Pounds to Kilograms & Ounces to Grams: Formula and Chart
Convert pounds to kilograms and ounces to grams with exact factors, worked examples, quick mental math, a ready chart, and stone for body weight.
Recipes, luggage limits, shipping labels, gym plates and doctor’s charts don’t all use the same units. If you live somewhere that uses kilograms and grams but read an American recipe or a UK health app, you’ll keep running into pounds, ounces and even stone. Getting the conversion slightly wrong can mean a flat cake, a surprise baggage fee, or a confusing medical form.
This guide gives you the exact conversion factors, the formulas in both directions with worked examples, a few mental-math shortcuts (and how far off they are), and a chart you can keep handy. If you just want the answer, the free Deftivo unit converter works it out in your browser.
The exact conversion factors
The pound is no longer defined separately. It is defined as an exact fraction of a kilogram, so these numbers are exact, not rounded:
| Unit | Exact value |
|---|---|
| 1 pound (lb) | 0.45359237 kg |
| 1 ounce (oz) | 28.349523125 g |
| 1 pound | 16 ounces |
| 1 stone (st) | 14 pounds (6.35029318 kg) |
The ounce here is the common “avoirdupois” ounce used for groceries, parcels and body weight. (Precious metals use a different “troy ounce”, which is not covered here.)
Formulas, both directions
Pounds to kilograms: kg = lb × 0.45359237
Kilograms to pounds: lb = kg ÷ 0.45359237 (about kg × 2.20462)
Ounces to grams: g = oz × 28.349523125
Grams to ounces: oz = g ÷ 28.349523125 (about g × 0.035274)
Worked examples
- 150 lb to kg: 150 × 0.45359237 = 68.0388555, so 68.04 kg.
- 70 kg to lb: 70 ÷ 0.45359237 = 154.3235835, so 154.32 lb.
- 12 oz to g: 12 × 28.349523125 = 340.1942775, so 340.19 g.
- 500 g to oz: 500 ÷ 28.349523125 = 17.6369809, so 17.64 oz.
When you have pounds and ounces together, such as 3 lb 6 oz, turn everything into ounces first (3 × 16 + 6 = 54 oz), then multiply: 54 × 28.349523125 = 1,530.87 g, or about 1.53 kg.
Quick mental math and how wrong it is
Sometimes you only need a rough figure. Here are common shortcuts and how much they drift from the exact answer:
| Shortcut | Example (exact answer) | Shortcut result | Error |
|---|---|---|---|
| lb ÷ 2 | 150 lb (68.04 kg) | 75 kg | about 10% too high |
| lb ÷ 2, then subtract 10% | 150 lb (68.04 kg) | 67.5 kg | about 0.8% too low |
| kg × 2.2 | 70 kg (154.32 lb) | 154 lb | about 0.2% too low |
| oz × 30 | 12 oz (340.19 g) | 360 g | about 6% too high |
| oz × 28 | 12 oz (340.19 g) | 336 g | about 1.2% too low |
“Halve it and take off a tenth” is the best balance of easy and accurate for pounds to kilograms. For ounces, × 28 is close enough for most cooking, but baking and medication doses deserve the exact factor.
Conversion chart
Every value below is calculated from the exact factors and rounded to two decimals.
Pounds to kilograms
| Pounds | Kilograms |
|---|---|
| 1 lb | 0.45 kg |
| 2 lb | 0.91 kg |
| 5 lb | 2.27 kg |
| 10 lb | 4.54 kg |
| 20 lb | 9.07 kg |
| 50 lb | 22.68 kg |
| 100 lb | 45.36 kg |
Ounces to grams
| Ounces | Grams |
|---|---|
| 1 oz | 28.35 g |
| 4 oz | 113.40 g |
| 8 oz | 226.80 g |
| 16 oz (1 lb) | 453.59 g |
Kilograms to pounds
| Kilograms | Pounds |
|---|---|
| 1 kg | 2.20 lb |
| 5 kg | 11.02 lb |
| 10 kg | 22.05 lb |
| 50 kg | 110.23 lb |
Weight ounces vs fluid ounces
This is one of the most common mix-ups. A weight ounce (oz) measures mass. A fluid ounce (fl oz) measures volume, meaning how much space something takes up. They are different units that happen to share a name.
| Measures | Approximate metric value | |
|---|---|---|
| Ounce (oz) | Weight | 28.35 g |
| US fluid ounce (fl oz) | Volume | 29.57 mL |
| Imperial (UK) fluid ounce | Volume | 28.41 mL |
You can’t convert fluid ounces to grams with a single number, because it depends on what you’re measuring. A fluid ounce of water, honey and flour all weigh different amounts. If a recipe says “8 oz flour”, it means weight; if it says “8 fl oz milk”, it means volume. Also note that US and UK fluid ounces are not the same size.
Body weight in stone
In the UK and Ireland, people often give body weight in stone and pounds, such as “11 st 4 lb”. To convert:
- Multiply the stone by 14 and add the extra pounds: 11 × 14 + 4 = 158 lb.
- Multiply by 0.45359237: 158 × 0.45359237 = 71.67 kg.
Going the other way, 80 kg ÷ 0.45359237 = 176.37 lb. Divide by 14: that’s 12 full stone (168 lb) with 8.37 lb left over, so about 12 st 8 lb. A single stone is 6.35 kg, which is a handy reference point.
How to convert weight with Deftivo
The unit converter runs entirely in your browser, so nothing you type is sent to a server.
- Open the Deftivo unit converter.
- Choose the Weight category.
- Type your number and pick its unit from the list, such as Pound (lb) or Ounce (oz).
- Read the table below: it shows the value in every weight unit at once, including kilograms, grams and stone.
To go the other way, pick Kilogram (kg) or Gram (g) as the unit instead. For stone-and-pounds values, convert them to total pounds first using the method above.
Tips and pitfalls
- Round at the end, not in the middle. If you round 0.45359237 to 0.45 and then multiply a large number, the error grows. Use the full factor and round the final answer.
- Don’t treat “lb” and “lbs” as different. Both mean pounds; “lbs” is just an informal plural.
- Check which ounce you have. A label showing “fl oz” is volume, not weight.
- Watch out for kitchen scales set to the wrong unit. Many scales can switch between grams and ounces, and the display may look similar.
- For shipping and luggage, round up. Carriers often charge by the next whole unit, so a parcel at 22.1 kg may count as 23 kg.
- Body weight on medical forms should usually be given exactly as the form asks; don’t mix stone and kilograms in the same field.
FAQ
How many kilograms is one pound exactly?
One pound is exactly 0.45359237 kg. This value is fixed by definition, so it never changes. For everyday use, 0.45 kg or 0.454 kg is usually close enough.
How many grams are in an ounce?
One ounce is exactly 28.349523125 g, which rounds to 28.35 g. Sixteen ounces make one pound, or about 453.59 g. This applies to weight ounces, not fluid ounces.
Is a fluid ounce the same as an ounce?
No. A fluid ounce measures volume, while an ounce measures weight. How many grams a fluid ounce weighs depends on the substance, and US and UK fluid ounces are slightly different sizes.
How do I convert stone to kilograms?
Multiply the number of stone by 14 to get pounds, add any extra pounds, then multiply by 0.45359237. For example, 10 st is 140 lb, which equals 63.50 kg. One stone on its own is about 6.35 kg.