In this section: Overview of number formatting  Examples of number formatting  Exceptions for numbers and ordered events less than 10  Numbers with five or more digits  Ranges of numbers  Number hyphenation  Large numbers
Overview of number formatting
 Numbers and ordered events less than 10 in full should be written as words, not numerals (see examples), although there are some exceptions.
 Numbers with two or more digits should be written as numerals unless they are at the start of a sentence (see examples).
 Numbers between 1000 and 9999 should contain no punctuation.
 Numbers with five or more digits should include commas (not decimal points or full stops).
 Use ‘from’ and ‘to’ instead of a dash to describe a range of numbers in text. Numbers written out in full should be hyphenated appropriately.
 Often, judgement is needed to determine the best presentation for a set of numbers.
Examples of number formatting
Correct 
Incorrect 
We sent the review to four referees. 
We sent the review to 4 referees. 
The 10 participants agreed. 
The ten participants agreed. 
The 25 studies are available. 
The twentyfive studies are available. 
Thirtythree adults and five children participated. 
33 adults and 5 children participated. 
Ninth 
9th 
112th 
one hundred and twelfth 
Exceptions to basic rule for numbers and ordered events less than 10
Exception 
Guidance 
Example 
Sentence contains numbers < 10 and ≥ 10 
Acceptable to use only numerals 
from 2 to 12 years from 5% to 25% of the number of participants There were between 9 and 15 people in the room. 
Equations, numerical results, statistics 
Numerals only 
2/20 OR 1.06 (95% CI 0.90 to 3.02; 6 trials, 1500 participants) (3.1% at 6 months versus 4.7% at 5 months) 
Sentence starts with a number 
Spell number 
Eleven per cent of people … Twenty authors attended the workshop. Eight separate doses are described. 
Number with a unit 
Always use numerals 
8 mg 25 mL 6 s 0.7 kg 
Tables (see also: Tables in Cochrane Reviews) 
Numerals for all numbers including those < 10 
— 
Description of a measurement scale  Acceptable to include numeral 
Outcomes were evaluated using the 9point ORBIT classification. 
Numbers with five or more digits
Note: this is an exception to the style convention for SI units; see Units and systems of measurement.
Correct 
Incorrect 
7677 10,000 12,100 
7,677 10000 12.100 
Ranges of numbers
Correct 
Incorrect 
from three to nine participants −12 to −4 The risk ratio was 0.38 (95% CI 0.30 to 0.49) (MD −11.50 h, 95% CI −20.04 to −2.18) 1% to 10% 4 mg to 5 mg 
from three  nine participants −12  −4 The risk ratio was 0.38 (95% CI 0.300.49) (MD −11.50 h, 95% CI −20.04  −2.18) 1%10% 45 mg, or 4 to 5 mg 
Number hyphenation
Rule 
Correct 
Incorrect 
Hyphenate compound numbers from twentyone through to ninetynine 
ninetyseven one hundred and fortytwo

ninety seven onehundredandfortytwo forty three thousand and eightythree 
Hyphenate writtenout fractions 
twothirds twofifths 
two thirds two fifths 
Large numbers
Use '6.1 million' rather than '6,100,000'
Avoid 'billion' and 'trillion', due to ambiguity about their value. If they are used, they should be explained in terms of millions (e.g. '6 billion (6000 million)')