### 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. Numbers with five digits take a comma 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 × 10 ^{15}*

*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 × 10<sup>15</sup>`

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

Decimal notation |
Scientific notation |

6,720,000,000 | 6.72 × 10^{9} |

0.000 000 007 51 | 7.51×10^{−9 } |

9,130,000,000,000 | 9.13×10^{12} |

See **units.**