Weight Converter - Complete Guide

Weight/mass converter transforms between metric (grams, kilograms), imperial (pounds, ounces), and specialized units (stone, troy ounces). Critical for cooking, shipping, fitness tracking, jewelry, and international commerce where different weight systems are used.

How It Works

All weights convert through a base unit (grams or kilograms). Input value × conversion factor to base, then base × conversion factor to target. For example: 1 pound = 453.592 grams, so 2.5 pounds = 1133.98 grams = 1.134 kilograms.

Technical Details

The SI base unit for mass is the kilogram (kg). Key factors: 1 pound (lb) = 453.59237g (exact), 1 ounce (oz) = 28.349523g, 1 stone = 6.35029kg, 1 troy ounce = 31.1035g (for precious metals). Note: weight (force) vs mass (amount of matter) differ but are used interchangeably colloquially.

Common Use Cases

1. Cooking & Recipes: Convert between US recipes (cups/oz) and metric (grams).
   • Example: 8 oz flour = 226.8 grams
2. Fitness Tracking: Convert body weight between pounds and kilograms for different apps.
3. Shipping & Logistics: Calculate shipping costs when carriers use different weight units.
4. Precious Metals: Convert troy ounces (gold/silver) to grams or regular ounces.
   • Example: 1 troy oz gold = 31.1g

Code Examples

JavaScript Weight Converter

const weightToGrams = {
  gram: 1,
  kilogram: 1000,
  milligram: 0.001,
  pound: 453.59237,
  ounce: 28.349523125,
  stone: 6350.29318,
  'troy-ounce': 31.1034768,
  tonne: 1000000
};

function convertWeight(value, fromUnit, toUnit) {
  const grams = value * weightToGrams[fromUnit];
  return grams / weightToGrams[toUnit];
}

// Examples
convertWeight(1, 'pound', 'kilogram');      // 0.4536
convertWeight(1, 'troy-ounce', 'gram');     // 31.1035
convertWeight(70, 'kilogram', 'stone');     // 11.023

Convert through grams as intermediate. Handle troy ounces separately for precious metals.

Tips & Best Practices

• Quick estimate: 1 kg ≈ 2.2 lbs
• Troy ounces are used ONLY for precious metals
• UK body weight often uses stone
• Baking requires weight, not volume, for accuracy
• Shipping weights may include packaging (gross vs net)

Common Mistakes to Avoid

• Confusing troy ounces with regular ounces
• Using volume measures when weight is needed
• Forgetting tare weight for shipping
• Not accounting for local weight standards

When to Use This Tool

Use weight converter for cooking, fitness tracking, shipping calculations, precious metal transactions, and medical dosages based on body weight.

Frequently Asked Questions

What is the difference between ounces and troy ounces?

Regular ounce = 28.35g, troy ounce = 31.1g. Troy ounces are used for precious metals. A troy ounce is heavier but there are only 12 troy ounces in a troy pound.

How do I convert pounds to kilograms quickly?

Rough rule: divide pounds by 2.2. For more precision: pounds × 0.4536 = kilograms. Example: 150 lbs ÷ 2.2 ≈ 68 kg.

What is a stone?

A stone = 14 pounds = 6.35 kg. Still commonly used in UK/Ireland for body weight. Example: "I weigh 12 stone" = 168 lbs = 76.2 kg.

Why are cooking conversions sometimes different?

Cooking often uses volume (cups) which varies by ingredient density. 1 cup of flour ≠ 1 cup of sugar in weight. Use weight conversions for accuracy.

Get Started

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Last updated: June 27, 2026