Concrete slab thickness guide
Use this calculator for a flat rectangular concrete slab: a patio, driveway, sidewalk, garage floor, or shed pad. Enter the finished length, width, and the thickness specified for the project. The tool accepts separate units because plan dimensions are often in feet while thickness is commonly given in inches.
Worked example, waste guidance, and a pre-order checklist.
Use the project thickness, not a guess
A 4-inch slab is common for many light-duty patios and walkways, but it is not a universal recommendation. Driveways, garage floors, heavy equipment pads, and structural work may need a different thickness, reinforcement, base, or edge detail. Check the project plan and local requirements before ordering.
Measure thickened edges separately
If the slab has a turned-down edge, grade beam, curb, steps, or isolated thickened sections, calculate those volumes separately from the main slab. Treating every part as one uniform thickness can understate the concrete required.
How much slab waste should I add?
The 5% default is a useful starting point for a simple rectangular pour on a prepared base. Increase it for irregular borders, uneven subgrade, hand-formed edges, or any condition likely to use more material than the drawing suggests.
Example slab projects
A small patio, shed pad, or walkway landing.
A common driveway slab with a modest waste allowance.
A larger slab where ready-mix delivery is usually more practical.
Slab calculator FAQ
Can I use feet for length and inches for thickness?
Yes. Select the unit beside each dimension. This is useful for a patio or concrete pad measured in feet with a thickness measured in inches.
Does this calculator include reinforcing steel or base material?
No. It estimates concrete volume, bags, waste, and example material costs only. Reinforcement, gravel base, forms, delivery, and finishing are separate project requirements.