Drill Pattern Spacing Calculator

Work out drill pattern spacing instantly with clear inputs, formula shown and shareable results.

About Drill Pattern Spacing Calculator

Burden is commonly set at 25-35 times the blasthole diameter, and spacing at 1.0-1.3 times the burden for a staggered pattern. Sub-drilling of about 0.3 times the burden below grade prevents toe problems and hard digging. Volume per hole is burden x spacing x bench height.

Formulas

Pattern geometry

Burden = burden ratio x hole diameter; spacing = burden x spacing ratio

Volume

Volume per hole = burden x spacing x bench height; sub-drill = 0.3 x burden

Worked example

With the default values below, Drill Pattern Spacing Calculator returns Burden of 4.560. Change any input above and every figure here is recalculated in your browser.

Inputs used

Blasthole Diameterminimum 0.01 mm: 152 mm
Bench Heightminimum 0.01 m: 10 m
Burden To Diameter Ratiominimum 1: 30
Spacing To Burden Ratioaccepts 0.5–2: 1.15

Results

Burden: 4.560
Spacing: 5.244
Rock Volume Per Hole: 239.126
Sub-Drill Depth: 1.368

Step by step

1Values used
2Pattern geometry
3Volume
4Burden= 4.560
5Spacing= 5.244
6Rock Volume Per Hole= 239.126
7Sub-Drill Depth= 1.368

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Blast design is a safety-critical activity governed by explosives regulation. Patterns must be designed by competent persons with flyrock, vibration and airblast assessment.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Blast design is a safety-critical activity governed by explosives regulation. Patterns must be designed by competent persons with flyrock, vibration and airblast assessment.

Frequently Asked Questions

Why stagger the pattern?

A staggered layout distributes explosive energy more evenly than a square pattern, improving fragmentation for the same powder factor. Spacing-to-burden ratios above 1 suit staggered patterns.

What happens if burden is too large?

The charge cannot break to the free face, giving coarse fragmentation, back-break, excessive ground vibration and a risk of the hole venting through the collar with flyrock.