5. Numbers
This section covers numbers, particularly the question of when they should be written out and what to do should they appear in combination with units of measurement, other numbers and punctuation marks. Although approaches to these issues differ depending on the type of document, these guidelines are intended for institutional rather than technical texts. They also give precedence to British usage, although explanations on American usage are given when necessary. For details on using numbers with currencies, see Section 4.8 Currencies.
5.1 Writing out numbers
5.1.1 Cardinal numbers
Spell out cardinal numbers from zero to nine and use numerals from 10 upwards, but maintain consistency in the immediate context.
Every three sessions, the students will be organised in new groups of five.
The Board will be reviewing a total of 10 new master’s degrees and 12 new doctoral degrees.
The presentations should last between five and ten minutes.
Note that apart from its use in calculations, dates, lists, etc., the concept of zero is usually expressed with the word no, instead of the numeral 0.
There were no students in the classroom.
5.1.2 Ordinal numbers
Spell out ordinal numbers from zero to nine and use numerals from 10 upwards, but maintain consistency in the immediate context. Avoid superscript type.
The Second International Conference on Fluid Dynamics was held in Vic.
The oldest European university was founded in the 12th century.
In this year’s ranking table, the research groups Pattern Analysis and Sonar Imaging occupied third and eleventh position, respectively.
5.1.3 Roman numerals
Use Roman numerals for course names.
Mathematics II
5.1.4 Fractions
Spell out simple fractions and hyphenate them when used as adjectives.
A two-thirds majority vote is required to approve the proposal.
However, avoid hyphens when the fraction is used as a noun.
Two thirds of the students were in agreement.
The lecturer has covered three quarters of the course so far.
5.1.5 Numbers at the beginning of a sentence
Spell out numbers (including years) at the beginning of a sentence, although it is better to rewrite the sentence so that it does not start with a numeral.
Nineteen forty-five was the year the UN was founded.
The UN was founded in 1945.
5.1.6 Plural numbers
Add an s to form the plural of a numeral. Do not add an apostrophe.
Among the scores were four 94s and two 99s.
5.2 Numbers and punctuation
5.2.1 Decimal points
Use a point, not a comma, before a decimal.
0.25
5.5
5.2.2 Commas
In numbers of one thousand or more, use commas between groups of three digits.
2,436
32,548
83,200,000
Do not use commas in serial numbers such as page numbers, street numbers and years.
This idea receives further comment on page 1056 of the report.
All further enquiries should be made at our office at 1558 Brunswick Avenue, New York City.
The University of Bologna is the world’s oldest university; it was founded in 1088.
5.2.3 Hyphens
Hyphenate compound numbers from twenty-one to ninety-nine.
Three hundred and forty-six students are enrolled in the School of Fine Art.
Spell out numbers that are joined to a word by a hyphen, except in the case of set phrases such as 24-hour clock.
A five-year period
A one-week holiday
When two numbers appear side by side, spell one of them out. If one of them occurs alongside a unit of measurement, make that one a numeral.
four 6-week periods
thirty-six 20-cent coins
5.3 Numbers and units of measurement
Spell out the number if the unit of measurement is written out and use a numeral when the unit of measurement is abbreviated.
The surface area of the School’s premises is five hundred square metres.
The conference hall is 2 km from here.
Do not use points or plurals with abbreviated units of measurement. Insert a non-breaking space between the numeral and the unit.
2 m
6 km
10 min
5.4 Numbers and ranges
Use numerals for ranges.
5.4.1 Full numbers
In ranges, always write numbers in full to avoid ambiguity.
*pages 123–5
pages 123–125
*between 18 and 20,000 people
between 18,000 and 20,000 people
5.4.2 Dashes
Use a closed-up dash to indicate a range.
groups of 5–10 students
5.4.3 Symbols
In ranges, repeat those symbols and units that are joined to a numeral.
100°C–150°C
between 100°C and 150°C
20–30 cm
from 20 to 30 cm
For advice on spacing, see Section 4.7 Spacing.
5.5 Time of day
Use numerals for times of day, but spell out the number with the expression o’clock, which is used to designate exact hours only.
If you use the 12-hour clock, write a.m. and p.m. with points and a space between the time and the abbreviation. Use a point to separate hours from minutes.
The lecture starts at 9.30 a.m.
The rector’s speech will begin at four o’clock.
Use noon (or 12 noon) and midnight, rather than 12 p.m. and 12 a.m.
The tutorial, which was due to begin at noon, began at 1.15 p.m.
The campus copy shop closes at 12 noon.
The faculty bar will serve coffee until midnight.
When using a.m. or p.m., avoid a leading zero.
*08.30 a.m.
The rector’s speech will begin at four o’clock.
If you use the 24-hour clock, use a point to separate hours from minutes. Do not use the symbol h.
The meeting is at 18.00.
5.6 Dates
Do not use the endings st, nd, rd or th with a figure in a date. Note that, in British English, dates are written in the order day–month–year, without internal punctuation.
12 July 2020
In British English, the numeric form of the date above is, therefore:
12/07/20
Note that, in American English, dates are written in the order month–day–year, with a comma between the day and the year.
July 12, 2020
In American English, the numeric form of the date above is, therefore:
07/12/20
5.6.1 Days of the week
Do not use a comma after the day of the week when it precedes a date.
Tuesday 6 July 2010
5.6.2 Years
In running text, use all four digits when referring to a year.
’71
1971
5.6.3 Academic years
Write academic years in one of the following two ways, but be consistent. Use a hyphen and not a dash.
the 2023-2024 academic year
the academic year 2023-2024
5.6.4 Decades
Use numbers to refer to decades rather than writing them out. Do not add an apostrophe before the plural s.
They were all born in the mid-1920s.
To refer to the decade from 2000 to 2020, use a circumlocution such as the first decade of the 21st century.
5.6.5 Centuries
Do not use Roman numerals for centuries. Instead, either spell out the century or use the ordinal number.
the XX century
the twentieth century
the XIX century
the 19th century
5.6.6 Festivals and historical events
If a date refers to a festival or historical event, spell out the number.
the Fourth of July celebrations
the Hundred Years’ War
the First of May demonstration
5.6.7 Laws
In citing pieces of legislation, arrange the dates as shown in the examples below.
Spanish Personal Data Protection Law 15/1999, of 13 December
Organic Law 4/2007, of 12 April, amended by Organic Law 6/2001, of 21 December, on Universities
5.7 Use of billion
The term billion is now used to indicate 1,000,000,000 or 109 in most, if not all, English-speaking contexts, following standard American usage. So, a billion is “a thousand million” rather than “a million million”.
5.8 Telephone numbers
Telephone numbers are typically composed of an international call prefix, a country calling code and the local telephone number. To aid legibility, they are split into groups, using spaces and not dashes or points. In the Catalan-speaking territories, the numbers after the country calling code tend to be grouped in threes.
00 34 934 016 186
Note that the international call prefix (00) used to dial out of a country is generally replaced with a plus sign. This is joined to the country calling code, which is used to dial into a country.
+34 934 016 186
Telephone extensions are written at the end of the number, after a space, in brackets.
+34 934 016 186 (182)