Construction · Editorial draft
How Much Concrete for a 10 × 12 Slab?
Concrete volume changes directly with thickness. Always convert inches to feet before multiplying footprint by depth.
Concrete volume changes directly with thickness. Always convert inches to feet before multiplying footprint by depth.
Use your own inputs in the tool ↗| Input | Example value |
|---|---|
| Length | 10 ft |
| Width | 12 ft |
| Thickness | 4 in |
| Extra material | 0 % |
| Bag yield | 0.6 ft³ |
- Volume
- 40
- Cubic yards
- 1.4815
- Bags
- 67
Thickness is the missing number
A 10 × 12-foot footprint gives 120 square feet, but not a concrete volume. A slab 4 inches thick and a slab 6 inches thick have the same footprint and different material quantities. Establish the required dimensions with an appropriate professional before estimating an order. This calculator does not specify reinforcement, foundation suitability or a structural mix design.
The four-inch example
Convert 4 inches to feet: 4 ÷ 12 = one-third of a foot. Multiply 10 × 12 × one-third to get 40 cubic feet. A cubic yard contains 27 cubic feet, so the volume is 40 ÷ 27 = 1.481481 cubic yards before any extra material. If an example bag yields 0.6 cubic feet, 40 ÷ 0.6 = 66.666667 bags. Round the purchase count upward to 67 whole bags.
Compare six inches and an allowance
At 6 inches, depth is half a foot. Volume becomes 60 cubic feet, or 2.222222 cubic yards, and the same assumed bag yield gives 100 bags. Thickness rose by 50%, so volume rose by 50%. With a 10% allowance on the four-inch example, volume becomes 44 cubic feet, or 1.629630 cubic yards; the assumed bag purchase becomes 74. The allowance is your planning input, not an engineering requirement.
Use the right measurement and yield
Enter length, width and slab thickness separately. The tool distinguishes feet for the footprint from inches for thickness in US mode; metric mode converts these input units. Do not enter four feet when you mean four inches. Check actual bag yield on the specific product: bag weight alone is not the same as yielded volume. A ready-mix order and a bag-based plan also have different practical handling requirements.
Keep the estimate in its lane
Irregular edges, sloped bases and changes in thickness can make a rectangular model incomplete. Break irregular geometry into appropriate measured pieces rather than treating this worked example as a site survey. Save the four-inch scenario before trying a different depth, then compare quantities using the same unit system. An exported estimate should retain the yield and allowance assumptions so another person can review them.
Common questions
Can this tell me the correct thickness? No. Can I order exactly the calculated number of yards? Confirm ordering increments, site conditions and delivery details with the supplier. Are bags interchangeable? No: use the documented yield for the product and mix instructions you plan to follow.
Sources and review notes
External technical reference checked; original arithmetic and implementation explanations remain subject to final editorial/browser review.
- NIST: SI conversion factors · checked 2026-10-09
Editorial approval and browser acceptance are pending. This unpublished draft does not claim measured business outcomes.
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