Grams per Tonne to Ounces per Tonne Converter
Grades of precious metals are quoted either in grams per metric tonne (g/t) or in troy ounces per metric tonne (oz/t, also written opt).
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 your grade in ONE field only — either g/t or oz/t — and leave the other blank.
- Read the converted grade; the tool also shows the equivalent in ppm (1 g/t = 1 ppm by mass).
- Open the steps panel to see the exact multiply/divide by 31.1035 (grams per troy ounce).
How it works
Grades of precious metals are quoted either in grams per metric tonne (g/t) or in troy ounces per metric tonne (oz/t, also written opt). Because one troy ounce is defined as exactly 31.1035 grams, the two are a fixed linear conversion: oz/t = g/t ÷ 31.1035, and g/t = oz/t × 31.1035. This converter fills in whichever field you leave blank.
g/t is also numerically identical to parts per million (ppm) by mass — one gram of metal in one tonne (1,000,000 g) of rock is one part per million — so the tool reports the ppm value too. Note this is TROY ounces per METRIC tonne; do not confuse it with avoirdupois ounces (28.3495 g) or short/long tons, which give different numbers. The converter is pure arithmetic and runs entirely in your browser.
Worked example
Convert a 3.5 g/t gold grade to oz/t. A drill-core assay returns a gold grade of 3.5 g/t. Enter 3.5 in the g/t field and leave oz/t blank. The converter divides by 31.1035 (grams per troy ounce): 3.5 ÷ 31.1035 = 0.1125 oz/t (troy). It also shows the grade as 3.5 ppm, since 1 g/t equals 1 ppm by mass. So 3.5 g/t Au ≈ 0.1125 oz/t.
Common mistakes
- Using the avoirdupois ounce (28.3495 g) instead of the troy ounce (31.1035 g). Precious-metal grades always use troy ounces.
- Mixing tonne bases — this tool uses the metric tonne (1000 kg). A short ton (907.18 kg) or long ton (1016 kg) changes the oz/ton result.
- Filling in both fields at once. Enter only the grade you have and leave the other blank so the converter can compute it.
Frequently asked questions
Why divide by 31.1035?
One troy ounce — the mass unit used for precious metals — equals exactly 31.1035 grams. So a grade in grams per tonne, divided by 31.1035, gives the number of troy ounces in that same tonne, i.e. oz/t.
Is g/t the same as ppm?
By mass, yes. One gram of metal in one metric tonne (1,000,000 grams) of rock is one part per million, so 1 g/t = 1 ppm. The converter shows the ppm value alongside the oz/t result.
Does this use troy or avoirdupois ounces?
Troy ounces (31.1035 g), the standard for gold, silver and platinum-group metals. It is not the avoirdupois ounce (28.3495 g) used for everyday weights.
What tonne does oz/t refer to?
The metric tonne (1000 kg). If your data uses short or long tons, the ounces-per-ton figure will differ and this tool should not be used directly.
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