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Blast Fragmentation Calculator

Predict blast fragmentation using the Kuz-Ram model. Calculate X50 mean fragment size, X80, X20, and powder factor from blast design parameters.

Last updated 21 July 2026

About this tool

Predict blast fragmentation using the Kuz-Ram model (Cunningham 1983, 1987). Enter burden, spacing, bench height, charge weight, rock factor, and explosive strength to get mean fragment size (X50), plus X20 and X80 from the Rosin-Rammler distribution.

Also calculates powder factor (kg/m³) — the key parameter linking explosive consumption to blasted volume. Useful for blast design optimisation, fragmentation prediction, and crusher feed assessment.

How to use this tool

1. Enter blast geometry — burden, spacing, and bench height in metres.

2. Enter charge and explosive details — charge per hole (kg) and explosive RWS (ANFO = 100).

3. Set the rock factor — 7-9 for soft, 9-11 for medium, 11-13 for hard rock.

Technical information

X50 = A × (V/Q)^0.8 × Q^(1/6) × (115/RWS)^(19/30)

Rosin-Rammler distribution with uniformity index n = 1.0 (typical quarry blast). After Cunningham (1983, 1987).

Limitations

The Kuz-Ram model is empirical and gives approximate predictions. Actual fragmentation depends on geological structure, timing, confinement, and water conditions not captured by the model.

Uniformity index is fixed at 1.0. For more accurate predictions, the full Cunningham uniformity equation should be used with detailed blast geometry.

Revision history

21 July 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.

Burden (m)

Spacing (m)

Bench height (m)

Charge per hole (kg)

Rock factor A

Soft: 7-9, Medium: 9-11, Hard: 11-13

Explosive RWS (ANFO = 100)

ANFO: 100, Emulsion: 90-120

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