Credit to mdfuk

Zero your scales and weigh the object you want to test, make a note of the weight. This ring weighed 3.91 grams.

Place a cup of water on a set of digital scales that are accurate to two or more decimal places. I’m using a Clear plastic cup as it’s the lightest one I have that is clear so you can see what’s going on, but something like a plastic cup from a coffee vending machine is lighter. Heavier glass cups will tip your scales over. Reset to Zero, on my scales this is the Tare button.

Tie the object to a piece of cotton of something similar, I’m actually using a bit of string that came off the netting that comes around oranges as it’s very light and non-absorbent. Suspended the object in the water, just below the surface so as little as possible of the string is added to the equation. Wait for the scales to settle and take the reading. In this case with the ring, it was 0.25 grams.

Simple Math

(Weight of the object) divided by (weight of water displaced)

In this case :- 3.91 / 0.25 = 15.64

Metal Density

Gold 19.3

Silver 10.5

Platinum 21.4

Palladium 12.0

Copper 9.0

9ct 10.9 to 12.7

14ct 12.9 to 14.6

18ct Yellow 15.2 to 15.9

18ct White 14.7 to 16.9

22ct 17.7 to 17.8

Sterling Silver 10.2 to 10.3

950 Platinum 20.1