5. Grammar
5.1 Writing Numbers
Since numbers represent a central part in any technical or scientific text, they must be written clearly and consistently. As with words, there are rules how to present numbers. Some of these rules are fixed, others vary. You need to check whether the journal you are writing for has particular guidelines that you should follow.
Is it better to present a number in word form or as a numeral?
This is a question writers often face, and the following guidelines and examples should help:
- Do not start a sentence with a numeral. If the number is a long one, then it is best to restructure the sentence so that it does not come at the start.
| wrong | correct |
| 2 specimens of the same powder were used. | Two specimens of the same powder were used. |
| 37 samples of an aluminium-silicon-carbide composite material were compared in the test. | In the test 37 samples of an aluminium-silicon-carbide composite material were compared. |
- Cardinal numbers from zero (0) to ten (10) should be written as words. For numbers above ten, numerals are preferred.
...two particles, three types of pore radii - BUT 12 specimens, 37 samples
This procedure involves four steps: ...
The x and y axes intersect at zero.
We consider two stages in the kinetic crack evolution...
There are some exceptions to this general rule:
- Numbers that are followed by units of measurement or are part of a calculation or mathematical operation remain as numerals. Similarly, figures should be used for numbers associated with age, time, dates, percentages, money, page numbers and proportion, as well as with diagrams, graphs and tables.
340 MHz, 4.5 mg, 3 kg, 4 x 6,
3 years old, 5.30, 5 April, 6 percent, 500 dollars, page 8, 2 to 1
Note: the word percent is normally written out when part of the text. The symbol (%) is used only in headlines, tables and graphs.
- When you have several different numbers in one sentence use figures rather than words. However, when all the numbers are less than 9, it is better to write them as words:
In this laboratory there are 14 measuring instruments, 13 osciloscopes and 11 spectral analysers.
The research centre has five laboratories, three computer rooms and two lecture rooms.
- Ordinal numbers from first to ninth must be written out:
...third stage, first experiment, fifth step
BUT - 20th century, 40th anniversary
Punctuation to use with numbers
- It is customary in Britain and America to use a comma to show thousands and millions, and a full stop (or period) for decimals:
5,300 (= 5 thousand 3 hundred), 1,230,000 (= 1 million 230 thousand),
0.5 (= nought point 5), 0.08% (= nought point nought 8 percent)
- Place a hyphen between a number and the unit of measurement when it is used as an adjectival phrase before a noun (see also Section 5.7 Punctuation). Hyphens are also used with numbers from 21 to 99 and for fractions when written out as words:
a 10-step procedure, a five-year period, a three-layer coating, a 3-cm stripe,
twenty-nine, seventy-eight, two-thirds, one-quarter
- Normally leave a space between the numeral and the quantity or unit of measurement:
37 kJ, 22 mm, EXCEPTIONS: 15%, 4o, 10oC
- Capital letters. Where there is a noun before a numeral it needs to be capitalised. However, if the noun comes after the numeral, e.g. with an ordinal number, it is not capitalised:
Figure 8, Section 5, Table 2, BUT: the seventh figure
- Plurals. With plurals of numbers add the letter s without an apostrophe. However, the apostrophe can be used with plurals of single digit numbers, and in recent years it has become more common to add the apostrophe in other numbers too. (See also Section 5.7 Punctuation)
in the '90s, in the 1980s, BUT: The binary code consists of 1's and 0's.
- Use of the dash. Do not use dashes in a careless way which can cause ambiguity, for example with negative numbers:
| wrong | correct |
| a stripe with the length of 3-4 cm | a stripe with the length of 3 cm - 4 cm |
| with temperatures of -5-30oC | with temperatures of -5 to 30oC |
| from 1990-1995 | from 1990 to 1995 |
| between 20-30 | between 20 and 30 |
