Numbers

When applied to countable objects, spell out numbers below 10:

• There are four large detectors at the LHC.
• The LHC construction project had three phases.

For 10 and above, use digits. Numbers up to 9999 do not take a comma or a space. Numbers with five digits take a non-breaking space every three digits. So it’s:

One, nine, 10, 100, 1001 and 9999, but 10 000 or 564 381 or 1 057 983.

Try to avoid putting numbers at the start of a sentence, but if it’s unavoidable, spell them out.

It is permissible to spell out round numbers such as one hundred, thousand, million when they are being used to convey a rough order of magnitude rather than a precise count:

Thousands of people turned up to the event.

Quantities (numbers that apply to a unit)

Always use numerals for numbers relating to quantities (such as SI units or sums of money) or numbers on a scale, even when less than 10:

• It takes 8 minutes for sunlight to reach us
• A single dose of vaccine costs $3
• There are nine telescopes all in a straight line, set 2 kilometres apart
• A 2-kilogram meteorite was found in the garden
• The subjects gave the food a bitterness rating of 4 on a scale of 1 to 10

Avoid starting sentences with numbers attached to a unit

Large numbers and tiny decimals

For numbers above one million or below the decimal fraction 0.001 scientific notation may be more appropriate. This takes the form:

3 × 10¹⁵

Note: The multiplication symbol is not just a normal "x" on the keyboard. In HTML, it is written × so to display the example above would require: 3 &times; 10<sup>15</sup>

Be careful when converting large numbers from decimal to scientific notation, ensure you count the zeroes accurately:

See units.