Cubic yards, cubic feet, and bag count
How Much Concrete Do I Need
Answer first: Enter your length, width, and thickness. Get cubic yards, cubic feet, bag count, and cost estimate in seconds.
10 × 10 ft, 4 in thick slab
1.23 yd³ — about 56 bags
With 10% waste. Divide cubic feet by 27 to get cubic yards.
12 × 20 ft driveway, 4 in
2.96 yd³ — ready-mix territory
Above 1–2 yd³, ready-mix delivery is usually cheaper than bags.
How Much Concrete Do I Need?
Enter dimensions. Get cubic yards, bags, and cost instantly.
Cubic yards
1.36
Cubic feet
36.7
80 lb bags
62
Bag cost est.
$310
Interactive workflow
Run the numbers, then save or export the project
The formula: how much concrete you need
Volume (ft³) = Length × Width × (Thickness ÷ 12). Divide by 27 for cubic yards. Add 10% waste.
| Benchmark says | Replace with local input | Next check |
|---|---|---|
| Formula without waste | Always add 5–15% waste. For a clean formed slab use 5–10%. For uneven ground use 15%. | Use 10% as the default — adjust up for complex shapes. |
| Only cubic yards | Ready-mix plants quote in yd³. Hardware stores sell bags by count. | The calculator above shows both — use whichever matches your purchase path. |
| No cost check | Bag cost vs ready-mix delivery depends on volume and local pricing. | Enter your local prices to see which option costs less. |
Concrete quantity checklist
Steps before placing your concrete order.
| Signal to check | What it means | Next step |
|---|---|---|
| Measure twice | Length, width, and thickness are measured at the actual site. | Add 2 in to width and length for small overruns on forms. |
| Waste factor | Added 5–15% waste depending on pour complexity. | 10% is a safe default for most residential pours. |
| Buying path | Decided between ready-mix delivery and bagged concrete. | Above ~1–2 yd³, ready-mix is usually cheaper. Below that, bags may win. |
| Confirmed volume | You have a yd³ number ready for the ready-mix plant. | Round up to the nearest 0.25 yd³ to avoid running short. |
Related concrete planning tools
Move from a single calculation into a purchase, proposal, or pour-day decision with connected calculators and checklists.
How much concrete do I need for a 10×10 slab?
A 10×10 ft slab at 4 inches thick needs about 1.23 cubic yards (33.3 ft³) with 10% waste. That's about 56 bags of 80 lb concrete.
How do I calculate cubic yards of concrete?
Multiply length × width × (thickness ÷ 12) to get cubic feet, then divide by 27. Formula: yd³ = (L × W × T) ÷ 27. Add 5–15% for waste.
How much does a yard of concrete cover?
One cubic yard covers 81 sq ft at 4 inches thick, or 108 sq ft at 3 inches thick. Use the calculator above to get exact coverage for your dimensions.
How many 80 lb bags of concrete make a yard?
About 45 bags of 80 lb (0.6 ft³ each) make one cubic yard. For 60 lb bags (0.45 ft³ each), you need about 60 bags per yard.
Should I order ready-mix or buy bags?
For pours under 1 cubic yard, bags from a hardware store can be cheaper. Above 1–2 yards, ready-mix delivery usually wins on cost per yard. The calculator compares both.
Planning disclaimer
Calculations include a standard waste factor. Actual concrete needed may vary based on site conditions, form accuracy, and pour technique. Order from your concrete supplier based on a confirmed site measurement.