KAS you need

What a launch or a buy needs in KAS.

You trade on Kasseal with KAS from your own wallet. When a launch or a buy needs more KAS than your wallet holds, the app says how much is missing.

How much do I need?

A buy needs the price of the tokens, the 1% curve fee, a small network fee and a 5 KAS deposit for the new token UTXO (returned when you sell). See Token UTXOs and deposits.
A launch needs the network fees of two transactions and the KAS the token’s new cells carry; the Create screen shows the exact amount before you sign. See What a launch costs.