Concrete Slab & Subgrade Calculator with Visual Cross-Section
Calculate concrete volume and subgrade material requirements (gravel/sand) including compaction factors. Generates a visual layer diagram.
Dimensions
Layers
| Layer | Compact Vol | Order Vol | Weight (Est) |
|---|---|---|---|
| Click Calculate | |||
About
A stable concrete slab relies more on its subbase than the concrete itself. Insufficient subgrade thickness or failure to account for material compaction ratios often leads to cracking and settling. This calculator addresses the "shrinkage" factor-the volume lost when loose aggregates like sand or crushed stone are mechanically compacted.
For example, crushed stone typically compresses by 30% (1.3x factor). To achieve a 4 inch compacted base, you must order 5.2 inches of loose material. This tool provides precise ordering volumes for the concrete plate, vapor barrier, gravel base, and optional insulation layers suitable for your climate zone.
Formulas
The volume V is derived from length L, width W, and depth D. The "Order Amount" accounts for the Compaction Factor Cf.
Recommended insulation R-value is determined by the Delta-T of the Climate Zone:
Reference Data
| Material | Compaction Factor | Loose Volume per 1 yd³ Compacted | Typical Use |
|---|---|---|---|
| Concrete (Wet) | 1.03 (Spillage) | 1.03 yd³ | Slabs, Footings |
| Crushed Stone (#57) | 1.20 - 1.30 | 1.30 yd³ | Drainage Layer |
| Sand / Stone Dust | 1.15 | 1.15 yd³ | Leveling |
| Bank Run Gravel | 1.35 | 1.35 yd³ | Structural Fill |
| Topsoil | 1.40 | 1.40 yd³ | Landscaping (Not Subgrade) |