Hi,
HikaShop just allow to select a product quantity which is a no-decimal number.
You can use variants in order to create several different weights for the selection or, thanks to customization, you can override some views in order to add new features.
I already done before by other customer, some clients have modified their product page in order to not display the classical "quantity selector" but instead, displaying a drop down list selection.
The list make the link between the weight and the quantity.
0.5Kg would be quantity 1
1.0Kg would be quantity 2
etc
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.