Free calculators for diamond and jewellery businesses
Seven quick calculators for the trading desk and the factory floor. They run in your browser and nothing you type is saved or sent anywhere.
Rapaport discount calculator
Net price per carat and stone total from the Rap list price and your discount.
How it is calculated
Net per carat = Rap list price × (1 + discount ÷ 100). A discount of −35% on US$7,200 gives US$4,680 per carat. Stone total = net per carat × carats, then converted at the day’s exchange rate.
Diamond mm to carat estimator
Estimate a diamond’s weight from its measurements.
How it is calculated
Round: average diameter² × depth × 0.0061. Fancy shapes: length × width × depth × a shape factor (oval 0.0062, princess 0.0083, cushion 0.0080, emerald and Asscher 0.0080, radiant 0.0081, pear 0.0059, marquise 0.0058, heart 0.0059). Girdle thickness changes the real weight, so treat this as an estimate.
Gold fine weight and value
Fine gold in grams and tola, and its value at your rate.
How it is calculated
Fine gold = gross weight × purity. 25 g of 22K (91.6%) is 22.9 g fine. 1 tola = 11.6638 g. Value = fine grams × the 24K rate per gram.
Jewellery price with making charges
A full quote: metal, making, diamonds, other stones and tax.
How it is calculated
Metal = weight × purity × the 24K rate. Making = weight × making charge per gram. Diamonds = carats × price per carat. Quote = (metal + making + diamonds + other) × (1 + tax ÷ 100).
Tunch and melting loss
Fine metal lost between issue and receipt, for a karigar or a melt.
How it is calculated
Each side is turned into fine metal (weight × purity), then subtracted. Loss % = fine loss ÷ fine issued × 100.
Kapan yield and profit
Yield, cost per polished carat and margin for a rough lot.
How it is calculated
Yield % = polished carats ÷ rough carats × 100. Cost per polished carat = (rough weight × rough cost + cutting and lab) ÷ polished carats. Profit = polished carats × average value − total cost.
Weight unit converter
Convert between carats, grams, tola, troy ounces, taels, baht and more.
How it is calculated
1 carat = 0.2 g · 1 tola = 11.6638 g · 1 troy ounce = 31.1035 g · 1 Hong Kong tael = 37.429 g · 1 Thai baht (gold) = 15.244 g · 1 pennyweight = 1.55517 g · 1 grain = 0.0647989 g.
Exchange rates are the day’s reference rates, for estimates only. Enter your own gold rate for the day.
Do this for every stone, automatically
E-Ratna prices, weighs and values your whole stock for you. See it in a free demo.