Carat and Karat Converter

NISAKE GAME

Contains ads

About this app

[PLEASE READ FIRST]
This app shows no prices and no market rates, and it cannot tell you whether
a piece is really gold. It takes a number and rewrites it in another unit.

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◈ Carat and Karat Converter — one word, two different things

For a gem, carat is a WEIGHT: 1 carat is exactly 0.2 grams.
For gold, karat is a PROPORTION counted in twenty-fourths: 18K is 18/24, 75 percent.

An 18 carat diamond is a 3.6 gram stone.
An 18 karat necklace is 75 percent gold.
The same 18, saying nothing alike.

English splits the spelling for exactly this reason, carat for the stone and
karat for the metal, though British English writes carat for both.
Japanese has a single word for the two. That is why this app keeps them on
two separate tabs: the split itself is the answer.

■ Gem and metal weight (six units)

Carat / point / g / mg / troy ounce (ozt) / momme.
Enter one number and the other five answer at once. Everything runs through grams,
and all six are defined values, so the figures do not shift from one reference to the next.

5 carats is exactly 1 gram; 1 gram is exactly 5 carats.
1 carat is 100 points. 1 momme is 18.75 carats, 3.75 grams.
1 troy ounce is 31.1034768 grams, 155.517384 carats.

■ Gold purity (three units)

K, counted in twenty-fourths / percent / per mille.
The whole calculation is K divided by 24.
18K is 75 percent, 24K is 100, 9K is 37.5.
There is no purity above 24 karat, and none above 100 percent.
Enter something outside that and the answers turn to a dash, with a line saying why.

■ Why exactly 0.2 grams

The trading nations agreed on it in 1907 and set it on the metric system,
which is why it is called the metric carat. Before that the figure differed from
country to country and market to market, and it is said to have started as the
weight of a carob seed. Seeds vary; a definition does not. That is why 5 carats
comes out at exactly 1 gram.

■ The karats that divide, and the ones that do not

Counted in twenty-fourths, whether the figure comes out clean depends on the numerator.
18K is exactly 75 percent, 12K exactly 50, 9K exactly 37.5.
But 22K is 91.66666667 percent and 14K is 58.33333333, and those never settle.
Part of why 18K is the best known is the workable hardness; the other part is this.

■ The stamped number is not quite the calculated one

A note inside the app sets K/24 in parts per thousand beside the mark you usually see.
The 750 on an 18K piece is exact; 14K calculates to 583.3 but is stamped 585.
This app converts with K/24 alone and never uses the stamped numbers.

■ Momme travels the world under its Japanese name

It is the unit of the pearl trade: exactly 3.75 grams.
English has no translation and simply writes momme. Of all the old Japanese units,
this is about the only one still used in international trade.

■ A troy ounce is not the ounce in your kitchen

It is the unit for gold and silver, exactly 31.1034768 grams.
The everyday avoirdupois ounce is 28.349523125 grams, a different figure again.
Both are here, kept apart, so the two do not get mixed up.

■ A quick table and ten shortcut buttons

The buttons are 1 carat, 5 carats, 0.5 carat, 100 points, 1 momme, 1 troy ounce,
18K, 24K, 9K and 750 per mille.
There are seven short notes, four on weight and three on purity.

■ Good for

▪ Finding out what a 0.5 carat stone weighs in grams
▪ Checking what a jeweller's "30 points" comes to in carats
▪ Seeing how far apart 18K and 14K sit in percent
▪ Turning momme from the pearl trade into grams or carats
▪ Putting a weight given in troy ounces back into grams

■ Features

▪ No account, no sign-in. The calculation is done on your device, and the numbers you type are not sent anywhere
▪ One screen only. There is no settings page
▪ Japanese and English (follows the device language)
▪ Five recent entries, tap to bring one back
▪ A quick table and seven short notes
▪ A converter and nothing else

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NISAKE GAME

What’s new

• An ad now appears when the app starts
• A Copy button now sits beside the answer. It copies the whole line, units and all, not just the number