Site investigation · Laboratory: compaction & field density
California Bearing Ratio (lab) calculator
Load–penetration curve to CBR at 2.5 and 5.0 mm, with swell and pavement subgrade notes.
Standard: AS 1289.6.1.1 · 13.2 kN @ 2.5 mm, 19.8 kN @ 5.0 mm
Open the live calculator → All site investigation calculators
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Penetration (mm), load (kN) | 0, 0 0.5, 0.25 1.0, 0.55 1.5, 0.85 2.0, 1.12 2.5, 1.36 3.0, 1.55 4.0, 1.88 5.0, 2.15 7.5, 2.70 10, 3.10 | |
| Swell after soaking | 0.8 | % |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Load at 2.5 mm | 1.36 | kN |
| Load at 5.0 mm | 2.15 | kN |
| CBR at 2.5 mm | 10.3 | % |
| CBR at 5.0 mm | 10.9 | % |
| Reported CBR | 10.9 (5.0 mm) | % |
| Swell | 0.8 | % |
- ✓ Curve starts without concave-up seating (else correct origin)
- ✓ Swell ≤ 2 % (typical subgrade limit; check spec)
Method, formulas and assumptions
- CBR = load at penetration / standard load × 100
- Standard loads 13.2 kN at 2.5 mm and 19.8 kN at 5.0 mm
- Report the higher value; if a concave-up start exists, shift the origin first (not automated here)
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.