# Measurement and units

Standard units of measurement support readability and accuracy. Express precise values for users by combining numerals with the correct unit symbol.

## Use the standard units of measurement

Australia uses the metric system for most quantities:

The National Measurement Institute oversees Australian units of measurement. The governing legislation is the National Measurement Act 1960.

Don’t use the non-SI legal units of measurement for international content. The exception is when you have checked that users will understand and accept them.

Rules for units of measurement:

• Punctuation: don’t place a full stop after a unit of measurement.
• Capitalisation: use capitals only if the unit represents a proper name.
• Plural and possessive: units don’t have a plural or possessive form.
• Start of a sentence: write out the unit in full.
• Spacing: use a non-breaking space between the number and the unit.

### Example

• ‘m’ for metre
• ‘kg’ for kilogram
• ‘W’ for watt

### Accessibility requirements

Measurements and units can include:

• symbols (for example, ‘μ’ for ‘micro’
• superscript (a number, letter or symbol placed above a line – for example, the ‘2’ in ‘$km2$’).

Unless they are coded correctly, symbols and superscript may be inaccessible for some people who:

• have low vision
• use screen readers to access content.

Insert symbols and superscript with tools such as:

These make mathematical equations and symbols accessible, including for screen readers.

Ensure both symbols and superscript can be enlarged without loss of content or functionality. Don't use images of symbols or superscript.

Resources:

WCAG quick reference: 1.3.1 Info and relationships – level A

## Write numerals with units of measurement

Use numerals, not words, for numbers when you are referring to a unit of measurement:

• Always use numerals next to a unit of measurement.
• Include a non-breaking space between the number and the unit.

• 5 t
• 5 tonnes

• five t
• five tonnes

## Use symbols for common units of measurement

You don’t need to spell out units of measurement, even for the first use, if they’re well known and users will know what they mean.

### Example

• ‘mm’ for millimetres
• ‘cm’ for centimetres
• ‘km’ for kilometres
• ‘km/h’ for kilometres per hour

Spell out units of measurement the first time you use them if users won’t immediately understand them. After that, use the symbols.

### Example

The noise from the building site was 120 decibels (dB). Workers in the nearby office preferred a limit of only 50 dB.

Don’t combine symbols and words for units.

### Like this

Queensland is 1,853 million $km2$ in area.

### Not this

Queensland is 1,853 million square km in area.

### SI prefixes for large and small quantities

Internationally accepted prefixes and their symbols make it easier for users to read, understand and compare numbers. Use them in government content.

Table 1 details common prefixes and their symbols.

A complete list of prefixes and symbols is available at The International Bureau of Weights and Measures (BIPM).

Table 1: Commonly used prefixes for SI units
Prefix Symbol Factor Extended form
tera T $1012$ 1,000,000,000,000
giga G $109$ 1,000,000,000
mega M $106$ 1,000,000
kilo k $103$ 1,000
hecto h $102$ 100
deca (also ‘deka’) da $101$ 10
deci d $10−1$ 0.1
centi c $10−2$ 0.01
milli m $10−3$ 0.001
micro µ $10−6$ 0.000001
nano n $10−9$ 0.000000001

Note: the International Bureau of Weights and Measures uses ‘deca’ but this is spelled ‘deka’ in Schedule 3 of the National Measurement Regulations.

#### Example

• 63 megalitres is 63,000,000 litres
• 0.001 metre is 1 millimetre

Don’t use non-standard units.

#### Like this

• There was 5 μg of active ingredient in each capsule.
• He measured 50 mL of water.

#### Not this

• There was 5 mcg of active ingredient in each capsule.
• He measured 5 dL of water.

### Data storage and transfer

The prefixes for data storage and transfer work differently to those used for SI units. ‘Byte’ (B) is the unit of storage and data transfer speed. For this purpose, use:

• ‘kilobyte’ for 1,024 B
• ‘megabyte’ for 1,024 kB
• ‘gigabyte’ for 1,024 MB
• ‘terabyte’ for 1,024 GB.

### Units of time

Days, years, hours and minutes measure time. These are not SI units. Spell them out in full – unless they’re in a table, list or chart and are easy to understand.

#### Example

• I have been working in the public service for 12 years.
• He started in the new department 20 days ago.
• They sent the report in the last 15 minutes.

Use symbols for units that are derived from time measurements, such as speed.

#### Example

The speed limit for urban areas in NSW is 50 km/h.

## Put a non-breaking space between numbers and units

People will read the number and its unit as a measurement only if the two components sit together. To do this, use a non-breaking space between numbers and their units of measurement.

Without a non-breaking space, a unit could reflow to the next line. This would separate it from the quantity, making it difficult for users to understand the information being presented.

Although this is important for all content, it’s more likely to happen on smaller screens, such as those on mobile devices.

### Like this

The post should be at least 1.5 m tall.

[The sentence has a &nbsp; inserted between ‘1.5’ and ‘m’.]

### Not this

The post should be at least 1.5
m tall.

[A bad line break between the measurement and its unit]

By convention, some industries don’t have a space between the quantity and the unit. Many 750 mL bottles of wine, for example, have the volume 750ml printed on the label.

Check the preferred style if you are writing for a specialist application.

## Don’t add ‘s’ for plural forms

Symbols for units of measurement represent both the singular and the plural forms. Don’t use an ‘s’ to show plural with the symbols for units.

56 km

56 kms

## Compare measurements using the same units

Make it easy for users to compare quantities. Use the same:

• unit and prefix
• number of decimal places.

### Like this

• The Green Wattle Creek fire burnt almost 3,000 $km2$, of which more than 1,000 $km2$ was national park.
• The smaller jug held 1.5 L and the bigger jug held 2.0 L.
• The piece of wood was 140 mm by 1,320 mm by 20 mm.

### Not this

• The Green Wattle Creek fire burnt almost 300,000 ha, of which more than 1,000 $km2$ was national park.
• The smaller jug held 1,500 mL and the bigger jug held 2 L.
• The piece of wood was 14 cm by 1.32 m by 20 mm.

## Only use non-SI units if the user understands them

There are other units that are also Australian legal units of measurement but are not SI units. They’re listed in Schedules 1 and 2 of the National Measurement Regulations.

These non-SI units are not all legally accepted in every country. Use them only if users will understand them. Some units, such as the nautical mile, are for use only in Australia. Table 2 details common examples of other legal Australian units.

Table 2: Examples of other commonly used legal units in Australia
Quality Name Symbol
sound intensity decibel dB
area hectare ha
length nautical mile n mile
mass tonne t
time day d
time hour h
time minute min
velocity knot kn
volume litre L or l
blood pressure millimetre of mercury mm Hg
work and energy kilocalorie kcal

Note: ‘litre’ can be represented as ‘L’ or ‘l’, depending on the type of content and who will be using it. Most government content should use ‘L’ as it’s clearer to users (‘l’ can be confused with ‘I’ and ‘1’).

## Avoid imperial units

Don’t use imperial units of measurement in Australia unless you have a specific reason, such as:

• in quotations from historical documents
• when writing for readers in countries (particularly the United States) where imperial measures, or elements of them, still apply.

### Example

• gallons for volume of fuel
• barrels for volume of oil
• inches for the size of a screen
• feet for the altitude of a plane

It’s good practice to also provide the equivalent quantity in SI units when that helps users.

### Example

In the 1970s, the speed limit for highways in many states of Australia was set at 60 miles per hour (97 km/h).

## Release notes

The digital edition consolidates information from the sixth edition about measurement and units. It links to external sources for more detailed information.

The digital edition follows advice from the sixth edition about including a space between the number and unit of measurement.

This is contrary to the recommendation in the Content Guide, which recommended omitting the space between number and measure.

### Evidence

BIPM (International Bureau of Weights and Measures) (n.d.) SI brochure: the international system of units (SI), BIPM website, accessed 4 June 2020.

Oxford University Press (2016) ‘14.1.4: units’, New Oxford style manual, Oxford University Press, Oxford.

University of Chicago (2017) ‘9.16: numbers with abbreviations and symbols’, Chicago manual of style, 17th edn, University of Chicago Press, Chicago.

### References

American Psychological Association (2020) Publication manual of the American Psychological Association, 7th edn, American Psychological Association, Washington DC.

BIPM (n.d.) The international system of units (SI), International Bureau of Weights and Measures website, accessed 4 June 2020.

Harder DW and Devitt S (2003) ‘Units in MathML’, W3C working group note, W3C website, accessed 3 June 2020.

The Unicode Consortium (2020) Unicode 13.0 character code charts, Unicode website, accessed 2 June 2020.