Gold jewellery price calculation: Gold jewellery is available in different purities, including 22KT, 18KT and the increasingly popular 9KT, with higher karatage indicating greater gold content. The gold value is calculated by multiplying the net weight by the applicable per-gram rate for its purity. However, know that diamonds are priced separately. Their value depends on the 4Cs: carat weight, cut, colour and clarity.