When writing numbers in papers, the general rule of thumb is to use numerals for numbers 10 and above, and to spell out numbers below 10 (unless they are part of a larger number, such as 12). You should also use numerals for measurements (such as 4 inches) and for dates (such as December 5). Additionally, for large numbers, it is often better to use numerals rather than spelling them out (such as 1,000 versus one thousand).