The jewelry trade, and many others, typically measure items in millimeters, grams, and carats. Jewelers toss these terms around as if everyone was completely comfortable with the metric system of measurements.
To help put these measurements into a context everyone understands, lets measure some common, everyday items using the metric system. These lengths and weights are only close approximations of actual weights or lengths, but close enough to allow you to visualize what a millimeter or a gram represents.
- copy paper measures 1/10 mm thick
- 10 piece copy paper measures 1 mm thick
- 1 inch measures 25 mm
- #2 lead pencil measures 7 mm diameter
- a dime measures 18 mm diameter
- USB plug measures 4.5 X 12 mm W x L
- dollar bill measure 65 X 150 mm W x L
- dollar bill weighs 1 gram
- dollar bill weighs 5 carats
- a nickle weighs 5 grams
If someone throws out the term "pennyweight" instead of gram, one pennyweight (abbreviated DWT) is about 1.5 grams. Grams are often used for weighing fabricated, or built jewelry, while pennyweight is commonly used for the weight of a cast piece.
There are five carats in one gram, and 100 points in one carat. A 25 point diamond is 1/4 carat.