Monolithic Slab Calculator
Estimate concrete for a monolithic slab (thickened-edge slab) including the slab area, footing perimeter, and total volume.
What Is a Monolithic Slab?
A single-pour foundation with integrated footings
A monolithic slab (also called a "thickened-edge slab") is a concrete foundation where the slab and footing are poured at the same time. The perimeter edges are thickened to serve as footings, while the interior is a standard 4-6 inch slab.
Key Components:
- Slab area: Standard 4-6" thickness across the interior
- Thickened edge (footing): 12-24" deep along the perimeter
- Perimeter beam: Typically 12" wide at the base, tapering to slab thickness
- Reinforcement: Rebar in the footing and wire mesh in the slab field
How to Calculate Monolithic Slab Concrete
Step 1 — Slab Volume:
Slab (cu ft) = Length × Width × (Slab Thickness ÷ 12)
Step 2 — Footing Volume:
Perimeter = 2 × (Length + Width)
Footing (cu ft) = Perimeter × Footing Width × (Footing Depth ÷ 12)
(Subtract the slab portion already counted above)
Step 3 — Total:
Total (cu yd) = (Slab + Footing) ÷ 27 × 1.10 (waste)
Example: 30×40 Monolithic Slab
Slab: 4" thick, Footing: 12" wide × 12" deep
Slab: 30 × 40 × (4÷12) = 400 cu ft = 14.81 yd³
Footing: 140 ft perimeter × 1 ft × (12÷12) = 140 cu ft = 5.19 yd³
Overlap credit: 140 ft × 1 ft × (4÷12) = -46.67 cu ft = -1.73 yd³
Net footing: 5.19 - 1.73 = 3.46 yd³
Total: (14.81 + 3.46) × 1.10 = 20.10 yd³
Common Monolithic Slab Sizes
Slab: 4" thick, Footing: 12" wide × 12" deep
| Size | Slab (yd³) | Footing (yd³) | Total w/ 10% | Est. Cost |
|---|---|---|---|---|
| 20×30 | 7.41 | 2.47 | 10.87 | $1,300-$1,900 |
| 24×36 | 10.67 | 3.16 | 15.21 | $1,800-$2,700 |
| 30×40 | 14.81 | 3.46 | 20.10 | $2,400-$3,600 |
| 30×50 | 18.52 | 3.83 | 24.59 | $2,900-$4,400 |
| 40×60 | 29.63 | 5.19 | 38.30 | $4,600-$6,900 |
Structural Engineering Required
Monolithic slabs are structural foundations. The footing dimensions, rebar placement, and concrete strength must be designed by a licensed engineer and comply with local building codes. This calculator provides estimates only — always have your design verified by a professional.
When to Use a Monolithic Slab
Good For
- • Garages and workshops
- • Pole barns and metal buildings
- • Single-story homes on level ground
- • Areas with stable, well-draining soil
- • Warm climates (no deep frost line)
Avoid When
- • Sloped or uneven terrain
- • Expansive clay soils
- • Deep frost line areas (without modification)
- • Multi-story structures
- • Heavy loads beyond residential
Need a Standard Slab Calculator?
For non-monolithic slabs, use our standard slab calculator for volume and bag estimates.