General

Using DOT skills works better though (burn, poison, etc. that do DOT damage on mobs is calculated by max damage * DOT%)

Easiest way is to hit weak mobs with your regular attack, find what the most damage you can do is

then factor in your max crit damage and you should be able to get your range

For example, if you did 5m damage with 90% max crit damage, your range should be 5m/1.9 =2.63m

Mostly its calculated with the range formula and substituting your own values in for atk, luk, dex, total damage, %atk and weapon multiplier. Since your a shad though, I'd assume venom damage works fine seeing as it takes your top range (I believe?) So just divide your venom damage to get what 100% damage is (I don't know how much %dmg venom does lol) and that should be your top range

I think using a normal attack on a low defense monster would give a rough estimate. Otherwise, just use the standard range formula which can be found here: http://strategywiki.org/wiki/MapleStory/Formulas