Blast Pattern Designer
Designs a surface bench drill-and-blast pattern — hole depth, charge column, charge per hole, powder factor and whole-pattern totals (explosive, tonnes, drilling) — with a plan-view hole grid, a hole section and design-ratio checks.
Bench & hole geometry
Explosive, rock & layout
Metric bench blasting. Burden is the distance to the free face (or the previous row); spacing is the distance between holes along a row. Everything runs in your browser.
Charge & powder factor
Pattern totals — 32 holes (4 × 8)
Pattern plan
Hole section
Powder factor = charge per hole ÷ (burden × spacing × bench height). Charge per hole = charge length × linear charge, where linear charge = (π/4)·(Ø/1000)²·(density×1000). A planning and study aid only — blasting is safety-critical; a licensed shotfirer must sign off the design against site conditions and regulations.
Before you rely on this: Safety-critical: treat this as a preliminary check only. Always verify against the governing standards and have a competent person review the result before use.
How to use this calculator
- Enter the bench height, hole diameter, burden, spacing, subdrill and stemming.
- Pick the explosive (or type its density), set the rock density and the number of rows and holes per row, and choose a square or staggered pattern.
- Read the powder factor, charge per hole and pattern totals, and check the design-ratio warnings before you drill.
How it works
The hole depth is the bench height plus subdrill, and the charge column is the hole depth minus the stemming. The linear charge concentration is (π/4)·(Ø/1000)²·(density×1000) kilograms per metre, so the charge per hole is the charge length times that concentration.
Each hole breaks a block of burden × spacing × bench height. The powder factor — the key blasting number — is the charge per hole divided by that volume, in kilograms of explosive per cubic metre of rock. Multiplying by the number of holes gives the total explosive, volume, tonnes and metres drilled.
The tool also checks the usual design ratios — burden as a multiple of hole diameter (typically 25–40×), spacing-to-burden (about 1.0–1.5), and enough stemming and subdrill — and flags anything outside the normal range so obvious flyrock or toe problems are caught early.
Worked example
Worked example. A 10 m bench, 89 mm holes on a 2.5 × 3.0 m staggered pattern with 0.5 m subdrill and 2.0 m stemming, charged with ANFO (0.85 g/cc): hole depth 10.5 m, charge length 8.5 m, ~5.29 kg/m, ~45 kg per hole. Each hole breaks 75 m³, so the powder factor is about 0.60 kg/m³. A 4 × 8 pattern (32 holes) uses ~1,438 kg of explosive to break ~2,400 m³ (~6,240 t).
Common mistakes
- Entering the hole diameter in metres instead of millimetres — the charge concentration is very sensitive to diameter (it squares).
- Forgetting subdrill, which leaves a high floor / toe, or over-stemming, which chokes the charge and coarsens the top of the muckpile.
- Treating the output as a final design — powder factor and pattern must be verified against the rock mass, the explosive supplier's data and a licensed shotfirer.
Frequently asked questions
What is a good powder factor?
It depends on the rock and the result you want, but surface bench blasting is often around 0.3–0.8 kg/m³ — softer rock and easier digging at the low end, hard, massive rock and fine fragmentation at the high end. This tool reports the powder factor from your geometry and charge so you can compare it to your site norm.
How are burden and spacing chosen?
Burden is commonly 25–40 times the hole diameter for bench blasting, and spacing is usually 1.0–1.5 times the burden (staggered patterns often use about 1.15× for an equilateral layout). The tool shows these ratios and warns when they fall outside the usual range.
Is this suitable for a real blast design?
No — it is a planning and study aid. Blasting is safety-critical; a licensed shotfirer or blast engineer must design and sign off the real pattern against the site geology, the explosives supplier's data, vibration and flyrock limits and the relevant regulations.
Related tools
- Powder Factor Calculator (kg per BCM)
- Blast Pattern Area Calculator
- Blast Timing Delay Calculator
- Blast Vibration Safe Distance Calculator
- Blast Hole Count Checker
- Blast Volume Calculator
Explore more in Mining, Quarry, Earthworks, Drill & Blast.
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.