Express a number range using an unspaced en dash or with words (usually from and to, or between and and):
the dose lasted 2–5 days the dose lasted from 2 to 5 days
attended the conference on 3–5 May attended the conference from 3 to 5 May
in the next 10–20 years in the next 10 to 20 years
the reviewer spent 5–10 hours the reviewer spent between 5 and 10 hours
When using an en dash to show a range of numbers with unit symbols, the symbol is needed only after the second number:
20–25 km 3–5 m2 1–5 °C 20–30%
Caution! Do not use from or between when expressing a range with an en dash.
If using words to express a range of numbers with unit symbols, the symbol is needed only after the second number (although it can be used after both numbers):
20 to 25 km or 20 km to 25 km
3 to 5 m2 or 3 m2 to 5 m2
1 to 5 °C or 1 °C to 5 °C
except if the symbol is closed up to the number:
20% to 30% not 20 to 30%
If a range starts a sentence, write out the first number and express the second using a numeral, or (preferably) rewrite the sentence:
Nine to 15 L was extracted. or We extracted 9–15 L.
Ten per cent to 15 per cent of the 300 people tested ... or Of the 300 people tested, 10–15% …
Be careful when using words such as increase by (or from), decrease by (or from) and change by (or from) before 2 numbers in a sentence:
Diameter increased from 2 to 5 cm. [Is this an increase of 2–5 cm or of 3 cm?]
Diameter increased by 2 cm to 5 cm. [Is this an increase of 2–5 cm or of 2 cm?]
The sentence may need to be clarified:
Diameter increased 2–5 cm.
or
Diameter increased by a range of 2 to 5 cm.
or
Diameter increased from an initial value of 2 cm to a final value of 5 cm.