Pennyweight Conversion Calculator

A unit that exists to confuse comparisons

A pennyweight is a twentieth of a troy ounce, 1.55517384 grams. It survives in the American jewellery trade because casting and scrap have long been priced per dwt, and the whole supply chain quotes in it.

That has a commercial consequence. A price per pennyweight is a smaller number than the same price per gram — a factor of 1.555 smaller — so a quote in dwt reads as cheaper than an equivalent quote in grams unless you convert.

It is also easy to confuse with the carat, which is a different unit for a different purpose: 1.555 g against 0.2 g. A pennyweight is nearly eight carats.

A worked example

A refiner quotes $60 per pennyweight for 14k scrap. Dividing by 1.555 gives $38.58 per gram. A competing quote of $40 per gram is the better offer, despite the larger-looking pennyweight figure being the one that catches the eye first.

On a 100 gram lot, that is $3,858 against $4,000 — $142 for a conversion nobody was hiding, but nobody was doing either.

Where the answer misleads

The conversion is exact, so the only risk is unit confusion. Where a quote does not state its unit, ask: dwt, gram and troy ounce prices for the same metal differ by factors that look like negotiating room.

Scales sold for jewellery often read in grams, pennyweights, carats and ounces, and switching modes accidentally is a common error. Check the display unit before recording a weight, particularly on a scale someone else last used.

Finally, a pennyweight price usually applies to a stated purity. A $60 per dwt quote for 14k is not the same offer as $60 per dwt for 18k, and comparing them without normalising for fineness compares nothing.