Put a nonbreaking space between the number and the unit.
Spaces in units of measurement
For most units of measurement, when you specify a number with the unit, use a nonbreaking space between the number and the unit. This guidance applies in both HTML and Markdown.
For guidance about when to spell out units, see the Abbreviations page.
Recommended: 64 GB (64 GB)
Recommended: 25 mm (25 mm)
Not recommended: 64 GB
Not recommended: 64GB
However, when the unit of measure is money or percent or degrees of an angle, don't use a space. For more information, see Currency.
Recommended: $10
Recommended: £25
Recommended: 65%
Recommended: 180°
For degrees of temperature, don't use a space before the degree symbol, but do use a nonbreaking space between the degree symbol and the abbreviation for the temperature scale (F or C). For Kelvin temperatures, leave out the degree symbol but use a nonbreaking space before the K.
Recommended: 50° C (50° C)
Recommended: 300 K (300 K)
When a number and unit of measurement combine to modify a noun, don't hyphenate unless the hyphen is needed for clarity.
Recommended:
200 GB disk (200 GB disk)
Ranges of numbers with units
In a range of numbers, repeat the unit for each number. Unit includes both symbols (like the degree symbol (º)) and abbreviations (like MB for megabytes) but not nouns (like file). For more information, see Range of numbers.
Use the word to between the numbers, rather than a hyphen. A hyphen can be misinterpreted as a subtraction sign.
Recommended: -40° C to 85° C
Not recommended: -40-85° C
Hyphens with multiplied units
When the components of a unit of measurement are multiplied by each other, hyphenate them.
Recommended: 5 vCPU-hours
Recommended: 40 person-hours
Use k to indicate thousands
In some contexts, it might be appropriate to indicate thousands of something by following a number with a lowercase k. If you do that, then follow these guidelines:
- Don't put a space between the number and k.
- Add a noun to indicate what the number measures, and to make clear that you're not using k as an abbreviation for kilobytes.
Recommended: On this plan, you are limited to 55k download operations and 20k upload operations per day.
Currency
If you're writing about monetary amounts, make sure that the reader knows what currency you're referring to. For example, the dollar sign—the $ symbol—can refer to US dollars, Canadian dollars, Mexican pesos, and several other currencies.
If there's any possibility of ambiguity, use a currency indicator before the amount. For details, see section 9.20 and following in the Chicago Manual of Style, 17th edition.
Recommended: US$10
Rates
Use per instead of the division slash (/) when space permits. It's OK to use the division slash when space is limited, such as in a table with small cells.
Shorten per to p only for well-established abbreviations for rate units, such as Gbps for gigabits per second or MBps for megabytes per second.
Recommended: requests per day
Not recommended: requests/day
Recommended: Gbps
Not recommended: Gb/s
Decimal and binary units
Use the same system to measure bytes as the technology that you're documenting. Don't use MB if you mean MiB, or GB if you mean GiB. The following table lists common types of decimal and binary units:
| Decimal units | Binary units |
|---|---|
| kB (kilobyte, or 1000 bytes) | KiB (kibibyte, or 1024 bytes) |
| MB (megabyte, or 10002 bytes) | MiB (mebibyte, or 10242 bytes) |
| GB (gigabyte, or 10003 bytes) | GiB (gibibyte, or 10243 bytes) |
For more information about abbreviating measurement terms, see When to spell out a term.
Provide visuals for math concepts
Accompany math concepts and numerals with diagrams or other images to support comprehension. For example, if comparing statistics, consider illustrating percentages in a pie chart or a bar graph.
Accompany numerical concepts with real-world practical implications
Accompany numerical concepts with real-world practical implications to provide tangible meaning. For example, if using a feature incurs additional fees, add a link to pricing calculator.