What a troy pound is
The troy pound is the largest unit of the troy system, the family of weights that also contains the grain, the pennyweight and the troy ounce. It is a fixed definition, not a measurement: NIST Handbook 44 (2026), Appendix C, gives 12 ounces troy = 1 pound troy = 240 pennyweights = 5,760 grains.
Because the grain is defined exactly, as 64.798 91 milligrams, the troy pound comes to an exact figure in grams. 5,760 × 64.798 91 mg = 373.241 721 6 g. Twelve troy ounces of 31.103 476 8 g give the same number, which is how this converter checks itself: every unit on the page is derived from the one pound of 0.453 592 37 kg and from the grain, so no two figures can contradict each other.
Why a troy pound is lighter than an ordinary pound
The pound most people know, on a bathroom scale or a supermarket label, is the avoirdupois pound: 7,000 grains, 453.592 37 g. The troy pound is 5,760 grains, so it is about 18% lighter, 82.3% of an avoirdupois pound.
The ounces go the other way. A troy ounce is 480 grains and an avoirdupois ounce is 437.5, so the troy ounce is about 9.7% heavier. The reason is the number of ounces in each pound: twelve in the troy pound, sixteen in the avoirdupois. A heavier ounce, fewer of them, a lighter pound.
This catches people out with old inventories and antique silver, where a weight written as "lb" may mean either. A 2 lb figure means 746.5 g if it is troy and 907.2 g if it is avoirdupois, a difference of more than 160 g. Where the record does not say which, the honest answer is that the weight is ambiguous until the piece is weighed again.
The apothecaries’ units
The apothecaries’ system, once used to dispense medicines, shares the grain and the ounce with troy weight and divides the ounce differently. NIST Handbook 44 gives 20 grains = 1 scruple, 60 grains = 1 dram apothecaries and 480 grains = 1 ounce apothecaries. The UK Weights and Measures Act 1985, Schedule 1 Part VI, gives the same chain: ounce apothecaries = 480 grains, drachm = 1/8 ounce apothecaries, scruple = 1/3 drachm.
So an apothecaries’ ounce weighs exactly the same as a troy ounce, 31.103 476 8 g, and an apothecaries’ dram is 3.887 934 6 g. That dram is not the avoirdupois dram, which is 1/16 of an avoirdupois ounce, about 1.77 g. The two share a name and nothing else.
Where the troy pound is still used, and where it is not
Precious metals are priced per troy ounce, and the troy pound rarely appears in trade today. It turns up mainly in history: older assay records, coinage law and descriptions of silver plate. The British pre-decimal silver coinage, for example, was struck at 66 shillings to the troy pound of sterling, which the silver coin calculator on this site uses.
The UK Weights and Measures Act 1985 lists the ounce troy in Part V of Schedule 1, the part for units in use for trade, and lists no troy pound at all. The pound in that Act is the avoirdupois pound, and it sits in Part VI, among units that "may not be used for trade except as supplementary indications". The troy pound on this page therefore rests on NIST Handbook 44, and the page says so rather than implying a UK legal definition that does not exist.
Worked examples
Half a troy pound is 6 troy ounces, 120 pennyweights, 2,880 grains or 186.62 g. A silver tray recorded at 3 troy pounds 4 troy ounces is 40 troy ounces, 1,244.14 g. A kilogram is 2.679 troy pounds, or 32.15 troy ounces.
These are weights of the whole object. A sterling tray of 40 troy ounces contains 925 parts per thousand silver, 37 troy ounces of fine silver, and the rest is copper. The silver value calculator applies the purity and the live price to a weight; this page only converts the weight.