This model keeps the uniform slab and thickened border separate. Steps, piers, seat walls, curves and grade beams should be calculated as additional shapes.
01 / Formula
How this is calculated
Volume = slab area × thickness + perimeter × border width × extra border depth02 / Assumptions
What the estimate assumes
- ✓The patio is rectangular.
- ✓The border follows the full perimeter.
- ✓Border depth is entered as additional depth below the main slab.
03 / Worked example
See the math in context
A 20 × 16 ft patio has 320 sq ft of main slab area; a 12-inch-wide perimeter border adds 72 sq ft at the extra depth.
04 / Guidance
Avoid double-counting the border
The main slab calculation already includes its normal thickness beneath the border. Enter only the border’s additional depth.
Questions
Frequently asked
Should I order exactly the calculated amount?+
Usually no. Excavation variation, form dimensions, spillage, and uneven subgrade can increase actual volume. Use the editable waste allowance and discuss minimum loads and order increments with the supplier.
How many cubic feet are in a cubic yard?+
There are exactly 27 cubic feet in one cubic yard. Divide cubic feet by 27 to convert to cubic yards.
Does this replace a structural design?+
No. These tools estimate material quantity only. A qualified professional and applicable plans, codes, site conditions, reinforcement requirements, and manufacturer instructions govern the project.
Sources