Whether you are following a strength-training program, logging meals in a nutrition app, or adapting an international recipe, you will almost certainly run into pounds when you need kilograms — or the other way around. This lb to kg conversion calculator turns pounds, ounces, or stone into kilograms, grams, or milligrams in a single step. It is built for anyone who works with food weights and body-weight data on a regular basis.
The tool uses the internationally accepted definition of the avoirdupois pound: exactly 0.45359237 kilograms. That means your conversions are consistent with food labels, medical standards, and official weighing applications. You can adjust decimal places, view equivalent gram and ounce values, and use the quick-fill buttons to test common portions like 100 lb or 1 st.
No need to memorize conversion factors or flip between websites. Enter a value, choose the output unit, and press Convert to get a clean, accurate result instantly.
⚖️ Pounds to Kilograms Conversion
Convert pounds (lb), ounces (oz), or stone (st) to kilograms, grams, or milligrams.
How to Use This Converter
This tool is designed for quick, accurate weight conversions in the kitchen, at the gym, or while tracking a nutrition plan. Type the weight into the first field, then use the dropdown to tell the calculator whether that number is in pounds, ounces, or stone. Next, pick the metric unit you want in the output — kilograms, grams, or milligrams — and choose how many decimal places to display. Press Convert to see the main result, along with the same weight in grams, ounces, and stone. The Reset button clears all fields and starts a new conversion.
The quick-fill buttons below the inputs insert common examples so you can check several portion sizes quickly. If you are tracking food portions, you will usually want kilograms or grams, because nutrition labels and food databases often list weights in metric units. After converting, look at the three secondary values as well: grams, ounces, and stone. Seeing the same weight in several formats helps you spot-check package labels and compare entries from different countries.
The Conversion Formula
The international avoirdupois pound is defined as exactly 0.45359237 kilograms. This is the standard used for trade, health, and nutrition in most countries. To convert pounds to kilograms, multiply the pound value by 0.45359237:
For example, 10 lb becomes 10 × 0.45359237 = 4.5359237 kg. The same factor works in reverse: divide a kilogram value by 0.45359237 to get pounds. Since 1 pound equals 16 ounces and 1 stone equals 14 pounds, the calculator also uses the linked conversion factors 1 oz = 0.028349523125 kg and 1 st = 6.35029318 kg. These relationships come from the internationally agreed definition of the pound, which has been in use since 1959.
Worked Examples
Example 1 — 150 lb to kg: 150 × 0.45359237 = 68.0388555 kg, which rounds to 68.04 kg. This is a common body-weight benchmark.
Example 2 — 8 oz to grams: 8 oz is half a pound. In kilograms: 8 × 0.028349523125 = 0.226796185 kg. Multiplying by 1000 gives 226.80 g. This is useful when a recipe lists an ingredient in ounces but your scale measures grams.
Example 3 — 12 st to kg: 12 × 6.35029318 = 76.20351816 kg, or about 76.20 kg. If your bathroom scale reads stone, this calculator can translate that to the unit your health app expects.
Reference Table: Common lb to kg Conversions
| Pounds (lb) | Kilograms (kg) | Grams (g) |
|---|---|---|
| 1 lb | 0.45 kg | 453.59 g |
| 5 lb | 2.27 kg | 2267.96 g |
| 10 lb | 4.54 kg | 4535.92 g |
| 25 lb | 11.34 kg | 11339.81 g |
| 50 lb | 22.68 kg | 22679.62 g |
| 100 lb | 45.36 kg | 45359.24 g |
| 150 lb | 68.04 kg | 68038.86 g |
| 200 lb | 90.72 kg | 90718.47 g |
Values in the table are rounded to two decimal places for kg and two for g. Use the calculator for a more precise result at higher pound values.
Common Mistakes to Avoid
- Using rounded constants too early. If you use 0.45 instead of 0.45359237, a 200 lb weight will be off by about 0.72 kg — enough to matter when tracking macros or medication-related weights.
- Confusing weight ounces with fluid ounces. This calculator converts avoirdupois ounces (a mass measurement), not fluid ounces (a volume measurement). One fluid ounce of water weighs about 1.04 oz, but the two units are not interchangeable for other foods.
- Forgetting to switch the input unit. The quick-fill pills set both the value and the unit, but if you type a number manually after selecting ounces, the result is in kilograms or grams based on the unit shown in the dropdown. Always glance at the unit selector before converting.
- Ignoring decimal places when logging food. For a single portion the difference is tiny, but when you log several foods daily, rounding every entry to whole kilograms can add noticeable error.
Precision Notes
Because the pound is defined exactly in terms of the kilogram, this conversion is mathematically exact; the only imprecision comes from rounding your displayed result. Choose more decimal places for scientific or clinical uses and fewer for everyday cooking. The built-in output also shows equivalent grams, ounces, and stone for the same input, so you can see the weight in several formats without retyping anything.
For weights below 1 lb, milligrams may be overkill; grams are more practical. On the other hand, when working with very small quantities like yeast or salt, choose 3-4 decimal places in kilograms or switch to milligrams. The calculator keeps all intermediate math in kilograms using exact definitions, so the only rounding is in the final displayed number.