This is for items under level 60 using the current scaling mechanics.
You may also see items with stats and required levels that are not using the scaling mechanics/are still dropping at their old levels, particularly from chests and possibly some dungeons.
World Drop BoE Weapon epics can only drop at required levels ending with 3 and 8 and will be +13 ilevels over the required level.
For example, an axe might drop at a required level of 33, 38, 43, 48 and would have ilevels of 46, 51, 56, 61 respectively.
World Drop BoE Armor epics can only drop at required levels ending in 2 and 7 and will be +13 ilevels over the required level.
Instance/Mob Specific epics will drop at the player's current level as the required level and will be +12 ilevels over the required level.
World Drop BoE Weapon blues can only drop at required levels ending in 2 or 7 and will be +8 ilevels over the required level. (Max ilvl 25 @ level 19)
World Drop BoE Armor blues can only drop at required levels ending with 0 and 5 and will be +8 ilevels over the required level. (Max ilvl 23 @ level 19)
Instance/Mob Specific blues will drop at the player's current level as the required level and will be +6 ilevels over the required level. (Max ilvl 25 @ level 19)
(Also keep in mind that there are likely minimum required levels for certain drops.)