Estimate cubic yards and bag counts for slabs, footings, columns, and post holes—before the truck arrives or the bags hit your cart.
Example values shown — enter your project measurements.
See results ↓Convert every measurement to feet first. For round columns and post holes, the calculator uses π × radius² × height, then converts cubic feet to cubic yards.
One cubic yard equals 27 cubic feet. Bag estimates use typical cured yields: 0.30 ft³ for 40 lb, 0.45 ft³ for 60 lb, and 0.60 ft³ for 80 lb. Always check the yield printed on your mix.
The cheapest option is not always the easiest one. Match the delivery method to the volume, access, crew, and speed of your pour.
Usually the practical choice around 1 cubic yard or more.
Often simpler below about ½ cubic yard.
Quick estimates for a 4-inch-thick slab. The order amount includes the calculator’s recommended 10% waste allowance.
| Slab size | Base volume | Order with 10% | 80 lb bags |
|---|---|---|---|
| 8 × 10 ft | 0.99 yd³ | 1.09 yd³ | 49 |
| 10 × 10 ft | 1.23 yd³ | 1.36 yd³ | 62 |
| 12 × 20 ft | 2.96 yd³ | 3.26 yd³ | 147 |
| 16 × 20 ft | 3.95 yd³ | 4.35 yd³ | 196 |
| 20 × 20 ft | 4.94 yd³ | 5.43 yd³ | 245 |
Bag counts are rounded up and assume 0.60 cubic feet of yield per 80 lb bag. A supplier may round a ready-mix order to its accepted increment.
A full cubic yard is a lot of hand mixing. These standard estimates use typical package yields; moisture, compaction, and product formulation can change the real yield.
About 0.30 ft³ per bag.
About 0.45 ft³ per bag.
About 0.60 ft³ per bag.
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Divide cubic feet by 27, because one cubic yard contains 27 cubic feet. A 10 × 10 ft slab at 4 inches thick is about 33.33 cubic feet, or 1.23 cubic yards before waste.
Plan on about 90 forty-pound bags, 60 sixty-pound bags, or 45 eighty-pound bags per cubic yard. Those counts assume typical yields of 0.30, 0.45, and 0.60 cubic feet, so verify the package label before buying.
Ten percent is a useful default for most small projects because the ground is rarely perfectly level and some mix is lost during handling. For a precisely formed indoor pour, 5% may be enough; irregular excavation can justify 10–15%.
Four inches is common for patios, walkways, and many residential floors. Driveways and areas carrying heavier loads may need 5–6 inches or an engineered design; local soil, reinforcement, and code requirements matter.
Yes, but fresh concrete must be protected from freezing. If air temperatures are near or below 40°F, use a cold-weather mix plan, warm materials as needed, and insulating blankets; never pour onto frozen ground.
Use a prepared spare form for stepping stones, equipment pads, or small landscape blocks before the mix begins to set. Do not wash wet concrete or cement slurry into storm drains, soil, or waterways; let leftovers harden and follow local disposal rules.