Kilograms and Pounds Explained

The defined pound

The international avoirdupois pound is 0.45359237 kg exactly. That is the pound on a US bathroom scale, a shipping API and a bag of flour marked in pounds. Kilograms to pounds is a divide by that constant. Pounds to kilograms is a multiply. KG to LBS and LBS to KG are the same definition in opposite directions.

The casual “times 2.2” shortcut is about 0.2% low. Fine for a mental check of a suitcase, poor for repeating conversions that need to invert cleanly.

Body weight and luggage

70 kg is 154.3236 lb. 23 kg of checked luggage is 50.7063 lb — near the “50 pound” cap some US carriers print, which is actually 22.68 kg. Convert the number on the tag you have; do not assume the marketing round number matches the other unit.

Birth weight written 7 lb 8 oz is 7.5 lb because there are 16 ounces in this pound. That is 3.4019 kg. Ounces here are mass ounces, not fluid ounces.

Gym plates are not twins

A 20 kg plate is 44.0925 lb. A 45 lb US plate is 20.4117 kg. Loading “two plates a side” means different kilograms depending on which plates are on the bar. Convert the stamp, then add the bar.

What this pound is not

Troy pounds (12 troy ounces) are for precious metals. A troy ounce is about 31.10 g; a kitchen ounce is 28.35 g. Grams to ounces uses the kitchen ounce. Fluid ounces are volume — see millilitres to US fluid ounces. Length and temperature are different guides: centimetres to inches and Celsius and Fahrenheit.