Adapted from Cleave Books Specialist Calculators Online (SCOL); by permission.
Conversion Calculator for Units of
Tons, Hundredweight, Quarters & Pounds
(Abbreviated as   tons, cwt, qtrs & lbs,   respectively)
Show values to . . . significant figures.

tons  &  cwt  &  qtrs  &  lbs
long (US) or Imperial (UK) tons
short tons (US)
pounds [lb]
kilograms [kg]
metric tons (tonnes)

combined (cwt-qtr-lbs):
On the Tons & Cwt & Qtrs & Lbs (first) line, the first three values must be whole numbers or blank;
also, Cwt must be less than 20 unless Tons is blank, Qtrs must be less than 4 and Lbs must be less than 28.
(Tons with decimals can be entered on the second line.)

The maximum input value is larger than any known bell.
Depending on your Web browser (or your Javascript implementation), output values with more than 3 digits to left or right of the (implied) decimal point may have those digits grouped in threes with spaces (European convention), not commas (American convention).

Unvalued zeros on all numbers (leading or trailing) have been suppressed.

NO guarantee as to the accuracy of these values is given.
For critical use, they should be checked against some other source.

Additional Information
Only in the Imperial system of measures are mixed units "allowed".  That is, measurements like
5 hundredweight 2 quarters 16 pounds
2 tons 15 hundredweight 3 stone
Note that the singular and plural forms of "hundredweight" are the same; this also holds true for the abbreviation "cwt" and for "stone".

In the SI or metric system, mixed measures are "not allowed", and they are certainly not necessary.  Something like
15 metres 78 centimetres 3 millimetres
is expressed as
15.783 metres

However, in spite of the valid arguments for use of the metric system, there also exist valid arguments for continued use of portions of the Imperial system in certain contexts.  One of those contexts is the ancient English tradition of change-ringing, using large bells hung in a particular manner in church towers.  (Though there are some other types of towers which hold such bells, and a different style of ringing changes can be done on handbells, it is the tower bells which are relevant to the present point.)  Thousands of towers, and tens of thousands of bells and ringers, are involved in The Exercise, not only in England but also in the rest of the British Isles and in North America, Australia, New Zealand and South Africa.  Hundreds of years of records regarding not only these bells but also various performances upon them are based upon a customary subset of the British Imperial system of weights.

The Imperial weight definitions are as follows:
16 ounces = 1 pound [lb]
14 pounds = 1 stone
28 pounds = 2 stone = 1 quarter [qtr]
112 pounds = 4 quarters = 1 hundredweight [cwt]
2240 pounds = 20 hundredweight = 1 ton
In change-ringing parlance, ounces and stones are not used at all; hence their absence from this calculator.  Also, tons are used only for approximate weights of huge bells; cwt is the basic unit for exact weights, as well as for approximate weights of ordinary bells.
Now consider the measurement of
6777 pounds
That could be stated by a ringer (or in ringing records) as
3 tons
61 cwt
60 1/2 cwt
The first figure is an approximation to the nearest ton, the second figure is an approximation to the nearest hundredweight, and the the fourth figure is an exact statement.  Note that in the last case the units are not stated and the three values are separated by hyphens.  By convention, all exact weights of 1 cwt or more are written thus, even if the second and/or third values are zero.  (In tables of information, spaces may be used instead of hyphens.)
This convention has the disadvantage that in some contexts it is unclear whether a weight is exact or approximate.  For example, 35-0-0 is probably approximate, but 22-2-0 could be either exact or approximate.

This calculator was adapted from the similar "Pounds and Ounces" calculator to serve the needs of the change-ringing community by bridging the gap between the traditional system of bell weights and the metric system of weights which is increasingly being used for all other purposes.

Go to the  Dictionary of Units   OR the  Calculator Menu
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Original ©FT2004,
Version 1.4;
This calculator adapted by CSZ, Dec.2003 and May 2004.
Now resident on the TowerBells Website.