Rock Bolt Quantity Calculator

Plan bolting layouts quickly with flexible, reliable spacing inputs. Compare square or triangular grids instantly. Download CSV and PDF summaries for your team onsite.

Tip: Submit once to enable CSV and PDF downloads.
Used in exports and reports.
Choose how you want to enter coverage area.
Triangular increases density for the same spacings.
Coverage length along the surface.
Coverage width of the surface.
Center-to-center spacing along length.
Center-to-center spacing across width.
For irregular surfaces, setbacks, or rework zones.
Extra bolts near ribs, corners, and interfaces.
Design conservatism for rock class uncertainty.
Allow for breakage, misdrills, and spares.

Example data table

Scenario Area input Pattern sx (m) sy (m) Allowances Estimated bolts
Tunnel crown 40 m × 6 m Square 1.5 1.5 Perimeter 8%, Safety 1.10, Waste 5% ~144
Slope face 300 m² Triangular 2.0 2.0 Overlap 5%, Perimeter 10%, Waste 7% Varies by inputs
Shaft lining 25 m × 4 m Square 1.2 1.2 Perimeter 5%, Safety 1.05, Waste 5% Varies by inputs

Formula used

1) Base area
If using Length × Width:
BaseArea = Length × Width
If using Direct area:
BaseArea = Area
2) Area per bolt (coverage cell)
Square: CellArea = sx × sy
Triangular: CellArea = sx × sy × (√3 / 2)
Triangular assumes staggered rows with similar spacings.
3) Adjusted effective area
EffectiveArea = BaseArea × (1 + Overlap% / 100)
4) Raw bolts (before allowances)
RawBolts = EffectiveArea / CellArea
5) Final bolts (with factors)
Final = ceil( RawBolts × (1 + Perimeter%/100) × SafetyFactor × (1 + Waste%/100) )
ceil() rounds up to whole bolts.

How to use this calculator

  1. Select your area input method: Length × Width or Direct area.
  2. Choose the bolt pattern that matches your design layout.
  3. Enter sx and sy spacings using center-to-center distances.
  4. Add overlap and perimeter allowances for irregular geometry.
  5. Set a safety factor based on rock mass uncertainty.
  6. Include waste for spares, breakage, and field changes.
  7. Press Calculate to view results above the form.
  8. Use Download buttons to export CSV or PDF reports.
Good practice: Validate the bolt pattern and spacing against drawings, rock class, and support specifications before procurement.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.