Grams to Pennyweights Converter

What this converter does

It converts grams to pennyweights by dividing by exactly 1.55517384. This is the direction needed when a metric scale meets a trade that quotes in pennyweights — which is the usual situation for anyone selling scrap gold in North America, since the seller scale is metric and the buyer unit is not.

The formula

Divide grams by exactly 1.55517384. A 10 g ring is 6.43 dwt. 31.1 g is almost exactly 20 dwt, which is one troy ounce. The constant is a twentieth of the definitional troy ounce, so the conversion is exact until the display precision you choose.

Worked examples

1 g is 0.643 dwt. 5 g is 3.215 dwt. 10 g is 6.430 dwt. 31.1035 g is exactly 20 dwt. A 47.3 g scrap lot is 30.4 dwt. And a 100 g bar is 64.3 dwt, though bars at that size would more naturally be quoted in troy ounces — the pennyweight is a jewellery-scale unit and stops being convenient above a few hundred.

Comparing offers made in different units

This is the practical reason to convert. A buyer quoting per pennyweight and another quoting per gram cannot be compared as written, because the pennyweight number will always look larger — the unit is 1.555 times bigger. Divide the per-pennyweight price by 1.55517384 to get its per-gram equivalent, then compare. Doing this before any negotiation removes the single most common confusion in scrap transactions, and it takes one operation.

The question that matters more than the units

Whether the offer is on gross weight or fine content. A 10 g piece of 14-karat gold is 6.43 dwt of mass but contains only 14 parts in 24 of fine gold, which is 5.83 g or 3.75 dwt of actual metal. An offer quoted per pennyweight of gross weight and one quoted per pennyweight of fine gold are entirely different propositions, and the gap between them is far larger than any difference in the headline rate. Establish the basis first; the unit conversion is the easy part.

Karat and what it means for the arithmetic

Karat states parts of gold in twenty-four by mass: 24-karat is pure, 18-karat is 75 percent, 14-karat is 58.3 percent, 10-karat is 41.7 percent. Multiplying the converted mass by that proportion gives the fine content. Note that karat is a purity and not a mass, so it never enters the unit conversion itself — it is a separate multiplication applied afterwards, and keeping the two steps distinct is what makes the calculation checkable.

Weighing at home before selling

A jewellery scale resolving 0.01 g is more than adequate, since a hundredth of a gram is about 0.006 dwt. Weigh pieces separately if they differ in karat, because a mixed lot weighed together cannot have its fine content calculated without knowing the split. Remove stones and non-gold components where possible, since a buyer will not pay metal prices for them and their mass otherwise inflates the gross figure in a way that only helps if the offer is on gross weight — which is precisely why the basis question comes first.

The rest of the troy chain

Divide the pennyweight result by 20 for troy ounces, or multiply by 24 for grains. Every step is exact, so the whole chain from grams to grains can be traversed in either direction without accumulating error. For anything above a few hundred pennyweights, troy ounces are the more readable unit and have their own pages in this cluster.

Common mistakes

Comparing raw price numbers across units. Ignoring fineness. Weighing a mixed-karat lot as one figure. Assuming the pennyweight is a form of the ordinary ounce — it is a troy unit and one twentieth of a troy ounce, which is about 0.055 avoirdupois ounces. And over-precision: a scale reading to 0.01 g supports two decimal places of a pennyweight, not four.

Benchmarks

1 g is 0.643 dwt. 2 g is 1.286 dwt. 5 g is 3.215 dwt. 10 g is 6.430 dwt. 15.552 g is 10 dwt. 31.103 g is 20 dwt, one troy ounce. 50 g is 32.150 dwt. 100 g is 64.301 dwt. The gram at 0.643 pennyweights, and its reciprocal at 1.555 grams per pennyweight, cover the arithmetic in both directions.

Accuracy and limits

Exact factor, exact decimal arithmetic, one rounding at the display precision you choose, and a parser that refuses ambiguous input with an explanation. The tool converts mass — not purity, not fine content, and not the value of a transaction whose terms it cannot see.

A worked valuation from end to end

Take a 12 g 14-karat ring. Convert: 12 divided by 1.55517384 gives 7.72 dwt of gross weight. Apply fineness: 14 parts in 24 is 58.3 percent, so the fine content is 4.50 dwt, or 7.00 g. Convert to troy ounces: 4.50 divided by 20 gives 0.225 oz t of fine gold. Multiply by the spot price for the metal value, then expect an offer below it reflecting refining. Every step is separately checkable, which is the point of doing it in stages rather than reaching for a single figure.

Stones, clasps and other non-gold mass

Anything in a piece that is not gold still registers on the scale. Stones, springs, clasps and base-metal cores all add gross weight without adding fine content, and a valuation on gross weight quietly pays for them at metal rates while a valuation on fine content does not. Where practical, remove or account for them before weighing — and where a stone is worth keeping, its removal is a separate decision from the metal transaction entirely.

Checking the conversion quickly

Grams times two thirds approximates pennyweights: 12 g gives about 8 against a true 7.72. The approximation runs a few percent high and is fine for confirming a magnitude before a more careful figure is needed. Its main use is catching the reversal error — multiplying by 1.555 instead of dividing — which produces a number nearly two and a half times too large and is immediately obvious against the rough check.

Keeping a record of the transaction

Write down the gross gram weight, the karat of each group, the converted pennyweight figure and the basis of the offer. Those four items reconstruct the whole valuation later, and any one of them missing makes a dispute unresolvable. The gram figure in particular is the measurement; everything else is derived from it, and a record holding only the converted pennyweight number cannot be re-derived if a rounding is questioned afterwards.