There is a simple formula to calculate the resale value of old gold jewellery. You need to know three things for that:-
Weight of Gold, Purity of Gold and Rate of Gold. Take your gold to a gold testing or assaying lab & have it tested for purity. They will give you a test report with the accurate weight of the sample & its purity in percentage or karats.
There are two ways that you can calculate the value of gold with:-
Let's say the gold weighed at 20 grams with a purity of 18 Karats (75%) & the rate of gold is ₹ 3,000 per gram.
Using karat purity the value of gold is:-
Using percentage purity the value of gold is:-