OK, the way I remember my high-school days back in the Pre-Cambrian, numerals from one to nine (and probably actually zero to nine) were to be spelled out. Anything over nine was to use numerals.
However, I also know that there are rules about consistency. For example, you should say “We went hiking, fishing, and hunting,” not “We hiked, fished, and went hunting.”
So, here’s the example that came up at work today: “This will take from six to 12 months.” It follows the rule, but it does shift from a spelled number to a numeralized number, when using the numeral “6” in this case would make it a little more fluid visually. Several of us who saw it had the same conclusion: “It looks a little strange, but that’s what the style guides say.”
The first example was the one that they settled on. Any dissent???
Huh. I seem to remember my teaching instructing us to spell out numbers 0-100, except in the case of age. Age you could write numerically. Of course, that was probably in middle school, which is a distant foggy memory, as old hells are wont to be.
It’s a question of style, not grammar, and how you do it depends on what style you are following (whether it comes from a style manual or you made it up [as in a house style]).
Chicago prescribes (generally) spelling out numbers from one to ninety-nine. However, if numbers representing similar quantities appear together and would be mixed (words/digits), use digits for all. So:
Yeah, examples like “six to 12” always bothered me, too. Until I started publishing my own publication. Then it seemed the only way to be consistent over the long haul. You might consider writing “six to twelve” instead of “6 to 12,” but when you get something like “six to two thousand, three hundred and twelve” it gets a little ridiculous.
The problem with setting up any style is balancing mildly annoying oddities like “six to 12” with the need for simply expressed and easily remembered rules that can be applied without constant recourse to the style book.
So the answer is, pick a style and stick to it.
FWIW, my style is to write out ten, too, since it’s such a small word. I start using numerals at 11.
Context is everything, too. It depends on what you’re writing and who your audience is.
If you are writing fiction, I can think of very few times where it is necessary to use a very long and precise number like 131,072. If this is intended to be character dialogue, especially, I would rephrase it to “over a hundred and thirty thousand.” But that’s just me: I don’t like seeing a block of Arabic numerals in a paragraph of prose. To my eye they stick out like ALL CAPS does. (Writing out the number the long way helps with timing, too. In Life, the Universe and Everything Zaphod plays a video game: “Congratulations,” it says, “you have scored seven points. Previous high score is three million, seven hundred and forty-two thousand…” This wouldn’t be as funny if you simply wrote the numerals because the eye would digest it too quickly. And hey, you wouldn’t write that the impossible odds the heroes face are 1,000,000 to one, would you?)
If you’re writing a business memo or a newspaper article, I would say that brevity and clarity win out over any kind of artistic posturing; numerals would be preferred precisely because they do stick out and are extremely precise. The purpose of those kinds of communications is to be precise and report facts.
But yeah, I’d say not to mix the styles if it can be helped in “6 to twelve.”