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Precious metals and stones 

Trade measurement laws regulate the buying, selling and valuating of precious stones or metals when using a measuring instrument, such as a scale.

These laws do not cover other factors you consider when determining price, including:

  • metal purity
  • colour
  • link type
  • workmanship
  • rarity
  • design popularity.

Weighing precious stones

Any scale you use to weigh diamonds or other precious stones must not have a verification scale interval of more than:

  • 10 mg
  • 0.01 metric carats (CM) where the capacity of the instrument is less than 5000 CM
  • 0.05 CM where the capacity of the instrument is at least 5000 CM.

The verification scale interval is the graduation size that a scale will calculate weight by, for example a gram, milligram or metric carat increment.

Weighing precious metals

You can’t use a scale to weigh gold, silver or other precious metals when it has:

  • a verification scale interval that is greater than the interval specified for the scale’s capacity
  • a capacity specified in the first column of the following table, unless it has a verification scale interval equal to or less than that specified in the second column.
Capacity of instrument Verification scale interval
Less than 1 kg 10 mg
1 kg or more but less than 10 kg 100 mg
10 kg or more 1 g

If you use a scale below the minimum capacity marked on the data plate it can be inaccurate.

A verification scale interval is denoted as the ‘e’ value marked on the data plate of a scale. Before purchasing a scale, you should check the ‘e’ value to ensure that it meets these requirements.

Using scales

If you use a scale to weigh precious metals or stones, you must ensure that:

  • the National Measurement Institute (NMI) has approved your type of scale 
  • servicing licensee has verified your scales 
  • you and your staff use the scales in the correct manner (e.g. level and indicating zero before use)
  • you position the scales so that the customer can easily see the weighing process (if not, you must provide a written statement of the weight)
  • you keep the scales clean and in good working order
  • a servicing licensee verifies the scales after each repair or adjustment.

You are responsible for making sure the scale is correct at all times.

We recommend that you check your scales daily to ensure their accuracy. You can purchase a set of test weights from a certifying authority to check that your scales are level, resets to zero and accurate.

We also recommend that you have your scales checked regularly by a technician licensed by NMI (servicing licensee). For a list of servicing licensees, email

Regulating the sale and valuation of precious metals and stones

The National Measurement Act 1960 and the National Trade Measurement Regulations 2009 regulate how precious metals and stones are sold by measurement.

NMI employs trade measurement inspectors throughout Australia. They inspect precious metals and stones being sold or valuated to ensure that sellers are following the correct process.

If an inspector finds that you are short-measuring your customers, you could be fined up to $222,000 per offence.

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