Stock by Weight

[ALFO]

We stock it in bulk i.e. Stock = 2000g of Earl Grey and we can sell as 20 x 100g packs or 10 x200g packs depending.

[kobra]

set the product up as 1g and priced by attributes

create the attribute name, like package or another title you prefer and create attribute values linked to it(100g & 200g) as either radio buttons or as a drop down & set the minium at 100g. Check other settings and set the pricing attributes to correctly calc the price.