Concrete Calculator
Calculate concrete for slabs, footings, walls, columns, and sonotubes. Add pours to get total cubic yards, the number of 40/60/80 lb bags, a waste allowance, and ready-mix cost. Free, no sign-up.
What to calculate next
Tools commonly used alongside this calculation
Rebar Weight Calculator
Calculate rebar weight from ASTM A615 bar sizes. Add bars by size, length, and quantity to get the total weight in pounds and tons, plus a per-bar breakdown and optional cost. Free, no sign-up.
Concrete Block (CMU) Calculator
Estimate a CMU wall from its size: block count, mortar (cement + sand), core-fill grout, and rebar for 6, 8, and 12 in units per NCMA TEK 14-13. Subtract openings and add a waste allowance. Free, no sign-up.
Joist Span Calculator
Find the maximum allowable floor or deck joist span from the IRC span tables. Pick species, grade, size, and spacing to get the code max span by joist size and check it against the span you need. Free, no sign-up.
Explanation
Concrete is ordered and priced by volume, so the first question on any pour is “how much concrete do I need?” This calculator finds the volume of slabs, footings, walls, columns, and sonotubes, adds them up across as many pours as you have, and converts the total to cubic yards and to the number of 40, 60, or 80 lb pre-mix bags — with a waste allowance and an optional ready-mix cost.
How to calculate concrete volume
Every shape comes down to converting the dimensions to feet, multiplying for the volume in cubic feet, then dividing by 27 to get cubic yards (there are 27 ft³ in one yd³):
| Shape | Dimensions | Volume (ft³) |
|---|---|---|
| Slab / footing | length L, width W (ft); thickness T (in) | L × W × (T ÷ 12) |
| Wall | length L, height H (ft); thickness T (in) | L × H × (T ÷ 12) |
| Column / Sonotube | diameter D (in); height H (ft) | π × (D ÷ 24)² × H |
Lengths and heights are entered in feet and thickness or diameter in inches, matching how slabs and sonotubes are specified. A 10 ft × 10 ft × 4-inch slab is 33.3 ft³, or about 1.23 cubic yards before waste.
Bags vs. ready-mix
For small pours you buy pre-mixed concrete in bags; for larger ones you order ready-mix by the cubic yard. The number of bags is the volume divided by how much each bag yields once mixed. Bagged concrete usually stops making sense above roughly 1 to 2 cubic yards, where the bag count and mixing labor outweigh a ready-mix delivery.
| Bag size | Yield (ft³) | Bags per yd³ |
|---|---|---|
| 80 lb | 0.60 | 45 |
| 60 lb | 0.45 | 60 |
| 40 lb | 0.30 | 90 |
An 80 lb bag is the most economical per cubic foot and means fewer bags to mix, while a 60 or 40 lb bag is easier to lift. The calculator rounds the bag count up, because you cannot buy a partial bag.
Waste, reinforcing, and limitations
Always order a little extra. A 5–10% waste allowance covers spillage, an uneven subgrade, and slight over-excavation, and rounding up before you order keeps you from running short mid-pour. This tool estimates concrete volume only — it does not size footings for your frost line or loads, and it does not include the reinforcing steel. For the rebar inside a reinforced-concrete pour, use the rebar weight calculator. Confirm structural dimensions and footing depths against your local code and a licensed engineer.