Whether or not to spell out numbers or express in numerals depends partly on the length of the piece. In longer prose, spell out numbers one to nine; use numerals for 10 upwards, unless the number starts the sentence, in which case it should be spelled out. Do not mix the two styles within a paragraph when they refer to the same category:
Twenty students were present at the lecture
There were 20 students present
At least 8 of the 20 students were not concentrating
Eight of the twenty students were not concentrating
In general, 8 or 10 students were present at all three lectures
In the last example listed, numerals are used for one category, and the number is spelled out for the other category: this is acceptable.
Shorten number extents, including in dates:
24–5, 106–7; 245–54; 1980–91; 2006–7
(NOTE the en rule)
NOTE that numbers in the group 10 to 19 are not shortened:
16–19; 112–14; 310–11
NOTE that in titles and headings, dates are generally not shortened:
The Life of Charles Dickens, 1837–1896
Spans in bc years are not shortened (NOTE the small caps rule):
190–155 bc
(190–55 bc is a century longer)
When specifying a range use either ‘from xxx to xxx’, or ‘xxx–xxx’
The period from 1910 to 1940
The period between 1910 and 1940
BUT: The period 1910–40
DO NOT USE: The period from 1910–40
NOTE that the financial year uses a solidus, not an en rule:
The financial year 2007/8
The academic year 2007–8
Use figures for measurements attached to units:
5kg; 10oz
Use figures for ages:
The 5-year-old boy
PERCENTAGES: use ‘per cent’ in longer prose, % in tables and figures and in shorter pieces or where space is tight. Whichever is used, be consistent and adopt the same system throughout the text.
Always use numerals, not words, for percentages and fractions:
50%; 50 per cent; 2.5%; 2.5 per cent
MONEY
In longer prose, ‘£50 million’, ‘£1 billion’ should be spelled out. In shorter pieces and captions, or where there is more than one column on the page, these can be expressed as ‘£50m’ and ‘£1bn’.
TIME:
9am, 10.30am, 6–7pm
(NOTE the en rule). Or use the 24-hour clock:
19.00. 13.50.
SPACING
Insert a single space in the following instances:
p. 5, pp. 16–25, 250 bc, ad 950
Do not insert a space in the following:
9am, 3.30pm, 3lb, 7kg, 25cm. $4m, 25%
(BUT 25 per cent)