Rules for Numerals

When are numbers written out, and when are they used as figures?  Here are a few general guidelines:

• A number at the beginning of a sentence is written out.  Example:  Eighty-four thousand dollars are in the bank.

• Ages are expressed as figures.  Example:  She was 35 years old.

• Dates usually spell out the month and then express the day and year as figures.  Example:  September 10, 2008.

• Numbers under 10 are written out, while numbers of 10 or more are expressed as figures.  Example:  He read chapters one through nine, but only skimmed chapters 10 through 20.

• Time of day is usually expressed in figures. When followed by “o’clock,” though, spell it out.  Example:  It was four o’clock in the afternoon. This was only 15 minutes later than 3:45 p.m.

• Percentages usually use figures.  Example:  The average was 25%.

• Measures and weights use figures if the unit is abbreviated, but if the unit is spelled out, then spell out the number, too.  Example:  The measurement was fifteen cubic feet (15 cu ft).

• Monetary units use figures, but if the amount is a round number, it’s not necessary to use “00.”  Example:  He had $12, but she had $12.15.

• Round numbers use figures for the amount, but may spell out the units.  Example:  The firm made a $10-million-dollar profit (or a profit of $10 million).

• Ordinals (the “th” form) usually use figures.  Example:  It was the 24^th of the month.

• Numbers of four digits or more have each set of three digits separated by a comma.  Example:  There were 6,580 pieces in the set.