1. What are float values?
Float values are the precise wear value of a skin. This value is a value between 0 and 1, where 0 is the least wear. The float values are mostly used in trading and trade-ups, and for most people the exterior quality is enough to know.
This is what the exterior on the skin is based on.
0 - 0.07 Factory New
0.07 - 0.15 Minimal Wear
0.15 - 0.38 Field-Tested
0.38 - 0.45 Well-Worn
0.45 - 1 Battle-Scarred
Note that not all skins have the full range of possible values. A AWP | Asiimov for instance, can only have values between 0.18 and 1, making
2. How can I calculate float values?
You can not calculate a skins float value, but it is possible to find. There are several services that can tell you your exact float values. Examples are CSGO Exchange and Steam Analyst.
In a trade-up contract on the other hand, you can calculate the float value of the item you will receive.
This is important if you're trying to "craft" a weapon. If the item you want has a full float value range (0-1) the formula is simple, its simply the average float value of all the low tier skin.
Wear on received item = Sum(All 10 trade up skins) / 10
If your trying to craft a weapon that does not have the full float value field, the formula is somewhat more complicated.
Wear on receiveed item = (MAX_FLOAT - MIN_FLOAT) * (Sum(All 10 trade up skins) / 10) + MIN_FLOAT