifting. Eighty-pound bags mean fewer bags to mix and carry; sixty-pound bags are kinder to backs on DIY jobs.
Should I add extra for waste?
Yes — 5–10% over the calculated volume is standard for spillage and uneven subgrade. The calculator gives the exact figure; you add the waste factor when ordering.
Is this calculator really free?
Yes. Unlimited calculations, no signup, no watermark, no catch — like all of Billia's free tools.
Turn the number into an invoice
Ran the numbers? Bill it with Billia's free invoice generator — no signup, no watermark.