How to Write Numbers:

The most important thing is that you keep what you do consistent.

  Also use your best judgement when writing numbers in dialogue. 

Years

• Spell out centuries
• twenty-first century
• Use apostrophes to show missing numbers
• always angled to the left ′70
• Use numerals for dates
• September 17, 2012
• Don’t use apostrophes for plural years
• 1920s

Spell Out

• If followed by hundred, thousand, hundred thousand
• Any number that comes at the beginning of a sentence
• work it so years don’t end up here
• Always write out centuries
• Measurements
• unless it’s normally seen as a numeral, 50 gallons
• Simple Fractions
• unless mixed with whole numbers
• Monetary Values
• unless it’s complicated or a lot of values in one paragraph
• Times followed by o’clock and half-hour or quarter times
• unless it’s specific: 4:18
• don’t use numerals for midnight or noon
• Spell out numbered streets up to 100

Use Numerals

If followed by million, billion, etc

If a complicated number

• 54,321 instead of spelled out

If there are a lot of numbers in one paragraph

Abbreviated unit of measurement

• 50 mph
• no numeral then spell out the measurement

Percentages

• if using % no space between numerals and symbol

For pages, chapters, volumes, verse numbers, illustrations, and tables