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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."?

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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. –  Jon of All Trades May 3 '13 at 19:26
    
@JonofAllTrades "5 lbs." (or similar) is far superior when it comes to signage, though. –  Alex P May 4 '13 at 1:11
    
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 4 '13 at 9:00
    
@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 6 '13 at 1:22
    
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 at 23:13

4 Answers 4

up vote 6 down vote accepted

In scientific publications, units of measurement are 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.

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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 3 '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 4 '13 at 5:52
    
@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 4 '13 at 15:58
    
@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 5 '13 at 17:25
    
@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 5 '13 at 18:23

"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.

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Perhaps you should read this Wikipedia article which says: "The commonly used abbreviation lbs to indicate the plural unit of measurement does not reflect Latin usage, in which lb is both the singular and plural abbreviation." –  Manish Aug 14 at 6:06

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.

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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 3 '13 at 18:36
    
@BraddSzonye, fixed kg –  jwpat7 May 3 '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." –  Jon of All Trades May 3 '13 at 19:25
    
This could be grossly misleading. nGrams need to be handled with extreme discretion. –  Kris May 4 '13 at 5:54
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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. –  jwpat7 Nov 19 '13 at 4:04

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.
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Worth adding that metric units are never pluralised. Half a pound is 227g, not 227gs. –  Andrew Leach May 3 '13 at 18:47
    
@AndrewLeach Plural abbreviations are rare even in English units: lbs is one of the few exceptions. Thanks for the suggestion, I updated the answer. –  Bradd Szonye May 3 '13 at 18:49
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@AndrewLeach, only if we are talking about avoirdupois. If troy is intended, then half a pound is 186.5 g. ;-) –  Janus Bahs Jacquet Aug 2 '13 at 10:42

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