Blast Drill Pattern Calculator

Summary

Enter hole diameter, rock density, and explosive properties to get burden, spacing, subdrill, and stemming for an optimal blast pattern.

How it works

1. Enter the blast hole diameter (mm) and select the rock type to set typical density and hardness values.
2. Adjust the explosive relative weight strength (RWS) for your specific product or use the ANFO default.
3. The calculator derives the burden (B) using the empirically validated ratio B = Kb × d, where Kb ≈ 25–40 depending on rock conditions.
4. Spacing is set at 1.0–1.15 × burden for square/staggered patterns; subdrill is typically 0.3 × burden.
5. Stemming is calculated as 0.7 × burden; total hole depth = bench height + subdrill.
6. Review the output table and adjust the Kb multiplier slider if field conditions require tighter or wider patterns.

Use cases

• Designing initial drill patterns for a new open-pit bench.
• Verifying that a contractor-supplied pattern matches rock conditions.
• Scaling patterns when switching to a larger or smaller drill rig.
• Estimating explosive quantity per hole and per blast block.
• Training junior blasting engineers on pattern geometry fundamentals.
• Comparing square versus staggered grid layouts for the same bench.

Frequently Asked Questions