# Usage of hyphens with numeric measurements

What is correct:

• two 1-Gb links;
• two 1 Gb links; or
• two 1Gb links?

I suspect the first, however I do not know the name of this situation, which makes it difficult to for me to find via Google. I have found some examples of typical units of measure (cm, inch, kg, etc.) but nothing for units such as Gb and KB -- I suspect they should follow the same rules, but in practice I rarely see such units hyphenated.

### Related

• This looks like a hyphenated compound modifier or phrase. Typically one adds a hyphen in cases where one feels there is going to be ambiguity. Nov 2, 2012 at 16:40
• The question should not refer to Gb and KB as binary units. An example of a binary unit is the KiB. 1 KiB = 10 000 000 000₂ (1 024₁₀) bytes. But 1 Gb = 1 000 000₁₀ bits, and 1 KB = 1 000₁₀ bytes. Nov 2, 2012 at 20:10

## 2 Answers

If you were spelling it out, you would write two one-gigabyte links, using a hyphen to create a compound modifier. However, a hyphen is not correct when using symbols.

With normal facilities available, don't use any sort of space: 1GB. This is the norm.

With non-lining proportional digits, that can put the 1 very close to the G, so where you can, you may prefer to use a thin space: 1 GB for example by employing an HTML entity `&#8201;`.

Two 1GB links (no space, normal use)
Two 1 GB links (thin space, might be preferred)
Two 1 GB links (normal space for comparison)

Different display methods may use a thin space which is more- or less-obviously thin.

Section 5.3.3 of The International System of Units states:

The numerical value always precedes the unit, and a space is always used to separate the unit from the number.

• @DaveJarvis I can see if I can find the relevant ISO standards or whatever, but it's the sort of thing that you pick up, remember and don't need to find again. Nov 2, 2012 at 17:37
• See en.wikipedia.org/wiki/… and reference 18. That mandates a space (so a hyphen is definitely not correct); I believe a thin space is preferable to a normal space. But no space at all is commonly seen. Nov 2, 2012 at 17:48

The closest thing to an answer I could find would be from the sixth edition of the APA manual.

# Section 4.31 — Numbers Expressed in Numerals

## (c) numbers that immediately precede a unit of measurement.

a 5-mg dose

with 10.54 cm of

The examples here differ in their usage but note one includes a mantissa (10.54 cm) and one doesn't (5-mg). Over in section 4.27 — Scientific Abbreviations (Units of Measurement) there are two examples given: 16–30 kHz

and

0.3, 1.5, and 3.0 mg/dl

Since none of these examples includes a hyphen I'd say you should go with either "two 1 Gb "or "two 1-Gb links". I'd steer clear of "two 1Gb".

• Um, so what exactly do you think that little horizontal line in "5-mg" is, if "none of these examples includes a hyphen"? Nov 2, 2012 at 21:44
• My mistake. I should have specified I was referring to {0.3, 1.5, 3.0} mg/dl when I said "none of these". I did not mean to include 5-mg. (These come from separate parts of the manual) I also found this diatribe to be useful and it is making me rethink my initial answer. link Nov 30, 2012 at 21:52