Blast Hole Quantity Calculator

Calculator Inputs

Example Data Table

Formula Used

1) Effective blast area
A_eff = (L × W) × f_edge

2) Area per hole
A_hole = B × S × f_pattern
Where f_pattern = 1.000 (rectangular/square), or 0.866 (staggered).

3) Hole quantity (area method)
N = round(A_eff / A_hole)
Use “Round up” for conservative planning.

4) Hole depth with inclination
D = (H + J) / cos(θ)

5) Charge length and explosive per hole
L_c = max(0, D − T)
m_hole = ρ × π × (d/2)² × L_c

6) Powder factor estimate
m_total = (A_eff × H) × PF

How to Use This Calculator

1. Enter the blast panel length, width, and bench height.
2. Set burden and spacing (directly, or using a spacing factor).
3. Select your drilling pattern and choose an edge factor for boundaries.
4. Add subdrill, stemming, diameter, and inclination to estimate drilling and charge geometry.
5. Provide powder factor and explosive density for total explosive checks.
6. Click Calculate to see results above the form.
7. Use Download CSV and Download PDF after a calculation.

Technical Article

1) What blast hole quantity represents

Blast hole quantity is the practical count of drilled holes needed to break a defined bench panel. For a rectangular panel, quantity is driven mainly by effective area, burden, spacing, and the chosen pattern. This calculator applies an edge factor (0.50–1.00) to reflect boundaries, ramps, and irregular corners.

2) Pattern geometry and productivity

Rectangular and square layouts use an area factor of 1.000, while a staggered pattern uses 0.866. That reduction means staggered layouts often require more holes for the same panel size, but can improve energy distribution. As a planning reference, burden commonly ranges 2.5–4.0 m and spacing often falls near 1.0–1.5 times burden.

3) Bench volume and powder factor check

Broken volume is calculated as effective area multiplied by bench height. A powder factor (kg/m³) converts this volume into a first-pass explosive estimate. Typical planning values can range from about 0.6 to 1.2 kg/m³, depending on rock strength, desired fragmentation, and downstream handling. Use this estimate to compare against the hole-based charge calculation.

4) Hole depth, subdrill, and inclination

Hole depth includes subdrill to reduce toe problems and improve floor control. If holes are inclined, the drilled length increases by dividing vertical depth by cos(θ). For example, a 10.8 m vertical depth at 15° becomes about 11.2 m of drilled length. Stemming reduces charge length and helps confinement.

5) Using outputs for planning decisions

Use the “holes” result to plan drilling time, consumables, and initiation hardware. Compare the grid rows×columns count against the area-method count to identify unusual geometry. If totals differ widely, revisit edge factor, spacing mode, and panel dimensions. Final designs must be validated with site-specific geotechnical inputs and regulatory requirements.

FAQs

1) What is the difference between burden and spacing?

Burden is the distance from a hole row to the free face. Spacing is the distance between holes in the same row. Together they define the area assigned to each hole and strongly influence hole count.

2) When should I use a staggered pattern?

Staggered patterns can distribute energy more evenly and reduce straight-line weakness planes. They may be preferred for improved fragmentation or when controlling vibration and throw, but they can increase drilling quantity for the same panel.

3) What does edge factor do?

Edge factor reduces the usable area to account for ramps, corners, and stand-off requirements. If the panel is irregular or has exclusion zones, use a lower value so the hole estimate reflects real drillable ground.

4) Why compare powder-factor and hole-based explosive totals?

Powder factor provides a fast volume-based estimate, while hole-based totals depend on diameter, charge length, and density. Comparing both helps catch inconsistent inputs, such as unrealistic stemming, diameter, or spacing selections.

5) How do inclination and subdrill affect drilling quantity?

They usually do not change the number of holes, but they increase drilled meters and can change charge length. More drilled length affects time, consumables, and explosive usage per hole.

6) What rounding mode should I choose?

Rounding up is typically safest for planning because underestimating holes can delay drilling and charging operations. Use “nearest” for budgeting checks, and avoid rounding down unless you have confirmed margins and boundaries.

7) Are these results suitable for final blast design?

No. This is a planning and cross-check tool. Final blast design should be prepared and verified by qualified blasting professionals using site geology, face conditions, initiation timing, vibration limits, and legal requirements.