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What is the correct way to say: "All items over 5 lbs. are excluded." I'm specifically asking about "lbs." or is it "lb."? American English if it matters.

Also is "5lbs." ever correct? Or is it "5 lbs."?

RegDwigнt
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orange80
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    Assuming it's not casual usage, I'd recommend "All items over five pounds are excluded," instead. Most style guided recommend spelling out numbers of ten or less, and in such a case I'd spell out the unit, too. –  May 03 '13 at 19:26
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    @JonofAllTrades "5 lbs." (or similar) is far superior when it comes to signage, though. – Alex P May 04 '13 at 01:11
  • I am amazed that there can be such spirited debate over whether a period can follow an abbreviation and no-one notes that pounds is NOT a unit of weight! Did the OP mean to refer to mass? – Fortiter May 04 '13 at 09:00
  • @Fortiter In case the copy text I provided was not enough of a clue, I was just double-checking this for some copy that will go in an e-commerce shopping app. It's not my job at all to check this, but what someone had wrote for the "5 lb" part looked totally wrong, so I wanted to make sure. – orange80 May 06 '13 at 01:22
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    Pounds does not only refer to mass. It also refers to the weight that one pound of mass weighs on the earth. See the Wikipedia entry on Pound (Force). – Henry74 Jul 14 '14 at 23:13

4 Answers4

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In scientific publications, units of measurement are almost never pluralized when abbreviated. This should remain true for general use, as well. You should therefore never write "lbs." You should technically not need a period after "lb" either, unless it's at the end of a sentence.

The abbreviation "lb" comes from the Latin libra, which is itself short for libra pondo, or "pound weight." And in any case, the plural of libra would be librae, not libras.

And, again in scientific papers, there is always a space between the quantity and the unit.

Dmitry Brant
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    Agreed that 5 lb is correct for scientific usage, but 5 lbs. is common in general English, and some style guides require the period. Please don't recommend “never” for general use without evidence from a general English style guide. – Bradd Szonye May 03 '13 at 18:24
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    @BraddSzonye & esp., the up voters : Like to know of any style guide that recommends "All items over 5 lbs. are excluded." with a pluralized lbs. Never make a universalized comment. And do not up vote just to show your ignorance. – Kris May 04 '13 at 05:52
  • @BraddSzonye I don't think Imperial (or 'English' if you're in the US) units find much currency in any kind of scientific literature. The use of metric is near universal. Might prove difficult to find any kind of contemporary example! – Marko May 04 '13 at 15:58
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    @Marko The questioner asks about “American English,” not scientific literature, which is why I have reservations about this answer. Metric usage is far from universal here. – Bradd Szonye May 05 '13 at 17:25
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    @Kris I don't think anyone suggested that style guides recommend pluralized lbs (although it's common in actual usage). I was noting that some guides require the period when abbreviating English units (lb. versus lb). – Bradd Szonye May 05 '13 at 18:23
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Grammar Girl has a related article, “Units of Measure.” The key points:

  • Put a space between numbers and units of measure. Typographers prefer a thin space, but you shouldn't generally need to worry about it.
  • Abbreviations are generally the same for singular and plural units: While lbs isn't incorrect, lb is better for formal and scientific use. Never pluralize metric system units like meters and grams.
  • Period usage varies with style guide. They're more common in American writing. However, never use periods with metric system units.
Bradd Szonye
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I suggest writing 2.3 kg instead of any of 5 lbs., 5lbs., 5 lb. or 5lb. Historically, however, the forms “5 lb” and “5 lbs” appear to have been used more than either of the others (according to ngrams for 5 lbs,5lbs,5lb,5 lb,5 lb . [where 5 lb . represents 5 lb. ie has a period after lb as part of the search]) : ngrams of 5 terms

Note, if you click on the book links on the ngrams page, you will note that in many instances the 5 is after a decimal point, eg, “12.5 lbs.”.

Note, naturally 5 lb occurs more often than other forms because 5 lb occurs in every instance of any of {5 lbs, 5 lb, 5 lb., 5 lbs.}. Ngrams for 5 lbs,5 lb,5 lb .,5 lbs . shows that 5 lb. and 5 lbs. nowadays occur with nearly equal frequency, the latter slightly more frequently. Before 1980, 5 lb. occurred rather more frequently than 5 lbs.

James Waldby - jwpat7
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    2.3 kg is not appropriate for general use in American English, and 2.3 Kg (with capital K) is incorrect everywhere. Helpful Ngram though, thanks! – Bradd Szonye May 03 '13 at 18:36
  • @BraddSzonye, fixed kg – James Waldby - jwpat7 May 03 '13 at 19:14
  • Note that this Ngram does not validate that "items over 5lb are excluded" is valid. "5lb" (or, better, "5 lb" or "5-lb") is valid as an adjective. So most of these instances are something like "get a 5lb bag of flour." –  May 03 '13 at 19:25
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    This could be grossly misleading. nGrams need to be handled with extreme discretion. – Kris May 04 '13 at 05:54
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    @FumbleFingers – I updated figure. Yes, 5 lb occurs structurally in all of {5 lbs, 5 lb, 5 lb., 5 lbs.} so is most common, but as noted in ngrams in last paragraph of answer 5 lb. now occurs less often than 5 lbs. – James Waldby - jwpat7 Nov 19 '13 at 04:04
  • Is this correct, then, if I chose to abbreviate? My uncle weighs 350 lb. (Not: 350 lbs.) – whippoorwill Feb 25 '14 at 17:34
  • @whippoorwill, either form is ok; use whichever you like. The lbs form's frequency of use is increasing. – James Waldby - jwpat7 Feb 25 '14 at 19:40
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"lbs" is never correct, lb is an abbreviation for Libra (Latin for Balance/Scales), and is both singular and plural it should always be lb.

Rob
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