Items in the game don't have a carry weight as such. Instead, each item takes up a single inventory slot in your Xenosuit.

An example:

You have 3 air canisters, 300 bullets, and 2 rope in your inventory.

Each item of the same name is stacked and therefore only costs one inventory space. So in the above example, to carry all items, you will need 3 inventory slots. All items you come across in-game will require one slot in order to carry it.