Mineral Reserve Grade Calculator
This calculator computes the tonnage-weighted average grade of a mineral resource from multiple ore blocks or drill composites. This is the standard method required by JORC Code (Australia/Asia-Pacific) and NI 43-101 (Canada) for mineral resource reporting. Enter pairs of tonnage and grade values, separated by commas, one pair per line or separated by semicolons.
Weighted average grade formula
Grade(avg) = sum(t(i) x g(i)) / sum(t(i))
Where t(i) is the tonnage of block i, g(i) is the grade of block i, and the summation is over all ore blocks above the cut-off grade. This formula is used in all JORC Code and NI 43-101 compliant resource estimates.
Mineral reserve grade calculator: frequently asked questions
What is weighted average grade?
Weighted average grade is the average ore grade of a combined set of ore blocks, each weighted by its tonnage. It is calculated as the sum of (tonnage x grade) for all blocks divided by the total tonnage. This is the standard method for reporting mineral resource grades in JORC and NI 43-101 compliant estimates.
Why must grade be weighted by tonnage?
A simple arithmetic average of grades ignores the fact that different blocks contain different amounts of ore. A small high-grade block should have less influence on the overall grade than a large low-grade block. Tonnage-weighting correctly accounts for the varying contribution of each block to the total resource.
What is a composite in drilling?
A composite is a combination of multiple drill hole intervals, each weighted by their length and grade, to produce a representative sample for resource estimation. The weighted average calculation is the same as for ore blocks: sum of (length x grade) divided by total length.
Can this calculator handle multiple grade elements?
This calculator handles one metal or element at a time. For polymetallic deposits, run a separate calculation for each metal. The weighted average formula is identical for all elements: sum(tonnage x grade) / sum(tonnage).
How is this related to the cut-off grade?
The weighted average grade should be reported above and below the cut-off grade. Only ore above the cut-off grade is counted in mineral resources and reserves. If you apply a cut-off, exclude blocks below that grade from the calculation.
Official sources
- JORC Code 2012: Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves.
- Canadian Securities Administrators NI 43-101: National Instrument 43-101 Standards of Disclosure for Mineral Projects.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.