What is 8.6 lb
Our converter does its sums properly.
We give the results in stones, pounds (lb) and ounces (oz), not as decimal fractions of a pound (8.nn lb).
If you need the actual formulas so you can do your own conversions to scientific accuracy, Wikipedia has a brilliant article covering Conversion of Units that encompasses every a huge array of calculations for every conceivable unit of measurement
I only shown the units with more than 10 formulas, showing: (unit of measurement: number of formulas) in the Wiki article
length:69, area:36, volume:98, density:13, time:38, speed:17, acceleration:12, force:1a, pressure:22, energy:42, power:27
That should be enough to keep you entertained for a while!