How to Calculate Stockpile Volume
Inventory arguments end when the survey is good. Here are the three methods that survive an audit, in ascending order of effort — and the honest accuracy each one buys you.
01Method 1: Geometry — the 5-minute answer
For a conical pile: V = πr²h/3, using base radius and height. A cone 60 ft across and 25 ft tall: π × 30² × 25 ÷ 3 = 23,562 ft³ = 873 CY. Windrows: treat as a triangular prism plus half-cones. Accuracy: ±10–20% on a tidy pile, worse on sprawl. Fine for a daily glance; not for the balance sheet.
02Method 2: GPS walk — the surveyor's baseline
Walk RTK GPS over the pile on a grid plus toe and crest lines, build a surface, subtract the base. Accuracy improves to roughly ±5–8% depending on point density — and it works when weather grounds the drone. The catch: an hour per big pile, and someone climbing loose material with steel toes and a prayer.
03Method 3: Drone photogrammetry — the modern standard
Fly an automated grid at 200–300 ft with 75/75 overlap, ground control or RTK/PPK positioning, process to a surface, subtract the base. A whole yard flies in 20 minutes, every pile at once, at 1–3% accuracy on well-defined piles. This is why quarter-end inventory arguments quietly died at operations that adopted it.
04Get the base surface right — it's half the answer
Volume error hides under the pile. Fly or survey the empty pad once and lock it as the reference base; a pile sitting on old material or a sloping pad against an assumed flat base can swing 10%+ all by itself. Same basemap every survey, forever.
05Convert volume to tons with a defensible density
Tons = CY × loose density ÷ 2000 (if density in lb/ft³, tons = CY × 27 × pcf ÷ 2000). Loose crushed stone commonly runs 90–105 pcf — but 'commonly' isn't a signature. Belt-scale reconciliation or bucket tests on your actual products beat the handbook every time; density error passes straight through to dollars.
06Reconcile and document
Compare survey tons to book tons, explain variances over your threshold (2–5% typical), and file the flight log, control report, and surface files. An inventory number without documentation is an opinion with decimals.
ShotRock flies exactly these surveys under Part 107 with engineering-grade reporting — methodology, accuracy statement, and reconciliation table included.
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Figures are approximate, compiled from public sources as of mid-2026, and rounded for readability. Rankings shift with markets, mergers, and new discoveries. Nothing here is investment, legal, or engineering advice for a specific site — for that, hire an engineer. We know one.