When you buy a kilo of sugar or a litre of petrol, how do you know you are getting exactly the amount you paid for? The National Measurement Institute is on to it.

"Measurement affects everything we do in our lifetime," Gavin Watt, site manager of the institute's Perth headquarters told 720 ABC Perth.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 23 seconds 23 s Weighing a single grain of sugar ( 720 ABC Perth: Hilary Smale )

The Commonwealth agency has 70 inspectors around Australia and a large lab of weights and scales that can check everything from weighbridges where farmers deliver their harvests, down to a single grain of sugar.

Balancing the scales

The inspectors conduct spot checks on businesses and check that their scales are accurate so both traders and customers know they are not being short-changed.

"As a trader, you want to make sure that you are doing the right thing by your customers," Mr Watt said.

"But obviously you are there as a business to make money, so you want to make sure you have your profit margins right as well.

"We try to make sure that traders and consumers know that we are there to assist and to make sure the measurement is accurate."

Back at base, there are a wide range of measurement tools.

And everything must be checked — from hospital light metres used on jaundiced babies, to scales measuring tonnes of iron ore, to ounces of gold.

Weighing equipment at the National Measurement Institute in Perth. ( 720 ABC Perth: Hilary Smale )

"I think we are looking at a grain haul for this season of around 15-17 million tonnes for Western Australia alone," Mr Watt said.

"Every farmer, when they bring their grain into a facility, is being paid on both weight and quality.

"Both the business that is buying the grain and the farmer want to make sure that they are getting accuracy."

Formerly the Weights and Measures Office

The institute was formally created in 2010 but has existed in various forms and names since federation.

"Many people know us still as Weights and Measures," Mr Watt said.

A historical set of scales at the NMI lab, which started as the Weights and Measures Office. ( 720 ABC Perth: Hilary Smale )

"It was annexed to the police department in the early 1900s and then over time it moved to consumer protection in Western Australia.

"From July 1, 2010 all of the trade measurement facilities nationally moved into a single business unit in the Commonwealth Government."

The Perth branch worked in a basement in the city for decades, but last month moved to a new facility in the northern Perth suburb of Malaga.

In 2014-2015, 40 per cent of first-time visits to businesses revealed a breach of trade measurement law.

The institute also runs a hotline that both traders and customers can call if they suspect a measurement is not quite right, or visit the institute's website.