The exact pound
One pound is exactly 0.45359237 kg, by the 1959 agreement that also fixed the inch. An ounce is a sixteenth of that, 28.349523125 g, and a stone is 14 pounds, 6.35029318 kg. Because those are definitions, a pound typed in returns exactly 0.45359237, and 1 kg comes out at 2.20462262185 lb.
Body weight in stone
In the UK body weight is often given in stone and pounds, like 11 st 4 lb. The converter takes one unit at a time, so turn it into pounds first: 11 × 14 + 4 = 158 lb, which is 71.67 kg. To go from kilograms to stone and pounds, convert to pounds and divide by 14: 80 kg is 176.37 lb, which is 12 st 8.37 lb.
Three kinds of ton
A tonne (metric ton) is 1,000 kg. A US ton, the short ton, is 2,000 lb or 907.18 kg. An imperial ton, the long ton used in the UK, is 2,240 lb or 1,016.05 kg. All three are in the list, so check which one a figure means before converting.
One pair at a time
The pairs people look up most have a page each, opened on that pair with a table of common values: kg to lbs, lbs to kg, oz to Grams and Grams to oz.
Questions
Is it weight or mass?
Strictly, kilograms and pounds measure mass, and weight is the force gravity puts on it. In everyday use, and on every scale, the two words mean the same thing, and the numbers here are the ones a scale shows.
How many grams are in an ounce?
28.349523125 exactly, usually rounded to 28.35. That is the ordinary (avoirdupois) ounce used for food. The troy ounce used for gold and silver is 31.1035 g and is not in the list.