Dictionary of Units
Frequently Asked Questions
and Other Measures

Calculator Inputs & Browsers
A Shortcut
bels & decibels [dB]
BTU or Btu
cookery measures
fluid ounces
hoppus foot
lb & oz
miner's inch
rod, pole, perch

Calculator Inputs & Browsers
The input values (where it says 'Type in size . . .') for the calculators associated with the Dictionary of Units are expected to consist only of the characters
1 2 3 4 5 6 7 8 9 0
with not more than ONE decimal point and any amount of spaces. NO letters, NO commas. Almost anything else will get the message
'The input size was NOT a valid number'
Only the temperature calculator will accept a leading negative.

The language driving the calculators is JavaScript 1.2 which might cause difficulties for some browsers, especially if it has been disabled! Development and testing was done on Netscape 4.5 and 4.7 (7.0 seems to be OK as well)
Internet Explorer 5.0 seems to work on most of them but 5.5 is better. Don't ask!
Earlier versions will, and other browsers can, also throw up error messages.
So, please check your browser and its version before claiming that calculators are not working. Also make sure you are using the latest version of the calculator and that it came from this site. And check that JavaScript is ENABLED in your browser!
The task of making these calculators, and the Dictionary, 'fit' all browsers has not even been attempted, but they have been looked extensively on those mentioned above. However, even on those, the display settings on the user's own computer (as well as the exact browser version) can change the looks of things. So, if the the display looks "uneven" or "untidy", it is unlikely you are seeing it the way the author did!

A Shortcut
The menu for all the calculators used to change units is a part of the Dictionary of Units which requires a dowload of over 70k. That can be avoided by going directly to another menu (only 8k) at
Regular users might find it useful to call it now (from here) and bookmark it.

The barn is a very small unit of area used to express the cross-sectional area of the nucleus of an atom. It was defined in 1942 by Holloway and Baker (in Chicago) and the name was taken from the expression "as big as a barn door" which it was, relatively speaking, in their particular work with sub-atomic particles.
1 barn = 10-28 square metres
Later, following on from that idea, the 'shed' an even smaller unit was defined, but this seems never to have been taken up by the scientific community.
1 shed = 10-24 barns = 10-52 square metres

The word 'barrel' is both a name for a type of container and also a unit of measure. As a container, the once very familiar barrel was made of wood and roughly cylindrical in shape except that it 'bulged' outwards in the middle, and was used to transport not only the obvious liquids (water, beer, wine etc.) but also other commodities such as fish, sugar, flour, meat, cement, minerals, and so on. The sizes of the different barrels varied with contents and, some of these different barrels acquired different names. So, deeper enquiry must be made if the exact quantity meant in any particular context is wanted. The sizes given here are to help the modern reader who wishes only to have a rough idea of just how big something might have been.
Small numbers like 123 are the equivalent size to the nearest litre.
For liquids similar to water (wine etc) this is also the weight of the contents in kilograms.
barrel = 36 galls(UK) 164
butt = 108 galls(UK) 491
firkin = 9 galls(UK) 41
hogshead = 54 galls(UK) 245
kilderkin = 18 galls(UK) 82
pipe = 126 galls(US) 477
pin = 4.5 galls(UK) 20
puncheon = 70 galls(UK) 318
tierce = 42 galls(US) 159
tun = 216 galls(UK) 982
A study of the sizes shows the relationships between some of these containers.
Like: 1 tun = 2 butts = 4 hogsheads = 6 barrels = 12 kilderkins etc.
The use of the US gallon betrays the origins of the container as being in the wine trade. It was the old UK wine gallon which later became the standard US liquid gallon.
The unit of a barrel as used in the oil trade is, in fact, the tierce which is one-third of a pipe. 'Tierce' and 'pipe' were used for both containers and measures in the wine trade.
Some other names for barrel-like containers of unspecified size are
breaker    cask    drum    keg    tub

bels & decibels
Abbreviations are B and dB respectively.
The bel was originally a measure of sound intensity based on a logarithmic (base 10) scale. This means that each increase of 1 bel is 10 times louder than the one before it. The need for such a scale is that the measurement of noise covers such a big range. A really loud noise is billions of times louder than a quiet one. On this logarithmic scale, one billion is only 9.
1 billion = 109
It is named after Graham A. Bell (1847-1922) who invented the telephone.
However, it is the decibel (one-tenth of a bel) which is much better known and used. On this scale, a value of 0 dB represents the smallest amount of sound that can actually be detected, 50/60 dB would be the level of ordinary conversation, and above 130 dB of noise would cause pain.
The dB logarithmic scale idea has since been adopted by other specialist areas, most notably in electronics. Here they use it to measure power. Thus dBW for decibel watts, and dBmW for decibel milliwatts (in laser work) which, unhelpfully for us, they often write as dBm.
Some other (related) words are:     neper    phon    sone
For much more detailed information on all of this,
go to the A to Z of units listed at (and linked from) the

The bottle is a well-known container of all kinds of liquids. It is not a legally defined measure, though for certain purposes there is common agreement on what size it should be. However there are different ways in which the capacities of bottles are stated. For instance, milk bottles give it in litres, wine bottles in centilitres [cL] and smaller sizes of soft-drink bottles in millilitres [mL]. Of course there are marketing ploys at work here ~ 330mL sounds more than 33cL and certainly much more than 0.33L !
How did the wine bottle come to be 75 cL in size? It has a long and complicated history but, briefly, in the 1600's when bottles were made by hand, the wine bottle was about 46.24 cubic inches (26 and two-thirds fluid ounces) in capacity, a measure which was known as a 'reputed quart'. This came from being one-quarter of a wine gallon which was the size of 8 troy pounds of wine. (Wine by the pound!) Metrication trimmed one and a half teaspoonsful off this to make it 75cL.
One set of bottle sizes which always fascinate is that used for champagne. The names, with their generally accepted measures, are
bottle= 1 bottle= 75 cL
magnum= 2 bottles= 1.5 L
jeroboam= 4 bottles= 3 L
rehoboam= 6 bottles= 4.5 L
methuselah= 8 bottles= 6 L
salmanazar= 12 bottles= 9 L
balthazar= 16 bottles= 12 L
nebuchadnezzar= 20 bottles= 15 L
The large sizes are rarely used, except for very special
(and expensive) occasions when they are usually made to order.
Some other names of bottle-like containers are
amphora    ampoule    ampulla    blackjack    calabash    chagal
demijohn    flagon    flask    gallipot    gourd    phial    vial

A measure of the percentage of sucrose contained (by weight) in a sugar solution at a temperature of 17.5°C. It is measured by using a saccharometer (=hydrometer) graduated in degrees of Brix, where 1 degree = 1%
It is important to know this value during the fermentation process of alcoholic drinks (wines & beers) since the alcoholic content of the final liquid is determined by the amount of sugar present at a certain stage.
The measure was devised by A F W Brix (1798-1870) a German chemist.
BTU or Btu
Both are measures of energy. The BTU is the Board of Trade Unit and is equivalent to 1 kilowatt hour (kWh) but is no longer used. The Btu, or BThU, is the British Thermal Unit (equivalent to over 3000 BTU's) which is obsolete but still seen quite a bit. The SI unit of energy is the joule.
This was a measure of length used at sea. In the UK it was defined as 100 fathoms (600 feet); and in the US as 120 fathoms (720 feet). Informally, it was also regarded as one-tenth of a nautical mile (608 feet) in the UK. The unit is no longer used operationally, and neither is the fathom.
The level of cholesterol in one's blood is an important measure of the state of one's health, especially in terms of assessing life expectancy. Unfortunately, 2 different ways of measuring it are used.
In the US it is given in mg/dL (milligrams per decilitre or 100 millilitres) while the UK uses mmol/L (millimoles per litre). To change from one system to the other:
From US to UK units divide by 38.6
from UK to US units multiply by 38.6
As a rough guide to the sort of figures expected: in UK units it should be less than 5, while in US units the total should be less than 200.
Then there is the matter of good and bad cholesterol. But that has nothing to do with the units used to measure it.
cookery measures
What a mess! The system of measures that is. It must be realised that the measures used had their origins in the days when the ordinary kitchen had no specific measuring utensils (scales or graduated jugs) and recipes had to give the required amounts in terms of what would be to hand, like 'teaspoons' 'tablespoons' and 'cups'. Given that the sizes of such things did not vary very much in those times, and that recipes are basically only about proportions between ingredients, it all worked very well.
A look now in almost any kitchen will show just how much these things can vary in size, and indicate that some sort of 'standardisation' is needed. The simple answer is to give weights and volumes in regular measures (metric preferred) and avoid any reference to utensil measures. Or, alternatively, specify what size those measures are intended to be. This latter is much better since many of the smaller quantities would be quite difficult to measure. Most cookery books nowadays usually include a section giving guidance on this topic.
Of course, that still leaves the problem of working from an old recipe.
As a guide, and nothing more than a guide, try
1 teaspoon = 5 mL
1 tablespoon = 15 mL = 3 teaspoons
1 cup = 250 mL (= one-quarter of a litre)
Of course, if it is a dry ingredient, then it is necessary to know whether the spoon is to be 'heaped' or 'level'
And then there are   'pinch'   'handful'   &   'teacup'.
Never mind, think of cooking as an art, and not a science.

This measure is much used in medicine for prescribing dosages for treating ailments of the nose, ear and throat. Surprisingly, the exact size of a drop is NOT defined, but everyone 'knows' roughly what it means, though variations can be found in the literature.
In general, it can be taken that
1 drop = 0.05 millilitres (mL)
which means 100 drops would fill a 5 mL teaspoon.

This symbol is now often seen on packaging which originates from within the European Union. It is NOT a unit of measurement.
It is a lower case 'e' which is printed adjacent to (before or after) the stated (nominal) quantity of the contents of the package. Thus
e 150g   or   275mL e
It indicates that the quantity stated lies within the limits allowed by the rules given under
The Average System of Weights and Measures

This stands for "electronvolt" and is a measure of energy used in nuclear and atomic physics. It is a very small unit and is more usually seen as keV, MeV or GeV (that is kilo- mega- and giga- eV).
1 eV = 1.602 176 462 × 10-19 joules
But, since this figure has to be determined by experiment, its value might be a little different in other printed sources (depending on date of publication).
fluid ounce
This is a measure of volume and not mass or weight. This is because it is defined in relation to the gallon.
In the UK 160 fl.oz. = 1 gallon
In the US 128 fl.oz. = 1 gallon
This looks like a big difference but, the UK and US gallons are not the same size. Changing to a common unit we have
In the UK 1 fl.oz. = 28.413 063 mL
In the US 1 fl.oz. = 29.573 530 mL
(A difference of about 4%)
The original intention (in both cases) had been to make the fluid ounce also equal to one ounce of water in weight. In fact
In the UK 1 fl.oz. = 1.002 241 oz
In the US 1 fl.oz. = 1.043 176 oz
Considering their closeness and that they are only (usually) used for non-scientific measurements it is not unreasonable to treat them as being the same size and weighing 1 ounce.
But, if really pressed, there are (small) differences!

also gage or gages
This is one of the more overworked words in the English language. Major dictionaries identify over 15 different usages of this word!
First of all, for the use we make of it in connection with measuring, it is NOT a unit in itself. It can best be thought of as a collection of standard sizes. Each collection having its own identity and not necessarily having any relationships within itself or with any other collection.
A characteristic of nearly all collections of gauge sizes is that the size is given by a number and you need to refer to a table in order to find exactly what size or dimension that number stands for. Neither do you know beforehand whether bigger numbers mean bigger (or smaller) sizes.
The standard sizes used for a collection are most often laid down by the ruling, or organising, body concerned with the use of whatever it is that is being measured. It is most unusual for any gauge sizes to defined by government legislation. (Unlike, for instance, our measures of weight, length etc.)
One of the better known examples of gauge sizes is that used for wire where there are such well-known names as American (or Brown & Sharpe); Birmingham (or Stubbs); British Imperial (or S W G);
Gauge sizes are also used for sheet-metal, model railways, knitting and sewing needles, shot-guns, and several other things.
Though not usually referred to as gauge sizes, though in principle they are, we have those for clothes and shoe sizes, and the Beaufort wind scale.

This is a measure of length which, if nothing else, serves to remind us how many length-units had their origin as a part of the human body which served as a convenient built-in measure to be used to size up something with a rough and ready degree of accuracy. For general use it has long been obsolete, but it is still used to measure and record the height of a horse.
1 hand = 4 inches (just over 10 centimetres)

hoppus foot
This is a measure of volume once used in forestry work but now obsolete. It was derived from a formula used to find the volume of usable wood in the trunk of a tree, after an allowance had been made for waste (about 20%).
1 Hoppus foot = 0.036 cubic metres
The unit was named after Edward Hoppus, an English surveyor, who devised the system in 1736.

Also spelt klik or click.
It is principally a measure of length or distance, and is equal to 1 kilometre
There seems to be some doubt about when it first originated, but certainly was in wide use by the US military in the Vietnam War (1961 - 75).
It is also sometimes used to mean a speed of 1 kilometre per hour.
lb & oz
These are very well-known abbreviations for the pound and the ounce, but where did they come from?
When the Romans came to Britain they brought their own system of measures. For weighing they used the 'libra' and 'uncia' (which was one-twelfth of a libra). When the English language was forming the word 'pund' appeared and was concerned with weighing, but slowly changed (to pound) to mean the weight itself, which was the libra, and the abbreviation 'lb' was retained.
It is not hard to see how 'uncia' became 'ounce' but why 'oz'? Hazy! The 'best' story is that the merchants of those times were always looking for contractions for frequently written words and for ounce wrote o+squiggle which got formalised over time into oz. (An example of early text-messaging?)
But what about its size? There are not 12 ounces in a pound. Well not now. The original pound was the Troy pound which did have 12 ounces. Later the standardised pound Avoirdupois (7000 grains) was introduced, this was bigger than the Troy (5760 grains). But they decided to have 16 ounces in the pound which made the new ounce (437.5) smaller than the old one (480).
Note that the 'uncia' as the one-twelfth part of a measure was retained in English measures as a division of the 'foot' but in that case its name evolved into 'inch'.
Inevitably, liberties have been taken in re-telling 2000 years of history in so few words!
In reality it was an evolutionary and very uneven process.
Going 'metric' is a doddle in comparison!

These are the same measure. The difference is only in the spelling. In UK English it is 'litre', in US English it is 'liter'.
There can be some ambiguity about the size of the litre. When the metric system was introduced in the 1790's the litre was intended to match up with the volume occupied by 1 kilogram of pure water at a specified pressure and temperature. As the ability to measure things got better (by 100 years later) they found that there was a mismatch between the kilogram and the litre. As a result of this they had to redefine the litre (in 1901) as being 1.000028 cubic decimetres. Very handy!
This nonsense was stopped in 1964 when it was ruled that the word "litre" may be employed as a special name for the cubic decimetre, with the additional recommendation that, to avoid any possible confusion,
'in high-accuracy work the name "litre" should not be used.'
So now the litre is taken as being a cubic decimetre, or
1 litre = 1000 cubic centimetres (= 1000 mL)
It should be remembered that one unusual feature of the litre is its abbreviation. It is unique in that two forms are allowed. In 1979 the governing body who control the SI ruled that the letter used as the abbreviation for litre could be written in either lower or upper case, 'l' or 'L', to avoid possible confusion with '1'(one). They hoped one day to make a decision on one or the other, but have not done so yet. It seems a pity that the 'L' appears to be so little used. It is clearer on printed material (mL rather than ml) and certainly much the better way for written matter. Given the number of cases that come to notice from time to time in medical work where a wrong dosage has been administered, perhaps it should be made mandatory in that field at least.
Stands for "microgram" or one-millionth of a gram. It is not an 'officially' approved abbreviation. It should be written µg
However, the difficulties of printing the Greek letter "µ" led to the use of "mcg". Nowadays there is rarely a real need for this; it is largely a matter of laziness.
These are the same measure. The difference is only in the spelling. In UK English it is 'metre', in US English it is 'meter'.
No matter how it is spelt, it is the standard by which all other measures of length are defined. For example a 'foot' is 0.3048 of a metre and so on.
One advantage of the UK form is that it allows a clear distinction to be made between the 'micrometre' which is one-millionth of a metre and a 'micrometer' which is an instrument used (mainly by engineers) to measure small sizes with great accuracy.
symbol µ (the Greek letter mu)
"Micro" means one-millionth and the word micron means one-millionth of a metre. It is often used as a measure of thickness for sheet metal and card.
It is still in very common usage though no longer an approved SI unit.
It should be "micrometre" or µm.

miner's inch
This is NOT a measure of length, but of the rate of water flow in a miner's sluice. A sluice is used in getting metallic ores (like gold) from the gravel containing them by a system of washing in which the rate of flow of the water is very important. Too fast and it takes away everthing, too slow and nothing happens.
1 miner's inch is a flow of 1.5 cubic feet per minute or about 64,000 litres in 24 hours.
As a measure this is now obsolete. It was once used as a measure of length for cloth, and was equal to one-sixteenth of a yard (two and a quarter inches). It was also a measure of weight for wool or beef and equivalent to 8 pounds. Its alternative name was a 'clove'.
Where the 'nail' is a type of fastener (for wood) it picked up another measure in US usage. The size of the nail was expressed by the cost (in pennies) of 100 nails of that size. Thus a one-inch nail would have been two-penny nail, while a four-inch nail would have been a twenty-penny nail and so on.
rod, pole or perch
These have meant different things at different times and in different countries! But most commonly they may be taken to be alternative names for the same unit of length, and equal to 5 yards or 16.5 feet. Sometimes the 'rod' being referred to is meant to be a unit of area, and it will be necessary to read the context carefully to see if this is so. In that case it is equal to 272.25 square feet.
They are now obsolete, but do seem to come up quite often.
For more detailed information on these measures, look under 'rod' in
the A to Z of units listed at (and linked from) the

This common household implement has long been used as a measure of dosage when dispensing medicine at home. So what size was it? Well it varied, there was no standard until about the middle of the last century when it was set (by general agreement) at 5 millilitres (5mL) and, to make sure, free plastic "teaspoons" were given away with the appropriate medicine.
This is fine with liquids but what about a medicine which is in the form of granules or powder? Should it be a level measure or a heaped one? The latter can be twice the size of the former! One manufacturer (of supplements) when challenged on the amount of the various ingredients in a dose argued that a heaped teaspoon was needed, but it did not say so on the package. So, ask!
And then there is the teaspoon used in cookery . . .
Meanwhile the US National Institute of Standards and Technology give a teaspoon as 4.928 922 mL (An example of spurious accuracy that is hard to beat!)
This is a Russian measure of length (now obsolete) equal to a little more than a kilometre (1.067 km) or about two-thirds of a mile.
A very extensive A to Z of units by Russ Rowlett
is available from his site at the University of North Carolina.

Go to The Dictionary of Units