Drill Pattern Calculator
Bolt circle mode gives the X/Y coordinates of N equally spaced holes on a pitch circle (start angle, center offset, partial arc, CW or CCW). Blast mode estimates burden, spacing, hole depth, charge and powder factor for a bench blast.
For a bolt circle (pitch circle diameter D) with N equally spaced holes, hole k sits at angle θₖ = start angle + k × 360° ÷ N, with X = center X + (D ÷ 2)·cos θₖ and Y = center Y + (D ÷ 2)·sin θₖ, measured counter-clockwise from the +X axis.
Use the Drill Pattern Calculator
Bolt circle inputs
0° = +X axis (3 o'clock); use 90° to start at 12 o'clock. Arc span 360° = full circle.
Hole coordinates
| Hole | Angle | X | Y |
|---|
Copied.
Bolt circle chord factors
Hole-to-hole distance = PCD × factor, for N equally spaced holes on a full circle. The last column is the distance on a 100 mm (or 100 in) circle.
| Holes | Angle step | Factor sin(180°/N) | On 100 PCD |
|---|---|---|---|
| 3 | 120° | 0.86603 | 86.603 |
| 4 | 90° | 0.70711 | 70.711 |
| 5 | 72° | 0.58779 | 58.779 |
| 6 | 60° | 0.50000 | 50.000 |
| 8 | 45° | 0.38268 | 38.268 |
| 10 | 36° | 0.30902 | 30.902 |
| 12 | 30° | 0.25882 | 25.882 |
| 16 | 22.5° | 0.19509 | 19.509 |
| 20 | 18° | 0.15643 | 15.643 |
| 24 | 15° | 0.13053 | 13.053 |
Pattern Inputs
Common range: 76 – 381 mm
Representative density only; replace with the supplier's loaded bulk density.
Suggested by rock type; editable for site data.
Full Pattern Parameters
Pattern Diagram (plan view)
Blue circles = drill holes. Dashed lines show burden (B) and spacing (S). Gray arrows indicate free face.
Enter your drill and rock parameters, then click Calculate Pattern.
Quick answer
For a bolt circle (pitch circle diameter D) with N equally spaced holes, hole k sits at angle θₖ = start angle + k × 360° ÷ N, with X = center X + (D ÷ 2)·cos θₖ and Y = center Y + (D ÷ 2)·sin θₖ, measured counter-clockwise from the +X axis. Adjacent holes are D × sin(180° ÷ N) apart. For a blast drill pattern, burden is roughly 25–40 × the hole diameter (30 × 152 mm ≈ 4.6 m with ANFO) and spacing is 1.0–1.15 × burden.
Examples
| Pattern | Hole positions (X, Y) | Hole-to-hole distance |
|---|---|---|
| 6 holes on 100 mm PCD, start 0° | (50, 0), (25, 43.301), (−25, 43.301), (−50, 0), (−25, −43.301), (25, −43.301) | 50.000 mm |
| 5 × 114.3 mm wheel pattern, start 90° | (0, 57.150), (−54.353, 17.660), (−33.592, −46.235), (33.592, −46.235), (54.353, 17.660) | 67.184 mm |
| 4 holes on 4.000 in circle, start 45° | (1.414, 1.414), (−1.414, 1.414), (−1.414, −1.414), (1.414, −1.414) | 2.828 in |
| Blast: 152 mm hole, 10 m bench, ANFO, medium rock | Burden 4.56 m × spacing 4.56 m, hole depth 11.37 m | — |
Choose Bolt circle for machining coordinates or Blast pattern for bench blasting, then enter your values.
Summary
A drill pattern is the layout of holes you need to drill. This calculator covers the two common meanings. In machining and fabrication it is a bolt circle: N holes equally spaced on a pitch circle diameter (PCD). Enter the number of holes, the diameter, the start angle and the center position to get the X and Y coordinate of every hole, the angle between holes, the hole-to-hole (chord) distance, a scaled diagram, and the coordinates as CSV or a G81 X/Y list for a CNC or DRO. Partial arcs and clockwise numbering are supported, and common wheel lug patterns such as 5×114.3 load with one click. In surface mining it is a blast pattern: the calculator estimates burden, spacing, subdrill, stemming, hole depth, explosive charge per hole and powder factor from hole diameter, bench height, rock and explosive, as a starting point for a qualified blaster.
How it works
- Bolt circle: enter the number of holes, the pitch circle diameter (or radius), the angle of the first hole and the center X/Y. 0° points along +X (3 o'clock) and angles increase counter-clockwise unless you choose clockwise.
- For a full circle the angle step is 360° ÷ N; for a partial arc it is the arc span ÷ (N − 1), so the first and last holes sit at the ends of the arc.
- Each hole is placed at X = cx + r·cos θ and Y = cy + r·sin θ, rounded to the decimals you choose. The chord between neighbours is 2r·sin(step ÷ 2).
- Blast pattern: burden B = Kb × hole diameter × (RWS ÷ 100)^⅓, spacing = 1.0 × B (square) or 1.15 × B (staggered), subdrill = max(0.3B, 8d) and stemming = max(0.7B, 20d).
- Charge per hole = column volume × explosive density; powder factor = charge ÷ broken volume (kg/m³) or ÷ broken mass (kg/t).
Use cases
- Laying out flange, hub, wheel or motor-mount bolt holes on a mill, drill press or with a DRO.
- Getting X/Y coordinates for a CNC drilling cycle (G81) or CAD from a PCD and hole count.
- Checking a wheel bolt pattern such as 5×114.3 or 6×139.7 and the distance between lug holes.
- Placing holes on a partial arc, for example 5 holes across 120°.
- Designing an initial burden and spacing for an open-pit or quarry bench blast.
- Estimating explosive per hole and powder factor before a site trial.