Measurement adjustment

Measurement adjustment is a nationally-agreed process designed to improve heavy vehicle compliance with mass and dimension limits. The national objective is to ensure enforcement action is based on the highest degree of accuracy achievable at any time.

What is measurement adjustment?

The measurement adjustment applies to heavy vehicles when being weighed or measured for on-road complaince and enforcement purposes.

Measurement adjustment recognises that a mass or dimension assessment outcome may potentially vary from time to time, due to the:

  • weighing and measuring equipment used
  • inspection site characteristics
  • measuring methods
  • conditions under which the measurements are made.

By applying an agreed adjustment to account for these possible variations, the measurement is based on the highest degree of accuracy achievable at any time. This means the assessment can legally be relied upon in considering possible enforcement action.
For example, when an axle is loaded exactly at the legal limit, it is possible that the measured mass (as indicated on weighing equipment) could be slightly higher or slightly lower than the legal limit, due to the variations in the mass assessment process being used.

The measurement adjustment ensures that allowances are made for these factors before a decision is made on whether an offence has actually occurred. Enforcement officers determine the weighing site category and apply the appropriate measurement adjustment to calculate the assessed mass.

Who does it affect?

Measurement adjustment impacts drivers, operators, loaders, packers, consignors or any other responsible person who influences the mass or dimension of the vehicle or its load.

How do I comply?

Operators should take all reasonable steps to ensure vehicles are loaded within their legal mass and dimension limits. Under the chain of responsibility, all parties in the supply chain must ensure their acts or omissions do not cause or contribute to a breach of vehicle mass or dimension legal limits. Operators should also encourage other parties in their supply chain to be aware of their legal obligations and comply with them at all times.

Mass measurement adjustment

How is mass measurement adjustment (MMA) applied?

MMA relies on two key concepts:

  • measured mass (MM)—the  reading obtained from the weighing equipment
  • assessed mass (AM)—the  measured mass minus the relevant MMA.

MM – MMA = AM

The assessed mass is calculated by subtracting the measurement adjustment from the vehicle’s mass as shown on the measuring equipment.  The assessed mass is compared with the mass limit and breakpoints to determine the severity of any offence that may have occurred.

What are the mass weighing site categories?

Enforcement officers determine the weighing site category and apply the appropriate measurement adjustment to calculate the assessed mass. There are 3 categories of mass weighing sites:

  • Category 1—a weighbridge or weighing platform and portable scales on a concrete surface.
  • Category 2—a site that does not fall under Category 1 and that has a bitumen surface.
  • Category 3—a site that does not fall under Category 1 or Category 2.
Mass measurement adjustments 
Axle group

Site category 1

Site category 2

Site category 3

Single (single tyres) 0.3 0.3 0.4
Twin steer or tandem axle (single tyres or combination of single and dual tyres) 0.3 0.4 0.5
Single (dual tyres) 0.4 0.4 0.5
Tandem (dual tyres) 0.5 0.5 1.0
Tri-axle or Quad-axle 0.5 0.5 1.0
Gross mass 0.25t 0.5t 1.0t

Note: The measurement adjustment is applied for each weighing step when determining gross vehicle mass. That is, the measurement adjustment is applied for each movement of the vehicle onto the scales that is needed to weigh all of the axles. Therefore, multiple measurement adjustments may be applied for some gross mass calculations.

How does it work?

The relevant MMA for each axle (or axle group) mass and gross mass is calculated based on the:

  • number of axles in the axle group, including the number of tyres
  • site category
  • number of vehicle movements required to weigh the vehicle.

Example: If a Category 1 weighing site with a single weighing plate weighed a typical 6-axle prime mover semitrailer combination, its gross weight would be calculated in two steps.

  • The prime mover would be moved onto the platform and weighed and then the trailer axle group would be moved onto the platform and weighed.
  • This equates to two adjustments of 250 kg each, making the measurement adjustment for the gross weight of the example vehicle 500 kg. Enforcement action may be taken when a vehicle’s assessed mass exceeds the legal limit.

Dimension measurement adjustment

How is dimension measurement adjustment (DMA) applied?

DMA relies on two key concepts:

  • measured dimension (MD)—the reading obtained from the measuring device.
  • assessed dimension (AD)—the measured dimension (MD) minus the relevant DMA.

MD – DMA = AD

DMA is deducted from the measured dimension (MD) to determine the assessed dimension (AD). 

The assessed dimension is compared with the dimension limit and breakpoints to determine the severity of any offence that may have occurred.

Dimension measurement adjustment (DMA)
Dimension measured Adjustment category Amount in millimetres Application of DMA
Height Category 1 30mm

All height measurements where:

  • the site is an even surface
  • the highest point can be identified by line of sight
  • the highest point is accessible with a height stick.
Category 2 100mm All height measurements that do not meet Category 1
Width Category 1 20mm All width measurements
Length Category 1 100mm Vehicles that are not eligible to operate over 26 metres in length
Category 2 300mm Vehicles that are eligible to operate over 26 metres in length