Stockpile Grade Blending Calculator
Work out the tonnage-weighted blended grade when two or three stockpiles are combined into a single feed. Larger stockpiles pull the blended grade toward their own grade, so a simple average of the grades is usually wrong - this tool weights each grade by its tonnage.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the tonnes and grade for stockpile 1 and stockpile 2 (both required).
- Optionally enter the tonnes and grade for a third stockpile - fill both fields or leave both blank.
- Use the same grade unit (all % or all g/t) for every stockpile, then read the blended grade, total tonnes and total contained units.
How it works
The blended grade is the sum of each stockpile's tonnes multiplied by its grade (the contained units), divided by the total tonnes. This is a tonnage-weighted average, so a large low-grade pile outweighs a small high-grade one.
Worked example
Worked example. Blending 1,000 t at grade 2 with 3,000 t at grade 1 gives contained units of (1,000 x 2) + (3,000 x 1) = 5,000 over 4,000 t total, so the blended grade is 5,000 / 4,000 = 1.25 - much closer to 1 than 2 because the second pile is three times larger.
Common mistakes
- Taking a plain average of the grades instead of weighting by tonnage.
- Mixing grade units - do not blend a % grade with a g/t grade.
- Filling only one of the two stockpile-3 fields; enter both or leave both blank.
Frequently asked questions
Can I blend grades in g/t and percent together?
No. The tool is unit-agnostic but assumes every stockpile uses the same unit. Convert them to a common unit first, then blend.
What are 'total contained units'?
It is the sum of tonnes x grade across all stockpiles - the numerator of the weighted average. In percent mode it is tonne-percent; in g/t mode it is effectively grams of metal.
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Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.