Is 1 LB (pound) always by weight or by measure?

Do you guys generally call one LB (of say DME or grain) 16 oz (in a measuring cup), or 1 actual pound of weight on your precision scale?

Weigh it, volume doesn't work.

Weight and volume are not the same thing....You weigh the dry goods

The scale doesn't have to be 'precision' per say... a cheapo food scale will work for grains and generally hops

There are fluid ounces and weight ounces. Weight measures weight, fluid ounces measures volume. There are 16 weight ounces in a pound. There are APPROXIMATELY 16 fluid ounces of water in 1 lb of water, (but not exactly). LME weighs much more, so there are FEWER than 16 fluid ounces in 1 lb of LME, (but still 16 weight ounces). DME weighs less, so there are MORE than 16 fluid ounces of DME in 1 lb of DME. You need to know the density of a certain thing, (and how well it's packed, if it's a solid like DME), to convert between fluid ounces and weight ounces.

To sum up:
1 lb DME = 16 ounces DME
16 ounces DME = MORE than 16 fluid ounces DME
1 lb LME = LESS than 16 fluid ounces LME
1 lb water = ABOUT 16 fluid ounces water.

Thanks guys. It sounds like if I actually weigh the DME, grains, hops, invert sugar, etc I'll be ok. I have a nice (but inexpensive) digital scale that does grams, oz, lbs, klgs up to 8 lbs as small as 1 gram.

shortyjacobs said:

To sum up:
1 lb DME = 16 ounces DME
16 ounces DME = MORE than 16 fluid ounces DME
1 lb LME = LESS than 16 fluid ounces LME
1 lb water = ABOUT 16 fluid ounces water.

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Except I've never seen a "fluid" oz of dry malt extract....

mmb said:

Except I've never seen a "fluid" oz of dry malt extract....

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Yup, I know....fluid ounces are traditionally only used for, well, fluids...but they are a valid measurement of volume, and hence could be used for dry things. Like I said, there's only meaning to it if you include density or packing fraction.

A "pound" is a measure of weight, period.

TexLaw said:

A "pound" is a measure of weight, period.

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Except when it a unit of currency. You would think they could come up with some other words instead of re-using all the same ones.

My wife still doesn't understand when she's cooking something that calls for ounces and I ask her what she's measuring because it could make a difference if she needs fluid ounces or by weight. She just looks at me like I'm speaking another language.

TexLaw said:

A "pound" is a measure of weight, period.

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Surprisingly it isn't, at least in engineering terms.

This is pedantic, but in order to use Imperial units in engineering calculations, (which is ridiculous, because any engineer worth his/her salt uses SI), lbf and lbm have to be invoked. The definitions are slightly circuitous, but 1 lbm, (or pound-mass), is the amount of matter that weighs 1 lbf (pound-force) under an acceleration of 32.2 ft/s^2, (9.81 m/s^2, the acceleration of gravity at sea level). 1 lbm is therefore equal to 454 grams. The force exerted on 454 grams, or 1 lbm, at sea level by gravity is equal to 1 lbf, or 454 grams * 9.81 m/s^2, or 4.45 kg*m/s^2, or 4.45 Newtons.

When we say "lb", we usually mean "lbf", since we are usually talking about force on earth. 1 lbm under a different gravitational field, however, (say on Mars or the Moon), will weigh a different amount in lbf, (Less, in these cases). Similarly, 1 lbm that is being accelerated at 2 gravities, (around 64.4 ft/s^2), will weigh 2 lbf.

It's worth noting that "weight" is defined as "force on a mass due to acceleration", so if something "weighs" 1 lb, it means that it could be 1 lbm under 1 g acceleration, or 0.5 lbm under 2 g acceleration, or 2 lbm under 0.5 g acceleration, or any other ratio you care to consider.

tl;dr: "lb" can mean either "lbf" or "lbm", force or mass, depending on context.

(sorry for the )