What this converter does
This tool changes a weight from pounds and ounces into kilograms, or from kilograms back into pounds and ounces. Type your number and the answer appears right away. Pounds are the everyday weight unit in the United States. Kilograms are used almost everywhere else, and in science, medicine, shipping and most product labels.
People need a pounds to kg converter for many reasons: filling in a form that asks for body weight in kilograms, checking a luggage limit on an international flight, following a recipe from another country, or reading a baby's birth weight. The tool also shows grams, and for kilograms it shows ounces and stone, so you can pick the unit your task needs.
How to use it
- Choose the direction. "Pounds and ounces to kilograms" is the default. Pick the second option to go from kilograms to pounds and ounces.
- Type the numbers. For a weight such as 7 lb 8 oz, enter 7 in the pounds box and 8 in the ounces box. If you only know pounds, leave ounces at 0.
- Choose the number of decimal places. One decimal place is enough for most uses. Use three if you are weighing small items such as a newborn baby or a parcel.
- Read the results. The main answer is shown in large type, with the other units below it.
Negative weights are not accepted, because a weight cannot be less than zero.
The conversion formula
The relation between pounds and kilograms is not an approximation. Since the international agreement of 1959, one pound has been defined as exactly 0.45359237 kilograms. The National Institute of Standards and Technology (NIST) lists this factor in its guide to the International System of Units.
kilograms = pounds × 0.45359237
pounds = kilograms ÷ 0.45359237
1 pound = 16 ounces
1 stone = 14 pounds
To convert pounds and ounces together, first change everything into pounds: total pounds = pounds + ounces ÷ 16. Then multiply by 0.45359237. For 7 lb 8 oz, that is 7 + 8 ÷ 16 = 7.5 pounds, and 7.5 × 0.45359237 = 3.402 kg (rounded to three places).
Going the other way
To turn kilograms into pounds, divide by 0.45359237, or multiply by about 2.2046. For 68 kg, 68 ÷ 0.45359237 = 149.9 pounds. The part after the decimal point can be turned into ounces by multiplying it by 16. That is why the tool shows 68 kg as 149 pounds and about 14.6 ounces.
A quick mental shortcut
To estimate kilograms from pounds, cut the number in half and then take off a tenth of that half. For 150 pounds, half is 75, a tenth of 75 is 7.5, and 75 - 7.5 = 67.5 kg. The exact answer is 68.04 kg, so the shortcut is close but a little low. To go the other way, double the kilograms and add 10 percent. Use the converter when you need a precise number.
Worked examples
| Starting value | Calculation | Result |
|---|---|---|
| 1 pound | 1 × 0.45359237 | 0.454 kg |
| 10 pounds | 10 × 0.45359237 | 4.54 kg |
| 7 lb 8 oz | 7.5 × 0.45359237 | 3.402 kg |
| 150 pounds | 150 × 0.45359237 | 68.04 kg |
| 180 pounds | 180 × 0.45359237 | 81.6 kg |
| 200 pounds | 200 × 0.45359237 | 90.7 kg |
| 50 kg | 50 ÷ 0.45359237 | 110.2 pounds |
| 70 kg | 70 ÷ 0.45359237 | 154.3 pounds |
| 100 kg | 100 ÷ 0.45359237 | 220.5 pounds |
Notice that a kilogram is more than twice as heavy as a pound. One kilogram is about 2.2 pounds.
Where these units are used
The United States still uses pounds and ounces for body weight, groceries, mail and many packages. The United Kingdom uses a mix: people often give body weight in stone and pounds, while shops and doctors mostly use kilograms. Most other countries use only the metric system. That is why a passport form, a medical chart or an airline in another country may ask for kilograms while you think in pounds.
Gym weights, luggage limits and shipping rates are often quoted in both units. A common airline checked bag limit is expressed as 50 pounds in the US and 23 kilograms in many other places, and the two numbers are close but not identical. Being able to move between the two systems saves mistakes when you pack, ship or order goods.
Rounding tips
For body weight, one decimal place is plenty. For baking, shipping small parcels or checking a baby's weight, two or three decimal places are more useful. The converter rounds only at the very end, so rounding errors do not build up. Remember that a bathroom scale is rarely accurate to better than a few tenths of a kilogram, so extra decimals do not make a measurement more reliable.
Pounds, ounces and stone
Sixteen ounces make one pound, and fourteen pounds make one stone. Stone is used in the UK and Ireland for body weight, and almost nowhere else. When you convert kilograms, the tool shows the stone and pounds split using whole pounds, so 68 kg becomes 10 stone 9 pounds.
The ounce used for weight here is the avoirdupois ounce. Do not confuse it with the fluid ounce, which measures volume, or the troy ounce used for precious metals such as gold. This converter handles the everyday weight ounce only.
Frequently asked questions
- How many kilograms are in a pound?
- Exactly 0.45359237 kilograms. This is a definition, not a rounded measurement.
- How do I convert pounds to kg by hand?
- Multiply the number of pounds by 0.45359237. For example, 20 pounds × 0.45359237 = 9.07 kg.
- How do I convert pounds and ounces to kg?
- Divide the ounces by 16 and add that to the pounds. Then multiply the total by 0.45359237. For 10 lb 8 oz, 10.5 × 0.45359237 = 4.76 kg.
- What is 70 kg in pounds?
- About 154.3 pounds, which is 154 pounds and about 5.2 ounces.
- Is the conversion exact?
- Yes. The factor of 0.45359237 is exact, so only the displayed result is rounded, to the number of decimal places you choose.
- Is "lbs" the same as pounds?
- Yes. The abbreviation "lb" comes from the Latin word libra. People often write "lbs" for more than one pound, and both mean the same unit.
Things to keep in mind
This converter changes units only. It does not tell you whether a weight is healthy, how much medicine to give, or whether a package meets a shipping limit. For medical or legal forms, follow the instructions given by the organization that asks for the number, and ask a health professional about any health question. Also, a person's weight can vary noticeably over the course of a day, so small differences in a result are normal.