Calculator
Formula Used
Base slab volume: Length × Width × Slab Thickness
Extra edge depth: Total Edge Depth − Slab Thickness
Partial edge volume: Selected Edge Length × Edge Width × Extra Edge Depth
Full perimeter edge volume: [Outer Area − Inner Area] × Extra Edge Depth
Order volume: [Base Volume + Edge Volume] × [1 + Waste Percent ÷ 100]
Cubic yards: Cubic Feet ÷ 27
Metric volume: Cubic Feet × 0.0283168466
Weight: Cubic Meters × Concrete Density
Estimated cost: Concrete Cost + Rebar Cost
How To Use This Calculator
Enter the outside slab length and width. Choose the same unit for all length fields. Add the regular slab thickness, thickened edge width, and total edge depth. Select how many long and short sides have thickened edges. Enter waste, material cost, density, bag yield, and reinforcement details. Press calculate. Then download the result as CSV or PDF when needed.
Example Data Table
| Slab Size | Slab Thickness | Edge Width | Edge Depth | Edges | Waste | Approx Order |
|---|---|---|---|---|---|---|
| 12 ft × 10 ft | 4 in | 12 in | 12 in | Full perimeter | 5% | 2.59 cu yd |
| 20 ft × 16 ft | 5 in | 14 in | 14 in | Full perimeter | 7% | 7.10 cu yd |
| 18 ft × 10 ft | 4 in | 12 in | 10 in | Two long sides | 8% | 3.36 cu yd |
Thickened Edge Concrete Planning
A thickened edge slab adds deeper concrete around selected sides. It supports heavier wall lines. It also helps the slab act like a shallow footing. This calculator separates the regular slab volume from the extra edge volume. That makes the estimate easier to check before ordering ready mix.
Why Edge Volume Matters
Small depth changes can add many cubic yards on large slabs. The edge width, edge depth, selected sides, and waste factor all affect the final order. A full perimeter edge is handled as a ring. This avoids counting the corner areas twice. Partial edge layouts use a clear linear method, which is useful for porches, garages, pads, and equipment slabs.
Advanced Material Checks
The tool also estimates concrete weight, delivery cost, bag quantity, and reinforcing length. These numbers help compare ready mix and bagged concrete. They also help with hauling limits, form planning, and budget review. Rebar is estimated from slab grid spacing plus extra bars running along the thickened edge.
Good Field Practice
Always confirm dimensions before excavation. Measure the outside slab length and width. Then check the planned slab thickness, edge depth, and edge width. Keep units consistent inside the form. Use a waste factor for spills, grade changes, and uneven subbase. Many jobs use five to ten percent, but rough soil may need more.
Using The Result
The cubic yard result is normally the ready mix order number. The cubic meter result helps metric projects. The weight estimate helps with transport and site access. The cost estimate is only as good as the local price entered. The PDF and CSV buttons save the same calculation for records, quotes, and field checks.
Important Limits
This calculator is a quantity tool. It is not a structural design. Soil bearing, reinforcement, frost depth, drainage, and code rules can change the required section. For load bearing buildings, ask a qualified professional to verify the slab edge design before construction starts.
Estimating Workflow
Start with the clean plan dimensions. Enter conservative field measurements when plans are unclear. Review the base slab and edge add-on separately. Then check the waste-adjusted order. Save the file before calling suppliers, so each quoted price matches the same quantity and schedule.
FAQs
What is a thickened edge slab?
It is a concrete slab with deeper concrete near one or more edges. The deeper part can help support walls, posts, or heavier edge loads.
Does this calculator replace structural design?
No. It estimates concrete quantity, weight, cost, and basic rebar length. A qualified designer should verify soil, load, frost, and code requirements.
Why is the full perimeter method different?
A full perimeter edge forms a ring. The calculator subtracts the inner area from the outer area. This avoids counting corner volume twice.
What waste percent should I use?
Many jobs use five to ten percent. Use more for uneven subgrade, complex forms, hand placement, or uncertain field dimensions.
Can I use metric dimensions?
Yes. Select meters as the input unit. The calculator converts values internally and still reports cubic feet, cubic yards, and cubic meters.
How is concrete weight calculated?
The calculator converts order volume to cubic meters. It then multiplies by the concrete density entered in kilograms per cubic meter.
How is rebar length estimated?
Grid bars are estimated from slab length, width, and spacing. Edge bars are estimated from selected edge length and the number of edge runs.
Why are local prices needed?
Concrete and rebar prices vary by supplier, load size, region, and delivery fees. Entering local prices gives a more useful estimate.