Calculate blast powder factor (kg of explosive per cubic metre of rock) from the drill pattern.
Powder factor = explosive per hole ÷ (burden × spacing × bench height). At 60 kg per hole on a 3 × 3.5 m pattern, 10 m bench, the powder factor is 0.571 kg/m³.
Calculator
Powder factor
How it works
The rock volume broken by one hole is its share of the pattern: burden × spacing × bench height. Dividing the charge mass by that volume gives the energy applied per cubic metre — the powder factor used to judge fragmentation and cost.
Uses the design pattern and charge for a representative hole and ignores subdrill and stemming volume. Typical surface powder factors fall around 0.3–0.8 kg/m³ depending on rock strength and the fragmentation target.
Frequently asked questions
What is a typical powder factor?
Surface blasting in moderately hard rock is often around 0.3–0.8 kg/m³. Harder rock or finer fragmentation needs a higher factor; soft, blocky ground needs less.
Should I include subdrill in the volume?
This calculator uses bench height only, which is the common convention for design powder factor. If you want the in-situ figure including subdrill, add the subdrill length to the bench height.
Higher powder factor — better fragmentation?
Generally finer fragmentation, but with diminishing returns and more flyrock, vibration and cost. Tune to the downstream needs (digability, crusher feed) rather than maximising it.