Expression of ranges of numbers is covered in Number ranges.
Numerals or words?
The style recommended in this manual is to use numerals (digits) to express all quantities – whether small or large – in running text. Using numerals emphasises quantities in the text and makes the text look consistent. This style is commonly used when writing for the web.
2 tests 3 weeks 21 days old
A compound word is created by joining 2 or more words together.
Nevertheless, in some cases, it is better to use the word one than the numeral 1. This is where one is acting as an indefinite article in the sentence:
one place [a place] one idea [an idea] one change in ... [a change in ... ]
Exceptions to the use of numerals rather than words include:
- text with 2 series of numbers – use numerals for one series and words for the other, because this is usually easier to read
Many of the drivers booked for drink-driving had previous convictions: 15 had one conviction, 7 had two, and 4 had three or more.
- where numbers occur consecutively – express one as a word and one as a numeral, because this is usually easier to read, but use numerals for numbers that occur with units of measurement
... from a group of thirty 2-month-old cows.
- any number starting a sentence – write it out, or recast the sentence (especially if it is a large number or a currency)
Seventy samples were collected. or We collected 70 samples.
not
70 samples were collected.
A commonly used alternative style is to use words for quantities under 10, and to use numerals for numbers of 10 or more:
two tests three weeks 21 days old
Exceptions to this style include:
- a series containing some numbers of 10 or more, and some less than 10 – use numerals for all
7 fruits, 9 vegetables and 20 cheeses not seven fruits, nine vegetables and 20 cheeses
- a mix of numbers less than and more than 10 when the numbers are related – use numerals for all
On a property with 900 cattle, 12 died and 6 were sick.
A farmer reported nervous signs in 2 goats from a herd of 200.
- numbers on webpages.
The style to use will depend on the document, how often numerical values occur and the style preference of the organisation the document is being prepared for.
Reminder. Consider using numerals rather than words for all numbers in text.
Regardless of the style chosen, use numerals with units of money or measurement, and for dates, time, periods of time, temperature, mathematical relationships, percentages, ages and quantities:
$5 billion 2 kg 350 km 9 October 2014 1990s 9 am 3 weeks 25 °C 1:50,000 map 2:1 10× eyepiece 5-in-1 vaccine 3% 8 days old 4 times as large 4-fold
If it is necessary to spell out numbers in full, use hyphens in numbers between 20 and 100:
twenty-three fifty-six one hundred and thirty-two
Zero and one
Spell out zero and one if they are used in a general sense:
One of the species was found.
… on one occasion.
His level of understanding was zero.
Use numerals if the zero or one is connected with a unit or specifies a value:
1 mL 1 year a mean of 0 y = 0
or occurs in a series of related numbers:
separated into 1, 3, 5 or 7
1 fruit, 9 vegetables and 20 cheeses
On a property with 900 cattle, 1 died and 6 were sick.
Fractions and ordinal numbers
Write fractions in full in running text, and use a hyphen:
two-thirds three-quarters one-twentieth
For quantities greater than 1, use a built-up fraction, with the numbers closed up:
2⅔
or space the numbers:
2 2/3
Spell out 1-digit ordinal numbers:
first third ninth
Use numerals for ordinals with 2 or more digits. Do not leave a space before th, nd or rd, and do not use superscripts:
If the ordinal numbers are linked in a series, use numerals for all:
The 1st, 2nd and 11th
Reminder. Use a hyphen in fractions written out in words (e.g. two-thirds).
Negative numbers
Indicate a negative number with a minus symbol or an en dash closed up to the number:
–3.5 –3.2 °C
Express a range that includes a negative number with from and to, to remove any confusion with the minus symbol that is used to indicate the negative number (use the same form throughout the document):
Overnight temperatures in June ranged from +2 to –4.2 °C.
Word processing tip
To insert an en dash:
In Windows (e.g. Microsoft Word), use Ctrl+- on the numerical keypad; use Alt+0150 on the numerical keypad; or insert from the symbol set (special characters). On a Mac, use Option+-. Word can also be set up to convert 2 hyphens (--) to an en dash (–) using the autocorrect options.
Large numbers
Write numbers with 4 or more digits with commas:
The convention of using a nonbreaking space (e.g. 12 000) in place of a comma (e.g. 12,000) is trending back towards use of a comma, to improve the ability of screen readers to interpret the number.
In tables, because large numbers can be difficult to read, it is often preferable to scale units or use scientific notation (e.g. 5 × 104 rather than 50,000). Where scientific notation is used, this must be done consistently (see Functional design for tables and Functional design for graphs).
In the text, when writing large numbers ending in several zeros, either substitute a higher order unit or add an appropriate power (superscript) to a basic unit of measurement:
6 million or 6 × 106
not
6000000 or 6 000 000 or 6,000,000
Note: In Australia, as in the United Kingdom, the ‘official’ definition of billion was originally 1 million million (1012). However, it is much more common for 1 billion to mean 1,000 million (109), as is the case in the United States. Australian and international standards (AS ISO 1000-1998: The international system of units [SI] and its application) now acknowledge this as standard usage. However, because of the potential for confusion, use of billion should be avoided; alternatively, it should be defined as 109 or 1012 at the first use.
For the unit parts per billion (ppb), the definition of billion is 109 (see Relative quantities).
Small numbers
Always use a zero before the decimal:
0.25 not .25
Consider using smaller units if there are many decimal places:
23 mg not 0.023 g
For very small numbers, use scientific notation, and use a minus sign, not a hyphen or en dash:
6 × 10−6 not 0.000006
6.0 × 10−6 not 0.0000060 [if the number is precise to 2 significant digits]
Plural numbers
Do not include an apostrophe in plural numbers or years:
100s and 1,000s not 100’s and 1,000’s
the 1960s not the 1960’s
Numbers used as adjectives
When numbers are used adjectivally, use a hyphen when the unit is spelled out in full, but not when the unit is abbreviated:
16-hectare field 16 ha field 3-day wait 50-tonne roller 30 cm column 5-year-old child
See also Compound words.
Significant digits and rounding
The number of digits reported for a quantity should reflect its precision and trustworthiness. For example:
- if a document is reporting the range in leaf length for a species, and many measurements have been taken in tenths of centimetres, give the range in tenths of centimetres
- weights measured with a scale accurate to 0.1 g should be reported in tenths of grams, not hundredths of grams
- percentages based on small sample sizes (<100) should be reported as whole numbers; expressing them to 1 decimal place probably has little scientific value and can be distracting to the reader.
Calculated values (e.g. means) based on raw measurements should be reported to a maximum of 1 significant digit past the accuracy of the original measurement:
Raw measurements for leaf length: 5.4 cm, 3.8 cm, 5.5 cm, 4.9 cm, 5.1 cm
Mean: 4.94 cm
When rounding a number to a certain number of significant digits, leave the digit unchanged if the digit to the right of the last significant digit is below 5, but increase it by 1 if the digit to the right of the last significant digit is equal to or above 5. For a number rounded to 3 significant digits:
9.542 becomes 9.54
9.548 becomes 9.55
9.555 becomes 9.56