It is generally best to write out numbers from zero to one hundred in nontechnical writing. In scientific and technical writing, the prevailing style is to write out numbers under ten. ... Numbers that are not conveniently round will read better written as numerals.

Should you spell numbers?

The general rule is that you should spell out numbers one to one hundred, and use digits for anything higher than that. Also hyphenate numbers that that are made up of two words (“thirty-seven”).

Is 100 written?

The Chicago Manual of Style recommends spelling out the numbers zero through one hundred and using figures thereafter—except for whole numbers used in combination with hundred, thousand, hundred thousand, million, billion, and beyond (e.g., two hundred; twenty-eight thousand; three hundred thousand; one million).