Choose a shape and enter its dimensions to calculate the concrete volume and how many pre-mixed bags you need.
Multiply the three dimensions of your pour (converted to feet) to get the volume in cubic feet, then divide by 27 to get cubic yards — the unit ready-mix trucks and bag counts are priced by. Example: a 10 ft x 10 ft slab poured 4 inches thick is 10 x 10 x (4/12) = 33.3 cubic feet, or about 1.23 cubic yards, which takes about 56 bags of 80 lb pre-mixed concrete.
Convert each dimension of your pour to feet, multiply length x width x thickness (slab), pi x radius^2 x height (cylinder), or width x length x depth (footing) to get cubic feet, then divide by 27 for cubic yards. Example: a 10 ft x 10 ft slab at 4 inches thick is 33.3 cubic feet, about 1.23 cubic yards, needing roughly 56 bags of 80 lb pre-mixed concrete.
1.23 cubic yards (0.94 m³) — 10 × 10 × (4/12) = 33.3 cubic feet, divided by 27.
56 bags — 1.23 cubic yards (33.3 cubic feet) divided by 0.60 cubic feet per bag, rounded up.
1.308 cubic yards — multiply cubic meters by 1.30795 to convert.
75 bags — 33.3 cubic feet divided by 0.45 cubic feet per 60 lb bag, rounded up. More bags than the 80 lb option since each bag yields less.
112 bags — 33.3 cubic feet divided by 0.30 cubic feet per 40 lb bag, rounded up.
About 0.94 cubic meters — multiply the 33.3 cubic feet by 0.0283168.
It increases the volume by 10% before rounding up bags — for the 1.23 cubic yard slab, that becomes 1.36 cubic yards and 62 bags of 80 lb instead of 56.
80 lb, 60 lb, and 40 lb bags are independent alternatives for the same total volume, not meant to be combined — pick whichever size is available or easiest to carry.
| Shape | Dimensions | Volume | 80 lb bags |
|---|---|---|---|
| Slab | 10 ft x 10 ft x 4 in | 1.23 yd3 (0.94 m3) | 56 |
| Slab, +10% margin | 10 ft x 10 ft x 4 in | 1.36 yd3 | 62 |
| Cylinder | 12 in dia x 3 ft, qty 6 | 0.52 yd3 (0.40 m3) | 24 |
| Footing | 16 in wide x 40 ft x 8 in deep | 1.32 yd3 (1.01 m3) | 60 |
| Slab (metric) | 3 m x 3 m x 10 cm | 1.18 yd3 (0.90 m3) | 53 |
Bags are sold as whole units, and running short mid-pour is far worse than having a partial bag left over, so the calculator always rounds the bag count up to the next whole bag after applying your chosen volume.
Extra margin is commonly recommended for uneven ground, spillage, or subgrade that soaks up more mix than a perfectly flat, prepared surface would. For a well-prepared, formed pour some builders skip it, but it is a safer default for DIY projects.
Yes. The three bag counts (80 lb, 60 lb, 40 lb) are independent alternatives calculated from the same total volume, not meant to be combined — pick whichever bag size is available or easiest for you to carry, and buy that count.
No. This calculator only estimates the concrete volume itself. Reinforcement (rebar, wire mesh) and a compacted gravel base are common additions to a real pour but are not included in the volume or bag count.
This calculator estimates volume from simple geometric shapes and standard published bag yields. Actual concrete needs can vary with subgrade unevenness, formwork leakage, and mix consistency, so treat the result as a planning estimate and consider rounding up further for irregular or uneven surfaces.
Last updated: 2026-08-17