Ounces to carats:
multiply by 141.7476

How many carats are in an ounce?

One ounce is 141.7476156 carats. The ounce here is the standard avoirdupois ounce of 28.349523125 grams, and one metric carat is exactly 0.2 grams. Dividing the first by the second gives the 141.7476156 factor.

That makes an ounce a very large weight in gem terms. Even a modest bag of rough stones weighing a few ounces can run to hundreds of carats.

The ounce to carat formula

Going the other way, a 5 carat stone weighs 5 × 0.00705479239 = 0.03527 oz, a little over a thirtieth of an ounce.

1. 1Write the weight in ounces as a decimal.
2. 2Multiply by 141.7476156.
3. 3Round to two decimals, which is how gem weights are usually quoted.
4. 4Sanity check: one ounce should land a little over 140 carats.

Chart: ounces to carats

The values below use the exact factor and match the converter.

As a rule of thumb, one quarter of an ounce is about 35.4 carats and half an ounce is about 70.9 carats.

Working with gem parcels in ounces and carats

Rough gemstones, pearls and beads are often traded in bulk by weight, and a parcel might be described in ounces by a seller in one country and in carats by a buyer in another. Converting lets you compare per-carat prices. A 2.5 oz parcel at a total price of 900 is quoted per carat by dividing by 2.5 × 141.7476 = 354.37 ct.

Precious metals use a different ounce. The troy ounce is 31.1034768 grams, about 155.5 carats, so never apply the factor on this page to a quantity of gold or silver that is quoted in troy ounces.

A helpful check is to go through grams. An ounce is about 28.35 g, and each gram is five carats, so 28.35 × 5 = 141.75 carats, matching the factor. If your result for one ounce is far from 141.75, something went wrong in the multiplication.

Customs paperwork and shipping manifests sometimes list gemstones by ounce while the invoice uses carats. Converting a 0.4 oz shipment gives about 56.7 carats. Keep the full factor in your calculator and round only the final figure, because rounding the factor early compounds across large parcels.

For a rough mental estimate, multiply ounces by 140 and add one percent. Two ounces gives 280 plus 2.8, about 283 carats, which agrees with the exact figure of 283.5. This is quick enough to use while talking to a supplier, leaving the converter for the final invoice.

Common mistakes when converting ounces to carats

• Using the troy ounce factor for avoirdupois ounces, or the reverse. The two differ by about 10 percent.
• Mixing up carat and karat. Carats weigh gems, karats measure gold purity.
• Dividing instead of multiplying. A carat is much smaller than an ounce, so the carat figure must be larger.
• Rounding the factor to 140. That gives a 1.2 percent error, which is about 2.5 ct on a 200 ct parcel.