Treatment of numbers and measures

General usage
Specific usage
International System of Units (SI)

General usage

Depending on the context and subject area, it may be appropriate to express numbers and units of measurements either as words or numerals. A list of the names and symbols of some common units of measurement is given below.

In the absence of specific instructions, the following advice applies when using numbers and measures in general written work. For information on usage in technical work, please consult your recommended textbooks or take advice from your lecturers.

Numbers

In works where numbers occur frequently, use words for all numbers under 10 .
In works where numbers occur rarely, use words for all numbers under 100.
Use words for all numbers that begin a sentence, even in technical text.
Use words for ordinal numbers (first, second, third, etc.) up to 100.
Use numerals with symbols and in mathematical expressions, tables, graphs, etc.
Use numerals when referring to figures, tables, pages, years, and so on.

Units of measurement

Unit names should be used in general text of non-technical or non-scientific work.
Unit symbols may be used in general text of technical or scientific work.
Unit symbols should be used in all mathematical expressions, tables and graphs.
Unit symbols should be teamed with numerals, not words (e.g., 8 m, not eight m).
Unit names may be teamed with numerals or words (e.g., 245 kg; 245 kilograms) depending on how the number is presented (see 'Numbers', above).

Specific usage

The following table shows number and measure usage in specific cases. Note that these are general examples. Students presenting work in technical or scientific subject areas should follow the usage prescribed or recommended by their lecturer or School.

ITEM	TREATMENT	EXAMPLE
Unit names	Write unit names in lower case. Pluralise as appropriate.	one metre; four metres; 231 kilograms; metres per second
Unit symbols	Separate unit symbols from numerals by a space. Use a slash for division of symbols. Write symbols in lower case, except if derived from personal names. Do not pluralise.	1 m; 4 m; 231 kg; m/s
Mathematical operators	Separate numerals and operators by a space.	2 + 7 = 9
Pos/neg value	No space is required after the plus or minus sign.	+99; -20
Ratios	No space is required before or after the colon.	1:33
Percentages	Express percentages in numerals. Depending on context, the word 'percent' may be used with a numeral in general text. No space between numeral and symbol.	87%; 87 percent
Large numerals	Numbers of five or more digits should be separated into groups of three digits by a space or a comma depending on usage in your subject area.	269 234; 12 856; 4 786 899 269,234; 12,856; 4,786,899
Millions, billions	The use of million (thousand x thousand or 10⁶) is permitted by the Australian Standard. In almost all situations, billion can be taken to mean thousand x million (or 10⁹). In scientific work, use exponential notation.
Currency	No space is used between symbol and numeral. When expressing currency in millions, use one of three treatments, depending on context.	A$200; US$45; €40; ¥211 $3 700 000; $3.7 million; $3.7m
Ordinal numbers	In general text of works where numbers are used rarely, use words for ordinal numbers up to 100. In works where numbers are used frequently, use the numeral form.	Word: 'first', 'second', 'third', etc. Numeral: '1st', '2nd', '3rd', etc.
Eras	Separate year and era by a space.	65 BC; 1006 AD
Decades	No space or apostrophe between decade and 's'.	1980s
Dates	Use numerals for days and years, and words for months.	2 May 1985
Times of day	Separate time and time of day by a space.	6.30 am; 9.00 pm

International System of Units (SI)

In Australia, all measurements are based on the International System of Units (SI), although some old English units remain in general use. Always use SI units, except if quoting from a source using other units, or if other units are more appropriate (usually for historical reasons), or if instructed otherwise. The final authority is Australian Standard AS1000-1979: International System of Units (SI) and its Application.

COMMONLY USED SI UNITS
Quantity	Unit Name	Symbol
length	metre	m
mass	kilogram	kg
electric current	ampere	A
time	second	s
thermodynamic temperature	kelvin	K
luminous intensity	candela	cd
amount of substance	mole	mol
plane angle	radian	rad
frequency	hertz	Hz
force	newton	N
pressure, stress	pascal	Pa
energy, work	joule	J
power	watt	W
potential difference	volt	V

The following is a selection of the most commonly used multiples. Prefixes are prescribed for factors from 10¹⁸to 10^-18. The prefix name or symbol is combined with the unit name or symbol to form a single word or single symbol (e.g., word: kilo + gram = kilogram; symbol: k + g = kg).

MULTIPLES OF SI UNITS
Factor	Prefix	Symbol	Examples
10³	kilo	k	km; kPa
10⁶	mega	M	MW
10⁹	giga	G	GHz
10^-2	centi	c	cm
10^-3	milli	m	mg; mV
10^-6	micro	µ	µA
10^-9	nano	n	ns; nm

The following non-SI units are accepted by the Australian Standard as permissible due to their widespread use and practical importance.

NON-SI UNITS
Measure	Unit name	Symbol	Note
Area	hectare	ha	1 ha = 10 000 m²
Volume, capacity	litre	L or l	Use L where 'l' may be confused with '1'
Mass	tonne	t	1 t = 1000 kg
Time	day, hour, minute	d, h, min