Calculating the value of gold involves understanding the relationship between the global spot price, the weight of the metal, and its purity level. The global standard for trading gold is measured in US Dollars per Troy Ounce (oz t).
The Core Formula
To calculate the rate manually, you need to normalize the weight and adjust for purity. Here is the mathematical process:
Gold Value = (Spot Price ÷ 31.1035) × Weight in Grams × (Karat ÷ 24)
Step-by-Step Calculation Guide
Determine the Spot Price: Check the current live market rate for gold (XAU/USD). For example, $2,000 per troy ounce.
Convert to Grams: Since spot prices are usually per ounce, divide the price by 31.1035 to get the price per gram of pure 24K gold.
Adjust for Purity: Gold jewelry is rarely 100% pure. Multiply the price per gram by the purity ratio (Karat/24).
24K = 100% (1.0)
22K = 91.6% (0.916)
18K = 75.0% (0.750)
Multiply by Weight: Multiply the adjusted price per gram by the total weight of your item in grams.
Add Making Charges: Jewelers add a fee for labor and design, usually between 5% to 20% of the gold value.
Gold Weight Conversion Table
Understanding different units of measurement is crucial when buying gold internationally.
Unit
Gram Equivalent
Usage
1 Troy Ounce
31.1035 grams
International Trading
1 Tola
11.6638 grams
India, Pakistan, Singapore
1 Pennyweight (dwt)
1.555 grams
Dental, Jewelry (USA)
1 Kilogram
1000 grams
Bullion Bars
Why do Karats Matter?
The "K" or Karat indicates how much pure gold is in the alloy. The rate changes drastically based on this number.
24K: Pure gold, soft, used for investment bars/coins.
22K: Durable, standard for high-quality jewelry.
18K: Very durable, used for diamond settings and watches.
function calculateGoldRate() {
// 1. Get Input Values
var spotPrice = document.getElementById('spotPrice').value;
var weight = document.getElementById('goldWeight').value;
var unit = document.getElementById('weightUnit').value;
var karat = document.getElementById('karat').value;
var makingChargesPercent = document.getElementById('makingCharges').value;
// 2. Validate Inputs
if (spotPrice === "" || weight === "" || isNaN(spotPrice) || isNaN(weight)) {
alert("Please enter a valid Spot Price and Weight.");
return;
}
spotPrice = parseFloat(spotPrice);
weight = parseFloat(weight);
makingChargesPercent = parseFloat(makingChargesPercent);
if (isNaN(makingChargesPercent)) {
makingChargesPercent = 0;
}
// 3. Define Constants
var GRAMS_IN_OUNCE = 31.1034768;
var GRAMS_IN_TOLA = 11.6638038;
var GRAMS_IN_DWT = 1.55517384;
// 4. Convert Input Weight to Grams (Standardization)
var weightInGrams = 0;
if (unit === "gram") {
weightInGrams = weight;
} else if (unit === "ounce") {
weightInGrams = weight * GRAMS_IN_OUNCE;
} else if (unit === "tola") {
weightInGrams = weight * GRAMS_IN_TOLA;
} else if (unit === "kg") {
weightInGrams = weight * 1000;
} else if (unit === "dwt") {
weightInGrams = weight * GRAMS_IN_DWT;
}
// 5. Calculate Price Per Gram (24K Base)
var pricePerGram24k = spotPrice / GRAMS_IN_OUNCE;
// 6. Calculate Purity Factor
var purityFactor = parseFloat(karat) / 24;
// 7. Calculate Pure Gold Value
var goldValue = pricePerGram24k * purityFactor * weightInGrams;
// 8. Calculate Making Charges
var makingChargesAmount = goldValue * (makingChargesPercent / 100);
// 9. Total Value
var totalValue = goldValue + makingChargesAmount;
// 10. Display Results
document.getElementById('resBasePrice').innerText = "$" + pricePerGram24k.toFixed(2);
document.getElementById('resWeight').innerText = weightInGrams.toFixed(2) + " g";
document.getElementById('resPurityValue').innerText = "$" + goldValue.toFixed(2);
document.getElementById('resMakingCharges').innerText = "$" + makingChargesAmount.toFixed(2);
document.getElementById('resTotal').innerText = "$" + totalValue.toFixed(2);
// Show result div
document.getElementById('results').style.display = 'block';
}