Thickness comparison
4-Inch vs. 6-Inch Concrete Slab
Last reviewed September 4, 2026
At the same length and width, a 6-inch slab uses exactly 50% more concrete than a 4-inch slab. Complete installed price does not rise by exactly 50%, because preparation, forms, mobilization, and finishing do not scale in the same way. Use the thickness specified for the project.
Use the related calculator →Reference table
Concrete volume before allowance
Geometric volume only; add a visible allowance before ordering.
| Slab area | 4 in slab | 6 in slab | Volume difference |
|---|---|---|---|
| 100 ft² | 1.23 yd³ | 1.85 yd³ | +50% |
| 200 ft² | 2.47 yd³ | 3.70 yd³ | +50% |
| 400 ft² | 4.94 yd³ | 7.41 yd³ | +50% |
01
Why the material difference is exactly 50%
For a fixed area, volume changes in direct proportion to thickness. Six inches divided by four inches is 1.5, so the concrete quantity is 50% higher. Per 100 ft², that is about 56 nominal 80 lb bags at 4 inches and 84 at 6 inches, before allowance and whole-bag rounding.
- The length and width must remain the same.
- Thickened edges and footings should be calculated separately.
- Supplier rounding comes after the geometric comparison.
02
What changes in the budget
Concrete quantity changes directly. Excavation, haul-off, base quantity, and reinforcement may also change, but not automatically or at the same rate.
03
What thickness does not solve
Thickness alone does not guarantee performance. Base support, drainage, loading, reinforcement, joint layout, curing, and site conditions remain part of the project system.
- Do not use this quantity page to choose a structural thickness.
- Do not treat patios, floors, driveways, and supported slabs as interchangeable.
- Compare contractor quotes only after matching their complete scopes.
Limits
What this comparison does not decide
- This is a quantity and planning-cost comparison, not a thickness recommendation.
- Local requirements and project documents override examples.
- Bag counts use nominal yield and exclude allowance.
Common questions
4-Inch vs. 6-Inch Concrete Slab FAQ
How much more concrete does a 6-inch slab use?
Exactly 50% more than a 4-inch slab with the same area.
Does a 6-inch slab cost 50% more?
The concrete quantity does. Complete installed cost usually does not scale one-for-one because several costs are fixed or nonlinear.
How many cubic yards cover 100 square feet?
About 1.23 yd³ at 4 inches or 1.85 yd³ at 6 inches, before allowance.
Can I choose slab thickness from this table?
No. Use the thickness specified by the project design and applicable requirements.