Except for whole numbers used in conjunction with hundred, thousand, hundred thousand, million, billion, and beyond, the Chicago Manual of Style suggests writing out the numerals zero through one hundred and using figures after that (e.g., two hundred; twenty-eight thousand; three hundred thousand; one million). Some writers prefer writing out only those numbers that are commonly used (zero through nine), but most use figures as well for numbers between ten and one hundred.
Writers may want to follow their own style guide when it comes to how many digits should be written out when numbering sentences, paragraphs, or pages. Many print styles require that numbers be written out in full, while others allow for some shortening of very large numbers. Your best bet is to look at examples of numbers in the book you're writing to see what format they are written in.
For example, if I were quoting the number 28,000 in text, I would write "thirty-eight thousand". If the number was not quoted, I might write about it occurring several times in the text without naming it, thus leaving it up to the reader to infer its quantity - perhaps there are several thousands of them? In this case, I would write about it being "a large number".
In nontechnical writing, it is often better to write numbers from 0 to 100. The dominant technique in scientific and technical writing is to write out numbers less than 10. While there are exceptions to these guidelines, your primary focus should be consistently expressing numbers. Readers understand that you are counting, so they do not need to be told this fact by using words like "a", "an", or "the".
If you must use words instead of symbols, then write out the number in words as well as digits. This makes it clear to the reader what method you are using to count. For example, instead of saying "I wrote a word and a half on my notebook," say "I wrote a letter and a half on my notebook."
As another example, say "I visited five countries" instead of "I went on a trip of five countries."
Finally, if you have lots of things to count, make sure that you do not run out of digits early. For example, instead of saying "I counted 50 cookies" say "I counted 50/10 = 5 bags of cookies."
On average, people can count up to 20 before they start mixing numbers together. If you want to express a number greater than 20, then you will need more digits than just ones and zeros.
Whether or not to use figures (also known as numbers) is mostly a question of personal taste. The methods of America's two most important style and usage guides differ: The Associated Press Stylebook suggests writing out the digits 0 through 9 and then using numerals until one million is achieved. The Chicago Manual of Style prefers writing out the whole number and then using numerals.
When writing numbers larger than nine, use figures. When writing numbers smaller than nine, use figures. This is because computers are programmed to recognize figures for numbers less than ten and all other characters for numbers greater than ten. Thus, if you want your document to look like everyone else's document, use figures for all numbers.
Figures are used in mathematics and scientific writing to show large numbers. For example, "five figures" means five digits, also called florets. When writing about science experiments, researchers usually specify the figure used in their experiment. For example, an experiment may be described as producing a result with "five figures accuracy." Scientists consider three or more figures to be accurate enough for research purposes.
Figure numbers can be expressed as words or as symbols. Words are usually written out in full, except for the first figure and last figure numbers. Symbols are commonly used in mathematics and physics papers to represent large numbers.
Here are some examples of numbers that contain zeros.
For higher numbers, depending on the context, you can use either digits or words (e.g., a thousand people or 1,000 people), but in technical writing, you should always use figures, e.g., 200,000 km. The written form is preferable for bigger but less exact figures (e.g., several thousand).
Figures are usually represented as numerals: 200,000. But if there's no way to show all the digits, then letters can be used instead: 2000K. Or even words in some languages: 20M.
In English, only three ways remain to express large numbers: figure out what kind of symbol will be understood everywhere, use mathematical notation such as 10⁹, and say it aloud!
Figure out how much memory your computer has and divide that number by 1000000 to get the size of its cache in MB. If the result is not a whole number, then your computer has some MB reserved for caching data that won't be used later, which could mean that you have to wait before your programs start up. If this happens often, you might want to upgrade your computer's memory or swap space.
We can also refer to the number of digits for basic generalizations. For example, because 10,000 has five digits, we refer to it as being in the tens of thousands, but it may also be referred to as a five-figure number... In English, saying a lot of numbers.