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Rock Young's Modulus Calculator

Estimate intact and rock mass Young's modulus from UCS and RQD using Deere modulus ratios, Rowe & Armitage, and Zhang & Einstein correlations.

Last updated 26 May 2026

About this tool

Estimate Young’s modulus for intact rock and rock mass from UCS and RQD. The tool uses Deere (1968) modulus ratios for intact modulus, Rowe & Armitage (1987) for a direct UCS correlation, and Zhang & Einstein (2004) for RQD-corrected rock mass modulus.

Three rock type categories are available with typical modulus ratio (MR) values: Low ratio (<200, clay-rich rocks), Medium ratio (200–500, sedimentary), and High ratio (>500, crystalline). Based on the Deere & Miller (1966) classification scheme. Enter RQD optionally to get the rock mass modulus estimate.

Essential for preliminary settlement and deformation analysis in rock foundations, tunnels, and slopes.

How to use this tool

1. Enter UCS in MPa — from lab testing or estimated from index tests.

2. Enter RQD (optional) — required for the Zhang & Einstein rock mass modulus.

3. Select rock type — determines the modulus ratio for intact modulus calculation.

Technical information

Ei = MR × UCS — intact modulus. MR classes per Deere & Miller (1966): Low <200, Medium 200–500, High >500.

Em = 215 × √UCS — Rowe & Armitage (1987)

Em = 10^(0.0186 × RQD - 1.91) × Ei — Zhang & Einstein (2004)

Limitations

Modulus ratios vary significantly. The values used are mid-range estimates from Deere (1968). For design, use lab-measured Ei where available.

The Zhang & Einstein method is empirical with considerable scatter. It is best suited for preliminary estimates, not detailed design.

Rock mass modulus depends on discontinuity characteristics not captured by RQD alone. For important projects, consider the Hoek & Diederichs (2006) method using GSI.

Revision history

26 May 2026: Initial release

Disclaimer

This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.

Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.

All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.

By using this tool, you accept full responsibility for how you interpret and apply the information provided.

Spotted an error? Let us know.

UCS (MPa)

RQD (%) — optional

Required for Zhang & Einstein rock mass modulus. Leave blank for intact modulus only.

Rock type (for modulus ratio)

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