Troy ounces to grams: conversion for metal prices

Troy ounces to grams: convert metal weights and prices per gram, distinguish ordinary ounces and keep units and rounding explicit.

GuideBy Narwhal API4 min read
A compact green balance weighing a gold bar against a grey calibration weight.

Use the right ounce

An ordinary avoirdupois ounce is exactly 28.349523125 grams. It is not interchangeable with a troy ounce. Spell out the unit in your input and output rather than displaying an ambiguous “oz”.

NIST’s measurement tables distinguish the two systems. The exact gram factor follows from 480 grains per troy ounce and the international pound definition of 7,000 grains and 453.59237 grams.

Convert weights in both directions

For a 10-troy-ounce quantity, multiply 10 by 31.1034768 to obtain 311.034768 grams. For 100 grams, divide 100 by 31.1034768 to obtain approximately 3.21507465686 troy ounces.

A kilogram contains 1,000 grams, so one kilogram is approximately 32.1507465686 troy ounces. These are unit conversions, independent of the metal’s price.

Weight formulas
grams = troy_ounces × 31.1034768
troy_ounces = grams ÷ 31.1034768
kilograms = grams ÷ 1000

Convert the price denominator separately

Use an illustrative quote of USD 2,000 per troy ounce. Dividing by 31.1034768 gives approximately USD 64.3014931373 per gram. Multiplying that unrounded per-gram value by 10 gives approximately USD 643.014931373 for 10 grams. These figures are examples, not a current gold quote.

The unit cancellation explains the direction: (USD / troy ounce) × (troy ounce / 31.1034768 grams) = USD / gram. Multiplying the price by the factor would instead make the smaller unit incorrectly more expensive.

Price formulas: currency unchanged
price_per_gram = price_per_troy_ounce ÷ 31.1034768
price_per_troy_ounce = price_per_gram × 31.1034768
value = grams × price_per_gram

Keep purity and commercial terms separate

A weight conversion does not establish the fine-metal content of an alloy, a dealer’s buy or sell price, or the premium on a finished product. If a calculation uses fine-metal mass, state the fineness assumption separately and confirm what the source quote measures.

Likewise, converting USD per troy ounce into USD per gram does not convert USD into another currency. A separate currency calculation needs an identified exchange rate and date.

Round at the end of the calculation

Retain the full unit factor and enough intermediate precision for the calculation. Round the final displayed amount according to its purpose. Rounding the per-gram quote first and then multiplying by a large weight can create an avoidable difference.

The linked Commodity unit converter displays up to 12 significant digits. Its exact unit definitions do not make the entered weight or a quoted market price more accurate. For accounting calculations, use a documented decimal and rounding policy.

Use the converter for quantities

Open the Commodity unit converter to switch between troy ounces, grams, kilograms, pounds and tonnes. It also estimates containers from an explicitly entered usable payload.

The calculator converts quantities; it does not fetch prices or apply purity adjustments. Use the worked price formulas above only with a quote whose currency, unit, timestamp and product scope you have checked.

Sources and references

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