Calculator
Grade times width
A rough way of comparing drill intercepts that trades off grade against thickness, and what true width does to it.
The formula
Grade x width = grade multiplied by the intercept length, in gram-metres or per cent-metres. Where a true width is given, the same calculation uses it instead.
What it assumes
- Grade is uniform across the interval, which it never quite is.
- The figure is a comparison aid between similar deposits, not a measure of value.
Where it stops being reliable
- A thick low-grade intercept and a thin high-grade one can give the same number and be worth entirely different amounts.
- Without a true width, the reported interval overstates thickness by an amount that depends on the angle of the hole.
- It ignores depth, continuity, metallurgy and everything else that decides whether rock can be mined.