Numbers

Numerals vs words

The use of numerals versus words is primarily a matter of convention. The following conventions are recommended:

• Use numerals for 10 and above.

• Spell out zero through nine if the number does not precede a unit of measure or is not used as input that is typed. Unless intended as a measurement, units of time usually follow the spelled-out rule (five years).

• For round numbers of 1 million or more, use a numeral plus the word, even if the prefix number is less than 10.

Correct

10 trucks

ten 50-tonne trucks

five books

two years

1,000

one thousand

zero probability

7 million

7,990,000

Incorrect

2 trucks

0 offset

eighteen books

twelve recommendations

1 thousand

seven million

Adjectival compounds

Only hyphenate a number and its unit of measure when preceded by another number. In such cases, spell out one of the numbers. Do not hyphenate if it contains an SI symbol. Spelled-out compound adjectives containing numbers are, otherwise, usually hyphenated.

Correct

24 one-kilogram weights, a 1-kilogram weight, 1 kg weight

twenty-five 150-tonne trucks, twenty-five 150 t trucks

two-year outlook, 100-year forecast

five-page report, 50-page report

one-quarter-of-an-inch tolerance, ¼ in. tolerance, a tolerance of 0.25 inches

Measurements

Use numerals for all measurements, even if the number is under 10. This is true whether the measurement is spelled out, or replaced by a symbol. Measurements include distance, temperature, volume, size, weight, pressure, energy, voltage, picas, and so on, but generally not units of time unless intended as a measurement.

Correct

0 inches

3 metres, 3 m

3-metre-by-5-metre pad, 3 m x 5 m pad

12 tonnes, 12 t

5 megawatt generator, 5MW generator

0.75 gram, 0.75 g

1% error

90-percent confidence interval, 90% confidence interval

50 percent of the population

two years, 100 years

8 h 56 min 34.2 s

200 Mtpa

Multiple categories

Maintain consistency among categories of information; that is, if one number in a category requires a numeral, use numerals for all numbers in that category regardless of their value. When two numbers that refer to separate categories must appear together, spell out one of them.

Correct

One region has 16 groups, one has 7 groups, and the third has only 5 groups.

fifteen 120-page copies

Numbered sections

Use numerals for coordinates in tables or worksheets and for numbered sections of documents.

Correct

row 3, column 4

Volume 2

Chapter 10

Part IX

step 1

page 74

note 11

no.1 and no.23 [no space after the period]

line nos 1, 5, and 23

Numbers from examples

Do not truncate or round off numbers taken from examples. Show exactly as they appear in the example, but format according to this guide. For example, if the number is formatted “13 877,93”, then reformat as “13,877.93”.

Negative numbers and ranges

Use an en dash, not a hyphen, with negative numbers and ranges. Use a spaced en dash when the limits include symbols or are phrases.

Correct

–73

pages 18–26

28% – 33%

At the beginning of a sentence

Never start a sentence with a numeral. If necessary, add a modifier before a number. If starting a sentence with a number cannot be avoided, spell out the number.

Correct

At this time, 129 clients have registered.

Eleven examples are included.

A total of 27 percent of the population agree.

Incorrect

129 clients have registered.

11 examples are included.

27 percent of the population agree.

Compound numbers

Hyphenate compound numbers when they are spelled out.

Correct

Twenty-five types are included.

the forty-first user

Fractions as words and decimals

Express fractions in words or as decimals whenever possible, whichever is most appropriate for the context. Avoid decimal fractions of time unless meant as a measurement.

Hyphenate spelled-out fractions used as adjectives or nouns. Connect the numerator and denominator with a hyphen unless either already contains a hyphen.

Correct

one-third of the page

three sixty-fourths

two-thirds completed

two-and-a-half weeks (2½ weeks)

3.8 seconds

Aligning decimals

In tables, align decimals on the decimal point. Use an initial zero for decimal fractions less than one.

Correct

0.5 inch

type .5 in

Singular vs plural

When units of measure are not abbreviated, use the singular for quantities of one or less, except for zero, which takes the plural.

Correct

0.5 metre

0 litres

5 kilometres

Incorrect

5 kms

Ordinal numbers

Ordinal numbers designate the place of an item in a sequence: first, second, and so on. Spell out in text, even when more than nine; that is, do not use 1st, 2nd, 12th, and so on. Do not use ordinal numbers for dates unless the reference is relative to the start of any month.

Correct

The intersection is on the eighty-first row.

The meeting is scheduled for 13 April.

Payment must be made on the fifteenth day of each month.

Incorrect

The intersection is on the 81st row.

The meeting is scheduled for 13th April.

Commas and spaces in numbers

In general, use commas in numbers that have four or more digits, regardless of how the numbers appear in the data source. When a series of large numbers are separated with commas or have 10 or more decimal places before the decimal point or 6 or more decimal places after, format the number, before and after the decimal point, with spaces (see Coordinates). When designating years and baud, however, use commas only when the number has five or more digits. Do not use commas in page numbers, addresses, and decimals.

Correct

1,024 bytes

page 1091

1,093 pages

1.06377 m

34 915, 8 400, 202

12 390.729 236 01

54 882 101.35 m E, 2 907 335.04 m N

10,000 BC

9600 baud

14,400 baud

Incorrect

page 1,091

2492 days

4,400 Park Avenue

34,915, 8,400, 202

12,390.729236012

54,882,101.35 m E, 2,907,335.04 m N

2,000 BC

1,200 baud

Ranges of numbers

Use “from” and “through” to describe inclusive ranges of numbers most accurately, except in a range of pages, where an en dash is preferred. Avoid using “between” and “and” to describe an inclusive range of numbers because it can be ambiguous.

Where space is a problem, as in tables and online material, use an en dash to separate ranges of numbers. Use a spaced en dash when the limits include symbols or are phrases and repeat the unit.

You can use hyphens to indicate page ranges in an index if you need to conserve space.

Correct

from 9 through 17

1985–1990

pages 112–120

25 kW – 50 MW

15% – 25%

Incorrect

between 9 and 17

from 1985 – 1990