The formula behind every concrete estimate
Concrete volume comes down to one calculation: length × width × depth. The tricky part is unit conversion — concrete is sold by the cubic yard in the US, but most people measure in feet and inches.
For a slab, that means converting depth from inches to feet (divide by 12) before multiplying, then dividing the total cubic feet by 27 to get cubic yards. A calculator handles this automatically, but knowing the formula helps you sanity-check the result.
Always add a waste allowance
No pour is perfectly efficient — subgrade isn't perfectly level, forms shift slightly, and some concrete is lost to spillage. Contractors typically add 5–10% extra to the calculated volume, and more (10–15%) for irregular shapes like curved walkways or footings with uneven excavation.
| Job type | Recommended waste |
|---|---|
| Flat rectangular slab | 5% |
| Footings & foundations | 10% |
| Curved or irregular pours | 10–15% |
How to estimate with DailyToolsAI
Enter your dimensions
Length, width, and depth (or diameter for round footings and posts).
Get volume instantly
The Concrete Calculator converts to cubic yards and shows bag counts for pre-mix bags too.
Add your waste margin
Round up by 5–10% before placing your order.
Ready-mix trucks often have a minimum load and a short-load fee below a certain volume (commonly around 1 cubic yard). For small jobs, bagged concrete mix can work out cheaper even though the per-yard cost looks higher.
Don't forget sub-base and reinforcement
Concrete volume only covers the pour itself. Most slabs also need a compacted gravel sub-base (typically 4 inches) and, depending on load requirements, rebar or wire mesh reinforcement — factor both into your budget and timeline separately from the concrete estimate.
Calculate your concrete volume
Free, instant, and works for slabs, footings and posts.