Units of Measure index

Imperial Measures of Weight


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This page gives Imperial units of weight. There is a quick convertor below which gives an answer rounded to 2 decimal places. The metric equivalents on this page are also all to 2 decimal places. There are more advanced conversions on the tables page.

Enter value:   =   ?  

Well-known units (avoirdupois) - ounce (oz), pound (lb), stone
Large units (avoirdupois) - quarter, hundredweight (cwt), ton
Small units (avoirdupois) - dram, grain
Troy weights - pennyweight, troy ounce, troy pound
Apothecaries' weights - scruple, apothecaries' drachm, apothecaries' ounce, apothecaries' pound
Jewel weights - carat, point
Mass v. weight
Which is heavier, a pound of lead or a pound of feathers?


Well-known units - Everyone knew these and used them constantly. These weights are avoirdupois (which comes from Old French "to have weight"). These were described like that in the tables that we had to learn. Other weight systems include troy weights and apothecaries' weights.
conversion
Abbrev.MetricTableInformation
ounceoz28.35 gram16 oz = 1 lb Ounce weight '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. The apothecaries ounce and troy ounce are now different weights.
The abbreviation "oz" comes from 15th century Italian, 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 British tend to weigh cooking ingredients rather than use cups (a volume measure). Old fashioned scales had metal weights which were balanced against what you were weighing (see right and below).
poundlb453.59 gram16 oz = 1 lb
14 lb = 1 stone
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. Winnie the Pooh wrote a poem about Tigger: Weighing scales
          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". Pooh sensed that the rhythm required an extra (poetic) foot.
The American pound cake was originally so-called, because it used a pound each of its main ingredients, flour, sugar, butter, eggs. It is sometimes baked in a tin with a hole in the middle, called a Bundt pan, or a loaf tin, or a round tin. The Victorians in Britain also baked pound cakes, but added a pound of dried fruits, such as raisins. Now no-one in Britain makes pound cakes but Victoria sponges are common, both as cakes and puddings such as Eve's Pudding. The ingredients are 4oz (quarter pound) of self-raising flour, sugar, butter and 2 eggs. The eggs also weigh 4oz, so the raw ingredients weigh a pound in total.
There is a troy pound which is a different weight.
stonelb6.35 kg14 lb = 1 stone The British weigh themselves in stone and the Americans weigh themselves in pounds. There are more advanced conversions on the tables page, but here is a simple conversion table.
Stone1234567891011121314151617181920
Pounds (lb)14284256708498112126140154168182196210224238252266280
Official standard weight The stone was originally used for weighing agricultural commodities. Historically the number of pounds in a stone varied by commodity, and was not the same in all times and places even for one commodity.
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. This is a standard weight from Manchester both dated 1754 and made of cast brass. It is now in the Museum of Science and Industry in Manchester.
The plural of stone is also stone. I weigh 10 stone, not 10 stones.

Rough conversion between Imperial and Metric

Britain is supposed to use metric measures. Volumes are not so much of a problem, as we buy bottles or packs of this or that, and we have been allowed to keep our pints of beer! But we can buy meat, and fruit and vegetables, by weight, and so we really ought to learn how to do this. Formal conversions are too precise, so here is a rough-and-ready guide that you might be able to keep in your head.

A bag of sugar weighs a kilogram, often called a kilo. This is slightly heavier than the old days, when it weighed 2 lb.
If you're buying fruit and veg, then (roughly) 1 lb is half a kilo.
8 oz is between 200 grams and 250 grams. A pack of butter is now 250 grams, but some other goods choose 200 grams instead.
4 oz is more than 100 grams.
A Smartie weighs about a gram.
Here is a mnemonic: "Two and a quarter pounds of jam weigh about a kilogram." (or of course anything else!)

Below are rough conversion charts. Work out what weight of meat or fruit or vegetables you normally buy, and memorise the metric equivalent.

1 oz = 30 gram
2 oz = 60 gram
4 oz = 110 gram
8 oz = 230 gram
12 oz = 340 gram
1 lb = 450 gram
1 lb 4 oz = 570 gram
1 lb 8 oz = 680 gram
1 lb 12 oz = 800 gram
2 lb = 900 gram
100 gram = 3.5 oz
200 gram = 7 oz
300 gram = 10.5 oz
400 gram = 14 oz
500 gram = 1 lb 2 oz
600 gram = 1 lb 5 oz
700 gram = 1 lb 9 oz
800 gram = 1 lb 12 oz
900 gram = 2 lb
   1 kilo = 2 lb 3 oz




Large units
conversion
Abbrev.MetricTableInformation
quarterqtr12.7 kg2 stone = 1 quarter
4 quarters = 1 hundredweight
This is a quarter of a hundredweight, not be to confused with a quart, which is a quarter of a gallon. There is also a volume unit called a quarter which was supposed to be a quarter of a chaldron and also a quarter of a yard.
A tod was the same weight as a quarter. It was used to measuring wool.
hundredweightcwt50.8 kg112 lb = 1 hundredweight
4 quarters = 1 hundredweight
20 hundreweight = 1 ton
The abbreviation 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.
Long hundredweight, quarters and pounds are used in this Philadelphian flour mill account book from 1747.
1.8 cubic feet of water weighs 1 hundredweight.
ton1016 kg2240 lb = 1 ton
20 hundreweight = 1 ton
This is the long ton or UK ton of 2240 lbs or 20 long hundredweight. The short ton is 2000 lbs or 20 short hundredweight. 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 216 gallons. Tons were in use in the late 15C.
Informally, we tended to use a ton when we meant something very heavy. "This suitcase weighs a ton!" Ton seems to have been sometimes spelt 'tonne' or 'tunne'. The 'tonne' spelling may now imply the metric unit.




Small avoirdupois units
conversion
MetricTableInformation
dram1.77 gram27.34 grains = 1 gram
16 drams = 1 oz
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. It was called this because it was (approximately) the weight of the Greek coin called the drachm. A Scots dram is a small glass, probably of whisky! But that is a volume rather than weight.
grain64.8 milligrams437.5 grains = 1 oz avoirdupois
7000 grains = 1 lb avoirdupois
The grain is a very small unit which is the basis of all three Imperial weight systems, the avoirdupois, the troy and the apothecaries. It was originally the weight of a grain of wheat.


Troy weights - These 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. The troy system dates from the 10C. The troy pound was defined as different from the avoirdupois pound in the reign of Elizabeth I. See a Tudor set of measures, where the table defines troy weights, and then separates avoirdupois and troy weights without giving the conversion factor!
conversion
MetricAvoirdupoisTableInformation
pennyweight1.56 gram0.055 oz24 grains = 1 pennyweight
20 pennyweight = 1 troy oz
A pennyweight was called that because it was the weight of a silver penny. I've been told that the abbreviation is DWT.
troy ounce31.1 gram1.1 oz480 grains = 1 troy ounce
20 pennyweight = 1 troy oz
12 troy ounces = 1 troy pound
The apothecaries' ounce was the same size as the troy ounce.
Statutory Instrument 1995 No. 1804 allows the use of the troy ounce for transactions in precious metals such as gold.
troy pound373.24 gram13.17 ounce
0.82 pound
5760 grains = 1 troy pound
12 troy ounces = 1 troy pound
The troy pound is no longer in legal use.
The apothecaries' pound was the same size as the troy pound.


Apothecaries' weights - These were used for measuring drugs and medicines. The grain was also part of this system.
conversion
MetricAvoirdupoisTableInformation
scruple1.3 gram0.046 oz20 grains = = 1 scruple
3 scruples = 1 apothecaries' drachm
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!
apothecaries' drachm3.89 gram0.14 oz60 grains = 1 apothecaries' drachm
3 scruples = 1 apothecaries' drachm
8 apothecaries' drachm = 1 apothecaries' oz
'Drachm' is short for 'dram'. The avoirdupois dram is smaller than the apothecaries' drachm. There is also a fluid drachm (a unit of volume) which is 1/8 of a fluid ounce.
apothecaries' ounce31.1 gram1.1 oz480 grains = 1 apothecaries' ounce
20 pennyweight = 1 apothecaries' oz
12 apothecaries' ounces = 1 apothecaries' pound
The apothecaries' ounce was the same size as the troy ounce.
apothecaries' pound373.24 gram13.17 ounce
0.82 pound
5760 grains = 1 apothecaries' pound
12 apothecaries' ounces = 1 apothecaries' pound
The apothecaries' pound was the same size as the troy pound.
Scales with apothecaries' weights This is a pair of scales with some apothecaries' weights. These are, left to right, ounce, half ounce, two drachms, two scruples and five grains. 'S' means a half (semi), '°' means one ('i') and 'ij' means two ('ii'). The ounces are marked with a funny 'Z', to mean 'oz', and they seem to be apothecaries' rather than avoirdupois. I suppose that '3' means drachm and the back-to-front Greek 'E' means scruple. I deduce that the 5 weight is grains, as nothing else is small enough.

Ounce apothecaries' weight Half ounce apothecaries' weight Two drachms apothecaries' weight Two scruples apothecaries' weight Five grains apothecaries' weight

This is a more conventional set of scales. I think it is a butcher's scales. You would weigh meat by putting on the flat slab on the left, and the weights on the right. The heavier side would go down, and you would change the weights until you get the right weight. The weights are laid out in front.

Weighing scales




Jewel weights - Troy weight was used for precious metals and stones. But individual stones may be described using carats.
conversion
MetricAvoirdupoisTableInformation
carat200 milligrams3.09 grains200 milligrams = 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', as a measure of purity rather than weight. 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 'karat' to distinguish it from the other 'carat'.
point2 milligrams0.03 grains2 milligrams = 1 point
100 points = 1 carat
A different type of point is a measure of the size of a font.




Mass v. weight

Mass and weight are not the same thing. Weight is a force, and varies throughout the universe. Mass remains the same. If you were on the Moon, your weight is less, because gravity is less. If you jumped, you would go higher. If you are in free-fall, for example in orbit, then you become weightless. People get confused as an object's mass (in pounds mass) and weight (in pounds weight) have the same numerical value (approximately) when you are on Earth.

In metric measurements, the unit of mass is the kilo and the unit of force is the newton. You would have thought that Imperial units (or U.S. Customary systems) would have sorted this problem out, but no! I was criticised, in my opinion rightly, by an 11 year old correspondent, who said that pound (lb) measures mass, not weight, and so my webpage ought to be titled Mass. The Imperial unit of weight is pound weight (or lb wt). I remember learning this distinction in my Physics class (in Britain) back in the 1960s. However, I defended myself as saying that these pages were really documenting history rather than science, as they were inspired by the tables on the back of my exercise books in the 1950s and 1960s, and these were always described as Weights and Measures (and had lb, not lb wt).

However, another correspondent said "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." There does seem to be a confusion here. Scienceworld.wolfram.com says "A pound is a unit of weight in the British engineering system equal to 4.448 newtons that is commonly used in the United States. Unfortunately, there is a great deal of confusion about the definition of the pound, with many authors using the unit to denote the mass-equivalent of 4.448 newtons, namely 453.592 grams. The use of the unqualified term 'pound' is therefore discouraged, with the more descriptive terms pound-mass (abbreviated lbm) and pound-force (lbf) being preferred. The confusion between pound-mass and pound-force alone is a good reason to use metric units wherever possible."

I suspect that there is a difference between British and American use. 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 as 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 1890s, and in the 1950s 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.' The slug, as I mentioned before, is simply a convenient unit to use so that it takes 1 lbf to accelerate it 1 ft/s2. " I must point out that Physics students in Britain did not use pound as a unit of force! Nowadays, they all use metric.

Mass can be measured with a balance scales (as long as there is any weight present at all) since this compares the object against known masses (called, unfortunately, weights!) A spring balance will measure weight, as this is what presses against the spring, and will push less under lighter gravity. Old fashioned scales are balance scales and modern scales are spring balances, so that doesn't help us, since they are both marked in pounds!

A poundal is the unit of force required to give acceleration of one foot/sec2 to a one pound mass. One pound weight gives acceleration of 32 feet/sec2 to a one pound mass on Earth, which is 32 poundals.

One last point: The newton is the metric unit of force. It is roughly the weight of an apple on Earth. Who says that scientists don't have a sense of humour!




Which is heavier, a pound of lead or a pound of feathers?

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, an ounce of gold or an 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 (which has no atmosphere, and so no air resistance) was to drop a feather and a piece of lead together. It looked strange to see them drop at the same speed!

Pound weights