# Pound (lb) vs Pound (pd) **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [November 10, 2006, 4:57pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882 "2006-11-10T16:57:43Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![AlaninVancouver](https://avatars.discourse-cdn.com/v4/letter/a/a87d85/32.png) [@AlaninVancouver](https://boards.straightdope.com/u/AlaninVancouver)\ **Post date:** [November 10, 2006, 4:57pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/1 "2006-11-10T16:57:43Z")
Pound (lb) refers to mass. In outer space there is no “weight”. Pound (pd) is weight. So a pound of butter has no weight in outer space (0 lb) but weighs 1 pd on Earth. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [November 10, 2006, 5:24pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/2 "2006-11-10T17:24:52Z")
No. “lb” is the abbreviation for “pound”. “pd” is not. The avoirdupois pound is used as both a unit of mass and as a unit of force (weight is a force). If the “pound” is force, then the unit of mass is the “slug” – about 32 pound masses. If the “pound” is mass, then the unit of force is the “poundal” – about 1/32 pound weight. (More precisely, the number is 32.1740486, the standard acceleration of gravity on Earth in feet per second per second.) ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [November 10, 2006, 5:25pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/3 "2006-11-10T17:25:43Z")
I always use lbm and lbf to designate the difference. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [November 10, 2006, 5:44pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/4 "2006-11-10T17:44:35Z")
Welcome to the SDMB, Alanin. A link to the column is appreciated. Providing one can be as simple as pasting the URL into your post, making sure to leave a blank space on either side of it. Like so; [http://www.straightdope.com/classics/a3\_257.html](http://www.straightdope.com/classics/a3_257.html) ---
**Author:** ![Canadjun](https://avatars.discourse-cdn.com/v4/letter/c/76d3ee/32.png) [@Canadjun](https://boards.straightdope.com/u/Canadjun)\ **Post date:** [November 10, 2006, 8:31pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/5 "2006-11-10T20:31:06Z")
[QUOTE=AlaninVancouver] Pound (lb) refers to mass. In outer space there is no “weight”. Pound (pd) is weight. So a pound of butter has no weight in outer space (0 lb) but weighs 1 pd on Earth. [/QUOTE] Besides being wrong, as **John W. Kennedy** indicated, you contradicted yourself, since you claim that lb refers to mass, but then you say that a pound of butter is 0 **lb** in space. ---
**Author:** ![AlaninVancouver](https://avatars.discourse-cdn.com/v4/letter/a/a87d85/32.png) [@AlaninVancouver](https://boards.straightdope.com/u/AlaninVancouver)\ **Post date:** [November 11, 2006, 5:00pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/6 "2006-11-11T17:00:10Z")
Yes. I was lazy with my memory and didn’t edit my script. I meant that a pound of butter is 0 pd in space. And the word I forgot is “poundal” for pd–with reference to the force on a mass of 1 lb. Have I straightened it out for all, or have I missed something. My reference is a million years ago in high school physics. ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [November 11, 2006, 5:36pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/7 "2006-11-11T17:36:52Z")
Poundal is abbreviated to ‘pdl’. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [November 11, 2006, 8:12pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/8 "2006-11-11T20:12:05Z")
And a poundal is not the same thing as a pound weight. It is the force necessary to accelerate a pound mass at one foot per second per second, or, as I said earlier, about 1/32 of a pound weight. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [November 11, 2006, 9:02pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/9 "2006-11-11T21:02:04Z")
Well, this is all new to me. I’ve never seen “pd” meaning anything but “paid.” In that frame of reference, “ppd” means “post paid.” “Ppppththbbbb” is an expression of defiant disapproval, or a “Bronx cheer.” 😛 ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [November 12, 2006, 5:48am UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/10 "2006-11-12T05:48:17Z")
And the pound sterling (£) is the British unit of currency, which was when named the value of one Troy pound of silver (sterling). (Inflation has, obviously, changed that value.) A Troy pound, by the way, is, according to Wikipedia, 5760 grains (about 373.24 g, 12 troy ounces), while an avoirdupois pound is 7000 grains (about 453.59 g). It was used primarily for measurements of precious metals. ---
**Author:** ![Martini\_Enfield](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/martini_enfield/32/11123_2.png) [@Martini\_Enfield](https://boards.straightdope.com/u/Martini_Enfield)\ **Post date:** [November 12, 2006, 1:41pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/11 "2006-11-12T13:41:03Z")
The abbreviation “pd” or “pdr” is sometimes used when referring to British Field Guns- for example, the [25-pdr Field Gun](http://en.wikipedia.org/wiki/QF_25_pdr) (25 pounder, referring to the weight of the shell) is not generally abbreviated “25-lb field gun” (which would indicate a field gun which _weighed_ 25 pounds). Of course, the simple answer is for everyone to convert to the Metric System- including those slackers from the past. Just because it was OK in 1889 doesn’t mean you can keep carrying on about it now in your “history books” and what have you! 😃 ---
**Author:** ![Hsalf](https://avatars.discourse-cdn.com/v4/letter/h/c77e96/32.png) [@Hsalf](https://boards.straightdope.com/u/Hsalf)\ **Post date:** [November 19, 2006, 1:39pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/12 "2006-11-19T13:39:48Z")
Hi, All, The USA has been SI for measurements since the 1800’s. BTW, there is no longer a metric system, it is the Systeme International, or SI. What I mean is that all USA units are defined by SI units. The pound is 453.59238 g, meaning that the pound is a unit of mass. Abbreviated by lb. The unit of force in SI is the newton which relates to Newton’s law F=ma. If “a” is caused by an aceleration due to gravity, then “a” is replaced with “g”. There is a “standard gravity” used for gross measurements but in precision metrology (science of measurement) it must be measured at the place where the force is to be determined. Otherwise, standard gravity is a value determined at Potsdam. The value escapes my memory but since you are reading this on the Internet it should not be hard to find. So, in the customary system a pound is mass, or lb. A pound-force is lbf. I did mass measurements in a National Metrology Laboratory for 15 years so I hope I am right. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [November 19, 2006, 7:25pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/13 "2006-11-19T19:25:12Z")
It nevertheless remains true that in many engineering environments, the pound is a unit of force and the corresponding unit of mass is the slug, about 32 pound masses. ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [November 20, 2006, 3:42pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/14 "2006-11-20T15:42:36Z")
[QUOTE=Hsalf] BTW, there is no longer a metric system [/QUOTE] Ah, a jackbooted prescriptivist. 😛 If people call it the “metric system” then there is a metric system. ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [November 20, 2006, 10:29pm UTC](https://boards.straightdope.com/t/pound-lb-vs-pound-pd/379882/15 "2006-11-20T22:29:59Z")
Actually, there is a big difference between “metric” and “SI.” SI is a lot more anal. For example, volume must always be measured in cubic meters. No liters or mL. Also, you can’t use Celsius. Always Kelvin. No electron-volts, ergs, atmospheres, or molarity either. SI is strictly kilograms-meters-seconds. Another “metric” system is based on grams, centimeters, and seconds. In it, the unit of force, for example, isn’t a newton (kg_m^2/s^2) it is the dyne (g_cm^2/s^2). Seems in general use the word “metric” is more appropriate, as SI is something very specific. But what else can you expect from something whose name is just the words “international system” except always written in French?