How much concrete for a 10×10 slab?
For a 10-foot by 10-foot slab that is 4 inches thick, the exact volume is about 1.24 cubic yards. With 10% extra for uneven grade, spillage, and measurement variation, plan on approximately 1.36 cubic yards.
10 ft × 10 ft × 4 in
1.24 yd³ exact volume
The calculation
Convert the 4-inch depth to feet, multiply the three dimensions, then convert cubic feet to cubic yards:
A cubic yard contains 27 cubic feet. The final step adds a 10% planning allowance.
Concrete needed by slab thickness
Thickness changes the order quickly. These estimates include 10% extra and round bag quantities up to whole bags.
| Slab thickness | Concrete with 10% extra | 60-lb bags | 80-lb bags |
|---|---|---|---|
| 3 in | 1.02 yd³ | 62 | 46 |
| 4 in | 1.36 yd³ | 82 | 62 |
| 5 in | 1.70 yd³ | 102 | 77 |
| 6 in | 2.04 yd³ | 123 | 92 |
Bag estimates use approximate yields of 0.45 ft³ for a 60-lb bag and 0.60 ft³ for an 80-lb bag. Check the yield printed on the product you buy.
Ready-mix or bags?
At a 4-inch thickness, mixing more than 60 large bags is a substantial amount of handling. Ready-mix delivery can be more practical, but suppliers may have minimum-load or short-load charges. Ask the supplier about order increments, access for the truck, unloading time, and what happens to unused concrete.
If you use bags, divide the required cubic feet—including your extra allowance—by the bag’s listed yield, then round up. Do not rely on bag weight alone because different products can have different yields.
How much extra should you include?
The National Ready Mixed Concrete Association recommends allowing roughly 4% to 10% over plan dimensions for waste, over-excavation, and other contingencies. Ten percent is a sensible planning value for a small slab where a short order would interrupt the pour.
Extra concrete is not a substitute for measuring the forms after excavation. Recheck the finished length, width, and depth before ordering.
Before you order
- Confirm the slab design. Thickness, reinforcement, base preparation, joints, drainage, and concrete strength should suit the intended load and local requirements.
- Measure the inside of the forms. Use the actual finished dimensions rather than the planned dimensions.
- Check for thickened edges or footings. Calculate those volumes separately and add them.
- Confirm supplier details. Ask about mix requirements, delivery access, minimum orders, and the product’s bag yield.
Frequently asked questions
How many square feet is a 10×10 slab?
It covers 100 square feet. Square footage describes surface area; ordering concrete requires volume, so thickness must also be included.
How many 80-lb bags are needed?
At 4 inches thick, approximately 62 bags when using a 0.60-ft³ yield and 10% extra. Always use the yield stated on the bag.
Can I simply order 1.25 yards?
That is close to the exact geometric volume but leaves almost no allowance. A supplier can explain its ordering increments and help you choose an order quantity based on site conditions.