Weights (Avoirdupois) Weights (Troy and Apothecaries) Jewels Rough conversion
   between Imperial and Metric

Weights (Avoirdupois)

Units of weights
16 dram = 1 oz
16 oz = 1 lb
14 lb = 1 st
2 st = 1 qtr
4 qtr = 1 cwt
20 cwt = 1 ton
oz - ounce
lb - pound
st - stone
qtr - quarter
cwt - hundredweight



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Select other units for conversion.

The abbreviation for hundredweight is "cwt" because "C" is the Roman symbol for 100. It is called a hundredweight because it is 112 lb (well, it's close!). It can also be called the long hundredweight to distinguish it from what the Americans call the short hundredweight, which is 100 lbs. So the long ton or UK ton is 2240 lbs, and the short ton is 2000 lbs. The metric tonne is 1000 kg (about 2205 lbs). The word "ton" is derived from the same source as that of a tunne of wine, a cask which held about 250 gallons. Tons were in use in the late 15C.

Standard weight and measure Cities in England would have official standard weights and measures. Merchants weights and measures would be checked against this to make sure they weren't trying to cheat their customers! These are a standard weight and measure from Manchester both dated 1754 and made of cast brass. They are now in the Museum of Science and Industry in Manchester.

A dram is short for a drachm, but since the avoirdupois drachm is different from the apothecaries drachm, it could be that the name "dram" was used to help distinguish it. These different types of weight measurement are a confusion anyway. The kilogram is at least well defined without having to say which system you're using! Scots use 'dram' to mean a small glass, probably of whisky! I don't think this is connected with the weight measurement dram.

A pound is always written as "lb" to prevent confusion with pound money "£". It is very old, traced back to the Roman "libra" (which explains its abbreviation!). It was defined in England since Ethelred the Unready (968-1016). In fact, a pound (money) was originally a pound (weight) of silver, and the symbol for pound (money) £ is a stylised L.

The abbreviation for ounce is "oz". This comes from 15th century Italian, also "oz" which is an abbreviation of "onza". "Oncia" seems to be the modern Italian for ounce (although they use metric measures now, of course) and I suppose that "onza" is a variant of this. The word "ounce" comes from the Latin "uncia" or twelfth part. The ounce is a sixteenth part of a pound avoirdupois, but it used to be a twelfth part of a pound troy. Troy weights are now only used for precious stones and metals (and not even for that, much), but they used to be the normal measure of weight. See a Tudor set of measures.

Weighing scales Old fashioned scales had metal weights which were balanced against what you were weighing (see right).

Winnie the Pooh wrote a poem about Tigger:
     "But whatever his weight in pounds, shillings and ounces,
      He always seem bigger because of his bounces."
Piglet didn't think that the shillings ought to be there, but Pooh explained "They wanted to come in after the pounds, so I let them. It's the best way to write poetry, letting things come." (The old sterling money (pre-decimal) was £.s.d or "Pounds, shillings and pence".)

Rob (aged 11) has pointed out that, strictly speaking, lb and oz measure mass, not weight. However, the old school books had tables on the back of them headed 'Weights and Measures', so since this is really a history website rather than a scientific one, I'm afraid that I shall continue to use the word 'weight'! Rex adds to the debate by saying "Pounds measure force, not mass (a weight is a force). The unit of mass in the Imperial system is a ridiculous unit called a "slug," which weighs 32 pounds avoirdupois under standard conditions. I've had further correspondence about this, which has led me to do a little research (well, I've googled a page or two!) There does seem to be a confusion here. When I did Physics A level in 1970, we were taught that pound (lb) was a unit of mass, wheareas pound weight (lb wt) was a unit of weight. However, says that the pound or pound-force is the unit of weight and the pound-masses is the unit of mass, although slugs are more used. However here, they admit that different authors use pound for either mass or weight. I suspect that this is a difference between American and British usage. The British obviously decided that if they were going to buy apples on the Moon, then they wanted a pound of apples to contain the same number on Earth, so it should be mass. The Americans said rather that they wanted a pound of apples to feel the same on the Moon as the Earth, so it should be force. Personally, I refuse to buy a slug of apples wherever I am!
A further American comment: "In my experience, the folks who insist that pounds are always a unit of force tend to be the physics students (probably to make F=m*a easier on first-semester students) while the engineering students will use pounds more as a mass. Ultimately, Congress defined the pound in terms of grams (not Newtons) in the 1890's, and in the 1950's the remnants of the foot/pound using world got together and standardized on the same number of grams, so "pound" is definitely a unit of mass. Of course, there's still "pounds of force" used, abbreviated "lbf," but that has to be differentiated from "regular pounds." When you think about it, it makes sense that the pound, like the kilogram, is a unit of mass. The standard has always been a solid object, and in order to compare what you want to know the "weight" of in terms of this standard, you'd have to use a beam balance, which ultimately measures mass. The slug, as I mentioned before, is simply a convenient unit to use so that it takes 1 lbf to accelerate it 1 ft/s^2. Before non-SI metric units fell into disuse, there was a similar unit called the "hyl," where 1 "kilogram of force" would be enough to accelerate it 1 m/s^2."

Wool used to be measured in tods. A tod was 28 lbs, or 2 stone. For some reason, the plural of stone is also stone - like sheep, come to think of it!

Coal on Tyneside was measured in chaldrons of 53 cwt, and keels of 8 chaldrons or 21 tons 4 cwt. There were 8 Newcastle chaldrons to 15 London chaldrons. A London chaldron contained about 28.5 cwt or 36 heaped Winchester bushels. There was plenty of scope for misunderstandings in the coal trade 200 years ago.

Lead was worked in bings containing 8cwt of clean ore. The ore was refined into pigs of 1.5 cwt, and these pigs were sold by the fother containing 14 pigs for a total of 21 cwt. Silver was recovered from the lead at about 8 ozs per fother, although in the Alston area about 42 ozs of silver per fother were recovered.

Americans measure their own weight in pounds rather than stone. So here is a conversion table.

1 st = 14 lb
2 st = 28 lb
3 st = 42 lb
4 st = 56 lb
5 st = 70 lb
6 st = 84 lb
7 st = 98 lb
8 st = 112 lb
9 st = 126 lb
10 st = 140 lb
11 st = 154 lb
12 st = 168 lb
13 st = 182 lb
14 st = 196 lb
15 st = 210 lb
16 st = 224 lb
17 st = 238 lb
18 st = 252 lb
19 st = 266 lb
20 st = 280 lb

An email from a 60 year old from Dallas, Texas, said: "We still sell berries by the pint in this country, but potatoes are sold by the pound. Potatoes used to be sold by the peck. If my parents were alive they would be 100 and 101. Since I haven't bought nails in years, I don't know how they are sold in bulk rates today. When I was a child, my father would send me to the hardware store by 10 penny nails by the pound. Today they are sold in plastic bubble packages."
In Britain, we still sometimes buy prawns and shrimps by the pint, but I've not heard of fruit being sold that way. Strawberries are often sold by the punnet (a small cardboard basket), but most berries are sold by weight. Potatoes were sold by the pound, or stone if you bought enough. Now it's all kilos, of course.

Weights (Troy and Apothecaries)

Troy Weight
24 grains = 1 pennyweight
20 pennyweight = 1 troy oz
12 troy oz = 1 troy lb
Apothecaries Weight
20 grains = 1 scruple
3 scruples = 1 drachm
8 drachms = 1 apothecaries oz

Troy weight is a system of weights used for precious stones and metals. The troy pound is no longer in legal use, but gold is still sold in troy ounce bars. Apothecaries weight was used for measuring drugs and medicines. Both systems had the grain, ounce and pound in common (since a troy ounce was the same as an apothecaries oz).

A pennyweight was called that because it was the weight of a silver penny.

A scruple is derived from the Latin for a small stone, because it's a very small weight. We also use scruple to mean your conscience pricking you like a small sharp stone in your shoe!

These weights were not learned at school, because they had very specialised use. But our normal weights tables were always marked as avoirdupois (which comes from Old French "to have weight"). The troy system dates from the 10C. The troy pound was defined as different from the avoirdupois pound in the reign of Elizabeth I (1558-1603). See this Tudor set of measures, where the table defines troy weights, and then separates avoirdupois and troy weights without giving the conversion factor!

1 troy oz = 480 grains
1 troy lb = 5760 grains
1 oz avoirdupois = 437.5 grains
1 lb avoirdupois = 7000 grains

There is an old joke "Which is heavier, a pound of lead or a pound of feathers?" Of course, they weigh the same. But if you said "Which is heavier, a ounce of gold or a ounce of feathers?", then you could claim that the gold is measured in troy and the feathers in avoirdupois, and so the gold is indeed heavier. But a troy pound of gold is lighter than a pound (avoirdupois) of feathers!
The weight of feathers in a vacuum is different than those same feathers at STP (buoyant force, Archimedes' Principle). In fact, if you took a pound (mass) of lead and feathers, and weighed them on scales (on Earth, which has an atmosphere), the lead would be heavier. This is because the feathers displace more air (for non-scientists, something similar to what makes things float.)
The original joke depends partly on getting weight and volume muddled up. However, we also know that if you dropped a feather, and a piece of lead, the feather would take longer to drop as it would float off to one side then the other. This is because of air resistance. One of the experiments when men went to the Moon was to drop a feather and a piece of lead together. It looked extremely strange to see them drop at the same speed!

Jewel weights

Troy weight (see above) was used for precious metals and stones. But individual stones may be described using carats.

200 milligrams = 1 carat
100 points = 1 carat

Carat is derived from "quirrat", Arabic for the seeds of the coral tree, which were the traditional weights for precious stones.

There is a different meaning for "carat". 24 carat gold is pure gold. 18 carat gold is 18 parts of gold to 6 parts of other metals. 9 carat gold is mostly something else!. The Americans spell this measure of purity "karat" to distinguish it from the other sort of carat.

Rough conversion between Imperial and Metric

I find many Imperial to Metric conversions very irritating, because they are far too precise. So here are some rough conversions which you can carry in your head.

A smartie weighs about a gram.

A pack of butter weighs 250 grams or a quarter of of kilo.

A bag of sugar weighs a kilo.

If you're buying fruit and veg, then (very roughly) 1lb is half a kilo.

Here is a mnemonic for remembering weight imperial to metric conversion:

"Two and a quarter pounds of jam weigh about a kilogram" (or of course anything else!)

Here is a rough conversion chart:

Accurate to
10gms up to 1lb 8oz
and 20 gms above
1 oz = 30 gm
2 oz = 60 gm
4 oz = 110 gm
8 oz = 230 gm
12 oz = 340 gm
1 lb = 450 gm
1 lb 4 oz = 570 gm
1 lb 8 oz = 680 gm
1 lb 12 oz = 800 gm
2 lb = 900 gm
Accurate to
1/2 oz up to 1 lb
and 1 oz above
100 gm = 3.5 oz
200 gm = 7 oz
300 gm = 10.5 oz
400 gm = 14 oz
500 gm = 1 lb 2 oz
600 gm = 1 lb 5 oz
700 gm = 1 lb 9 oz
800 gm = 1 lb 12 oz
900 gm = 2 lb
1 kilo = 2 lb 3 oz

If you want an accurate conversion:

1 oz = 28.35 gm
4 oz = 113.4 gm
8 oz = 226.8 gm
12 oz = 340.2 gm
1 lb = 453.59237 gm
1 gm = 0.035 oz
100 gm = 3.527 oz
250 gm = 8.82 oz
500 gm = 1 lb 1.6 oz
1 kilo = 2 lb 3.27 oz

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