OECD Style Guide (Fourth Edition)

9. Numbers and units of measure

Abstract

Correctly and consistently expressing numbers and units ensures the accuracy and reliability of OECD work. Be aware of differences between English and French common practices for numbers and units.

General rules

• Depending on the context, ordinal numbers can be written in words (one, two, three…), Arabic numerals (1, 2, 3…), or Roman numerals (I, II, III…).

• There are small but significant differences in how numbers are expressed in English and French, explained in the table at the end of this chapter.

See also: Abbreviations, acronyms and signs; Dates and time; Hyphenation; Punctuation.

Cardinal numbers

• Cardinal numbers express quantity and are used for counting.

Do

✔ Express one to ten in words, not figures, except for:

• numbers used with an ISO currency code (USD 6)

• percentages (5%)

• numbers associated with measurement units (3 km, 80 tonnes, 1 L)

• when numbers less than ten and greater than ten occur together in context, write them all in figures

  At the meeting, 12 Member countries and 3 non-Member economies raised the issue.

• numbers followed by “million”, “billion” or “trillion” (1 million, 3 billion, 5 trillion)

• representing scale (on a scale of 0‑10).

✔ Express numbers 11 and above in figures, not words.

✔ When two numbers refer to one item, spell out one of them and express the other in figures, following the rules above.

They requested four 1-metre stands.

✔ Always write a number out in words if it is the first word in of a sentence.

Twelve OECD Member countries raised the same issue.

✔ Always write a number out in words in titles or subtitles.

The report Learning beyond Fifteen: Ten Years of PISA was released in 2012.

✔ For web content, write numbers as digits, not words, with the thousands place separated by a hard space.

✔ For web content, write numbers as digits, not words.

✔ Round off large numbers, particularly in text.

🙁 1 198 650 000

🙂 1.2 billion

See also: Breaks and hard spaces.

Don’t

✘ Use Roman numerals (I, II, III…), unless as part of an individual’s title, the title of a work, or the title of an event or time period.

🙁 Mobile phones became widely used at the end of the XXth century.

🙂 Mobile phones became widely used at the end of the 20th century.

🙁 King Richard the 3rd of England died in 1485.

🙂 King Richard III of England died in 1485.

Decimal fractions

• Numbers containing decimal fractions should always be written in numbers.

• Decimal fractions are always plural.

Do

✔ Express decimal fractions in numerals.

✔ Use a decimal point, never a comma or other mark.

The average family has 2.4 children.

✔ Use a zero, never a blank space.

0.45 (not .45)

✔ Round currency up or down to a full number or give the number to two decimal places.

AUS 1 (instead of AUS 0.92); USD 0.02 (for two cents) EUR 0.20 (for 20 cents).

Non-decimal fractions

Do

✔ Express non-decimal fractions in words.

✔ Hyphenate the numbers in a fraction regardless of whether it is being used as an adjective or noun.

✔ In general, use only readily recognisable fractions such as one-third, one-quarter, one-half.

Three-quarters of the legislators voted for the resolution.

The Senate approved the bill by a two-thirds majority.

Don’t

✘ Use numerals to express non-decimal fractions.

🙁 Over ¼ of the class was absent.

🙂 Over one-fourth of the class was absent.

✘ Use less recognisable forms of fractions.

🙁 The survey showed two-eighths of the territory was uninhabitable.

🙂 The survey showed that 25% of the territory was uninhabitable.

Negative numbers

• Negative numbers always have a value that is less than zero. This is indicated with a minus sign proceeding the numeral (‑446.2).

Do

✔ Use a non-breaking hyphen or the minus key for the minus sign, to ensure the sign and number stay on the same line.

Don’t

✘ Leave a space between the minus sign and the number.

✘ If referring to currencies, put the ISO code first, then the negative number (CAD ‑225).

See also: Breaks and hard spaces; Hyphenation.

Ordinal numbers

• Ordinal numbers express position in an order or series.

Do

✔ Use ordinal numbers sparingly. Overuse is distracting for the reader, particularly in lists.

Don’t

✘ Use the adverbial form of ordinal numbers (firstly, secondly…). Reword the sentence.

🙁 The proposed legislation will help local businesses in two ways. Firstly, it will attract investment to the area. Secondly, it will fund training programmes.

🙂 The proposed legislation will help local businesses by attracting investment and funding training programmes.

Percentages

Do

✔ Use “%” in all text and graphics, except in publication titles, chapter titles, section headings, and when the percentage is the first word of the sentence.

✔ Use “%” or “per cent” in a text when referring to a defined amount.

✔ Use “per cent” (not “%” or “percent”) when the percentage expressed is the first word of the sentence.

Ninety per cent of the participants agreed with the chair’s proposal, but 10% did not.

✔ Use “percentage” when referring to a general proportion or share.

A small percentage of the students needed extra tutoring.

✔ Spell out “percentage points” on first usage followed by (p.p.) and use “p.p.” thereafter.

The survival rate of supported firms was approximately 2.5 p.p. higher than the one of non-supported firms after 12 months.

✔ In general, for a percentage that is a decimal fraction, round to one decimal point. If one or more percentages are a decimal fraction, express any whole number percentages in the same sentence or list with the whole number followed by “.0”.

The inflation rate was 2.2% in November 2024, up from 2.0% in October.

✔ Repeat the % sign after each number in a series.

Last week, 45%, 55% and 65% of the trains, planes and buses ran on time, respectively.

✔ Repeat the “%” sign when per cent ranges are separated by prepositions but not when the range is hyphenated.

On average, 10% to 20% of food is wasted every day.

On average, 10‑20% of food is wasted every day.

Don’t

✘ Use the “%” symbol with a number written as a word; use the numeral instead.

✘ Put a space between the number and the percentage sign.

🙁 The hurricane damaged fifty % of the buildings.

🙂 The hurricane damaged 50% of the buildings.

✘ Use the % sign with non-decimal fractions.

🙁 The price was cut by ¼%.

🙂 The price was cut by 0.25%.

See also: Breaks and hard spaces.

Numbers with four or more digits

• For clarity and simplicity, the OECD has adopted the rule that, for all texts in all languages, numbers containing four or more digits are broken by spaces, not punctuation marks.

See also: Punctuation.

Do

✔ Always use a hard space to separate numbers of four or more digits; never use punctuation nor run numbers together (4 000, 1 275 103, 8 619 673 021).

Don’t

✘ Break numbers across lines. Use hard spaces to indicate the thousands space. No space is needed if referring to a year, page number, legislation, an address or for online content (2025, p. 1001).

Units of measure

• Although most countries and economies use the International System of Units (SI), some continue to use local systems. Use units of measure most appropriate for the topic being discussed.

Do

✔ Separate a number from a unit of measure with a hard space.

✔ Always capitalise units of measure that are derived from a proper name (A [Ampère], Pa [Pascal], kWh [Watt]).

See also: Breaks and hard spaces.

Don’t

✘ Italicise or put in bold units of measure.

✘ Invent symbols or abbreviations for units of measure. See the table below.

Abbreviations for units of measure

 

Length
mm	millimetre
cm	centimetre
m	metre
km	kilometre
in	inch
ft	foot
yd	yard
mi	mile
Surface
m2	square metre
km2	square kilometre	The SI suggests the use of “km2” rather than “hectare” (ha).
ft2	square foot
sq yd	square yard
Weight
µg	microgramme
dg	decigramme
g	gramme
kg	kilogramme
oz	ounce
lb	pound
t	tonne
Mt	million tonnes, megatonnes	Use “Mt” to indicate million tonnes or megatonnes when it is used frequently in the text; otherwise, it should be spelled out. Remember to spell out “Mt” on first use.
Volume (metrics units, SI – litre-based) The SI recommends using an uppercase “L” to avoid confusion with the number “1”.
daL	decalitre
hL	hectolitre
L	litre
Volume (imperial/US customary units)
pt	pint
qt	quart
gal	gallon
Temperature
°C	degree Celsius	Note that Fahrenheit is not used in OECD publications.
Time
s	second
min	minute
hr	hour
y	year
Large numbers
thsd	thousand	Also k (kilo)
mln	million	Also M (mega)
bln	billion	Also G (giga)
tln	trillion	Also T (tera)
Other
A, kA	ampere, kiloampere
Bq	becquerel	Unit of radioactivity
J, kJ	joule, kilojoule
mph	miles per hour
km/h	kilometres per hour
kW/h	kilowatt hour
pkm	passenger-kilometre	Unit measuring how much passenger transport a system provides
px	pixel
tkm	tonne(s)-kilometre(s)	Unit measuring the volume and distance of freight transport
t eq. CO2	tonne of CO₂ equivalent	Unit measuring the climate warming effect of 1 tonne of carbon dioxide
vkm	1 vehicle travelling 1 kilometre	Unit measuring the total distance travelled by vehicles
V	volt	Note that “volt” is lowercase when spelt in full
W	watt	Note that “watt” is lowercase when spelt in full

Key differences between English and French

 

English	French
Four digits and above
For coherency across the official languages, the OECD chooses to use spaces rather than punctuation marks for numbers containing four or more digits (2 618, 32 518, 7 519 000).
Fractions
one-third, two-thirds, three-quarters, etc.	un tiers, deux tiers, trois quarts, etc.
Large numbers
International System of Units (SI) scale, short form:	International System of Units (SI) scale, long form:
million = one million (106)
billion = thousand million (109)	billion = mille milliards (1012)
trillion = thousand billion (1012)	trillion = milliard de milliards (1018)
Ordinal numeral adjectives
1st	1er, 1re
2nd	2e, 2d/2de
3rd	3e
4th, etc.	4e, etc.
Percentages
5%	5#%
Plural numbers
All numbers except 1 generally take the plural:	Only numbers 2 or higher take the plural:
0.7 children per family, 1 child per family, 1.5 children per family	0.7 enfant par famille, 1.5 enfant par famille, 2 enfants par famille
-0.5 degrees, -1 degree, -2 degrees	-0.5 degré, -1 degré, -2 degrés
Second number in groups of ten
twenty-one	vingt et un
thirty-one	trente et un
forty-one	quarante et un
fifty-one	cinquante et un
sixty-one	soixante et un
seventy-one	soixante et onze