The Quick Answer
To convert between weight units, multiply by a conversion factor. The most common ones:
| Conversion | Multiply by | Example |
|---|---|---|
| kg → lbs | 2.20462 | 70 kg = 154.32 lbs |
| lbs → kg | 0.45359 | 180 lbs = 81.65 kg |
| g → oz | 0.03527 | 250 g = 8.82 oz |
| oz → g | 28.3495 | 6 oz = 170.10 g |
| stone → kg | 6.35029 | 12 st = 76.20 kg |
| kg → stone | 0.15747 | 90 kg = 14.17 st |
All factors above follow the international avoirdupois standard, which is the system used for everyday weight measurements in the US, UK, and most of the world.
How the Conversion Works
Every common weight unit is defined as a fixed number of grams. To convert from unit A to unit B:
result = value × (gramsPerUnitA / gramsPerUnitB)
Exact Definitions in Grams
| Unit | Symbol | Grams (exact) |
|---|---|---|
| Gram | g | 1 |
| Kilogram | kg | 1,000 |
| Ounce | oz | 28.349523125 |
| Pound | lb | 453.59237 |
| Stone | st | 6,350.29318 |
| Metric ton | t | 1,000,000 |
These values are exact by international agreement, not approximations.
Step-by-Step Examples
Example 1: Convert 75 kg to Pounds
- Look up the factors: 1 kg = 1,000 g; 1 lb = 453.59237 g
- Calculate: 75 × (1,000 / 453.59237) = 75 × 2.20462 = 165.35 lbs
Example 2: Convert 200 grams to Ounces
- Factors: 1 g = 1 g; 1 oz = 28.349523125 g
- Calculate: 200 × (1 / 28.349523125) = 200 × 0.03527 = 7.05 oz
Example 3: Convert 11 Stone to Kilograms
- Factors: 1 st = 6,350.29318 g; 1 kg = 1,000 g
- Calculate: 11 × (6,350.29318 / 1,000) = 11 × 6.35029 = 69.85 kg
Example 4: Convert 2.5 Metric Tons to Pounds
- Factors: 1 t = 1,000,000 g; 1 lb = 453.59237 g
- Calculate: 2.5 × (1,000,000 / 453.59237) = 2.5 × 2,204.62 = 5,511.56 lbs
Metric vs Imperial: Which Countries Use What
Metric system (grams, kilograms, metric tons) is the international standard. Nearly every country uses it officially, including all of Europe, Asia, Africa, and South America.
Imperial / US customary (ounces, pounds) is the everyday system in the United States. Groceries, body weight, shipping, and recipes commonly use pounds and ounces.
Stone is specific to the UK and Ireland, used almost exclusively for body weight. One stone = 14 pounds. A person might say "I weigh 11 stone 4" meaning 11 st + 4 lbs = 158 lbs = 71.67 kg.
Common Mistakes
1. Confusing Troy Ounces with Avoirdupois Ounces
The everyday ounce (avoirdupois) weighs 28.35 g. The troy ounce, used for precious metals like gold and silver, weighs 31.10 g. If you're converting jewelry or bullion weights, use troy ounces. For everything else — food, body weight, shipping — use avoirdupois.
2. Mixing Up Short Tons, Long Tons, and Metric Tons
| Ton type | Pounds | Kilograms | Used where |
|---|---|---|---|
| US short ton | 2,000 | 907.18 | United States |
| UK long ton | 2,240 | 1,016.05 | Historical UK use |
| Metric ton (tonne) | 2,204.62 | 1,000 | International standard |
When someone says "ton" without qualification, check the context. In international trade and science, it almost always means metric ton.
3. Rounding Too Early
If you're chaining conversions (e.g., ounces → grams → kilograms), use full precision at each step and only round the final result. Rounding intermediate values compounds error.
4. Using Fluid Ounces for Weight
Fluid ounces (fl oz) measure volume, not weight. One fluid ounce of water weighs about 29.57 g, while one weight ounce is 28.35 g. For liquids, the weight depends on density — honey is heavier per fluid ounce than water.
Quick Mental Math Shortcuts
These approximations are useful when you don't have a calculator handy:
- kg to lbs: multiply by 2.2 (accurate to within 0.2%)
- lbs to kg: divide by 2.2, or multiply by 0.45
- oz to g: multiply by 28 (underestimates by ~1.2%)
- stone to kg: multiply by 6.35, or multiply by 6 and add half
- stone to lbs: multiply by 14
When Precision Matters
For most everyday tasks — cooking, fitness tracking, shipping estimates — rounding to one or two decimal places is more than sufficient.
Precision matters in:
- Laboratory science: measurements often need milligram or microgram accuracy
- Precious metals trading: troy ounce pricing means even small rounding errors affect value
- Pharmaceutical dosing: medication is measured in exact milligrams
- International shipping: customs declarations require accurate weights in kilograms
For these use cases, use a converter that preserves full decimal precision, and always verify which unit standard applies.
Try It
Use the Weight & Mass Converter to convert between all six units instantly. Enter a value once and see every equivalent — grams, kilograms, ounces, pounds, stone, and metric tons — in a single table.
For kitchen-specific conversions (cups, tablespoons, milliliters), see the Cooking Measurement Converter. For ounce-to-gram conversions with common presets, try the Ounces to Grams Converter.