What is the best way to manage inventory when an item is purchase in Kg but sold in multiple options such as 0.25kg, 0.50kg, 5kg etc?

What is the best way to manage inventory when an item is purchase in Kg but sold in multiple options such as 0.25kg, 0.50kg, 5kg etc?

Hello,

I am trying to understand what is the best way to manage the situation described below:

Lets assume the item we sell is Onion which we purchase in Kg (Kilo Grams). Now, on our front end website, we want to sell variants in 0.5kg, 1.0kg, 2.0kg, 5.0kg and 10.0kg. 

I have tried creating multiple item attributes which solves the first part of the problem,.i.e having multiple variants of the products. However, I am not able to understand how to manage the impact on inventory. 

The purchase entry is made for any one variant, so lets assume, we purchased 1000kg of onion and inventory is updated accordingly. Now customer place an order for 0.5kg from our website, the item level inventory on zoho invenotry for item Onion 0.5Kg is '0' (zero). 

Is there any way to deduct is 0.5kg from inventory of 1000kg in stock ?

Greatly appreciate help on this query!