Concrete Calculator
Work out how much concrete you need for a slab, footing, wall or round column: cubic yards, bags and material cost, with waste included. Then download or print a clean summary.
- Cubic yards & feet
- 40, 60 & 80 lb bags
- PDF summary
Your pour
Pick the shape, enter its size, and add a waste allowance.
Pricing the labor too? Find your true hourly cost with the employee cost calculator.
Your concrete
Updates as you type. Includes your waste allowance.
How to Calculate Concrete
Concrete is ordered by volume, almost always in cubic yards. To work out how much you need, find the volume of the space in cubic feet, convert it to cubic yards, then add a waste allowance. The calculator above does this for you, but here is the math so you can check any quote.
Concrete Volume Formulas
For a wall, use the wall's height in place of width. Dividing the thickness by 12 converts inches to feet, and dividing by 27 converts cubic feet to cubic yards, because there are 27 cubic feet in a cubic yard.
Worked Example: a 12 × 12 ft Patio Slab
A 12 × 12 ft patio slab poured 4 inches thick, with a 10% waste allowance:
Ready-mix is usually ordered in quarter-yard steps, so 1.96 cubic yards rounds up to 2 cubic yards.
How Many Bags of Concrete Do You Need?
Bagged concrete mix is sold by weight but used by volume. Standard concrete mix yields roughly the following per bag, so one cubic yard (27 cubic feet) takes:
| Bag size | Yield per bag | Bags per cubic yard |
|---|---|---|
| 80 lb | 0.60 cu ft | 45 |
| 60 lb | 0.45 cu ft | 60 |
| 40 lb | 0.30 cu ft | 90 |
Yields can vary slightly between products, so check the bag. Because a single yard takes 45 heavy bags, many contractors use bags for small jobs (post holes, small pads, repairs) and switch to ready-mix delivery for larger pours. If you order ready-mix, check the supplier's minimum order and any short-load fee.
How Much Waste Should You Add?
- 5% for simple forms on a well-prepared, level base
- 10% for most slabs, footings and walls
- 15% for uneven ground, irregular shapes or hard-to-reach pours
Running short in the middle of a pour can mean a cold joint and a second delivery fee. A little extra concrete is almost always cheaper than not enough.
From Concrete Quantity to a Profitable Quote
The concrete itself is only part of the price. A complete concrete estimate also covers excavation and base material, forms, reinforcement (rebar or mesh), finishing labor, pump or equipment rental, delivery fees, overhead and profit. Price the labor at its true cost, then add overhead and a margin on purpose:
- Find your real hourly labor cost with the employee cost calculator
- Set your price with the markup calculator or margin calculator
- Put it all together in a free construction estimate template