How to Write Numbers
When do you write out numbers (and why do they call it “maths” in England)?
Sometimes Math Dude, one of the other Quick and Dirty Tips podcast hosts, gets questions that are more about writing than they are about math, so today, I’m going to answer some of those questions.
How to Write Numbers
People get confused about how to write numbers because different style guides make different recommendations, so it’s easy to hear different rules from different people.
In general, the Chicago Manual of Style wants you to write out the words for more numbers than other style guides. For example, the Associated Press and the British newspaper the Guardian both recommend that their writers use the words for numbers less than 10 and the numeral for anything bigger:
Today, firefighters rescued nine cats from trees.
Yesterday, firefighters rescued 11 cats from trees.
But the Chicago Manual of Style recommends recommends using the words for all whole numbers 100 and lower, and also for big round numbers such as one thousand and twenty thousand.
Today, local firefighters rescued nine cats from trees.
Yesterday, local firefighters rescued eleven cats from trees.
Last year, local firefighters rescued forty-seven cats from trees.
Last year in the US, firefighters rescued 728 cats from trees.
Last year worldwide, firefighters rescued more than one thousand cats from trees.
There are a huge number of exceptions to these rules. I covered some of them in episode 100, but if questions about numbers come up a lot for you, you really need to get a style guide and look it up. The Chicago Manual of Style has a whole chapter just on numbers.
Next: How to Write Fractions
How to Write Fractions
Fractions are even more complicated than whole numbers.
First, you have what some sources call the “simple fractions.” These include ½, ¼, ¾, and so on, and most sources want you to spell out these fractions in text. In most cases, you use a hyphen with the words, so you’d write “two-thirds” and “three-quarters.”
However, style guides still differ once we go beyond simple fractions, and this time it’s the Associated Press that wants you to spell out everything. They recommend spelling out all fractions less than one, but the Chicago Manual of Style wants you to convert anything that isn’t a simple fraction to decimal form. So you’d write “five-sixteenths” for the Associated Press, but you’d convert it to 0.3125 for the Chicago Manual of Style.
Of course, the Associated Press also says that if you’re using lots of unusual fractions, you should consider converting them to decimals. So one or two “five-sixteenths” and “seven-fifteenths” are fine, but if you have lots of them, convert them all to decimals.
Again, there are lots of exceptions. For example, even though you should write out fractions in text according to the Guardian, you still use the figures in tables and recipes, and the Chicago Manual of Style also notes that the rules can be different for technical documents.
The Associated Press says if you’re writing the numerals for a whole number with a fraction—like 2 ½—you leave a space between them. The Chicago Manual of Style says no space.*
One final word on fractions: the Guardian style guide makes the excellent point that you should try to avoid mixing fractions and percentages in the same story. Stick with one format.
“Math” Versus “Maths”
I can’t give you an answer about why it’s “math” in the US, but “maths” in the UK, but I can give you some history.
Of course, both “math” and “maths” are a short version of the word “mathematics.” It comes from the Latin “Mathematica.” It’s plural in Latin, which is why it has the “s” on it in English, but we treat it as singular.
That change from plural to singular happens sometimes with Latin words that come into English. For example, “agenda” is plural in Latin, but we treat it as singular in English. So it’s not that unusual that “mathematics” is singular.
In both British and American English, the early uses of “math” and “maths” were followed by a period, indicating that they were abbreviations for “mathematics.” It looks like Americans abbreviated it first, because the first example of “math” in the Oxford English Dictionary is from 1891, and the first use of “maths” comes later in 1911.
It was only over time that they both became words in their own right instead of being considered abbreviations and started appearing without the period at the end.
*Note: This paragraph originally incorrectly stated that Chicago requires a space between a whole number and a fraction.