Manytox (player) on calculating expand:

• Expand multiplies volume by a factor of 1 + ((Expand ^ 2 )* 0.0004).
• Each size axis value gets multiplied by the cube root of that, then gets rounded down to the lower integer.
• For liquid containers, size won't change, but volume will be multiplied too.
• Size values also have a ceiling with expand, 1200, which actually reduces the size value for a couple of items. But for most usages that won't matter.
• Keep in mind cast powers have decimals, and the value you see is rounded down.
• You can have two containers that display the same expand cast, but when you get to testing their volumes (or even sizes!) empirically they will be slightly different.
• Runes for size and volume get applied before expand, but the order does matter because in both occasions the values get rounded down, since it is converting a float into an int.
• Lastly, for rough calculations, 50 expand is x2 volume, 100 expand is x5 vol, and 113 expand is my favorite number, 6.1076.