Shotcrete Volume Calculator
Shotcrete (sprayed concrete) volume is estimated as a slab: the in-place design volume equals the surface area multiplied by the design thickness, Volume = area × thickness.
Enter Values
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How to use this calculator
- Enter the surface area you need to cover in square metres (measure the actual rock or mesh face, not the plan footprint).
- Enter the design (nominal) lining thickness in millimetres from your ground-support standard.
- Optionally enter a rebound/waste allowance percent — leave blank for the design volume only, or use 10–40% for dry-mix to size the batch quantity.
How it works
Shotcrete (sprayed concrete) volume is estimated as a slab: the in-place design volume equals the surface area multiplied by the design thickness, Volume = area × thickness. Thickness is entered in millimetres and converted to metres (÷ 1000) so the result is in cubic metres. This is the volume of material that actually remains on the wall as the finished lining.
During spraying a portion of the material bounces off the surface and is lost — this is rebound. The calculator scales the in-place volume up by (1 + rebound%/100) to give the sprayed (batch) volume you must supply, and reports the difference as rebound waste. It assumes a uniform thickness over a flat area; irregular profiles, overbreak, laps and pump losses can push real consumption higher, so it is a batching estimate, not a design figure.
Worked example
75 mm shotcrete over a 120 m² backchamber, 20% rebound. For a 120 m² rock surface sprayed to a 75 mm design thickness with a 20% rebound allowance: in-place volume = 120 × 0.075 = 9 m³. Sprayed volume to batch = 9 × (1 + 20/100) = 10.8 m³, of which 1.8 m³ is rebound waste. Order about 10.8 m³ of shotcrete to leave a 9 m³ lining on the wall.
Common mistakes
- Entering thickness in metres instead of millimetres (e.g. 0.075 instead of 75) — the field expects millimetres, so 75 means 75 mm.
- Forgetting the rebound allowance, which under-orders the batch: the in-place volume is the lining that stays, not the amount you have to spray.
- Using the plan (footprint) area instead of the actual sprayed surface area — arched backs and walls have more surface than their plan projection.
Frequently asked questions
What rebound percentage should I use?
Rebound depends on the process, mix and orientation. Dry-mix shotcrete commonly loses 10–40% (higher overhead and on hard, dry rock), while modern wet-mix with accelerator is typically lower, around 5–15%. Use your site's measured figure where you have one; otherwise 20% is a common planning default for dry-mix.
Does this include overbreak or an irregular profile?
No. The calculator assumes a uniform design thickness over the area you enter. Overbreak, uneven rock profiles, mesh gaps and laps increase real consumption. For a design-lining volume only, leave rebound blank; add a suitable allowance to cover profile and rebound when sizing a batch.
Is the result the amount to order or the finished lining?
The emphasised 'sprayed volume to batch' is what you need to supply, including rebound waste. The 'in-place design volume' is the finished lining thickness that remains on the wall. The difference is the rebound/waste volume.
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