To check the amount of Bitcoin (BTC) available in your own Kraken account, you must first log in to your Kraken account. Then select Kraken Pro at the top of the menu.
Then select Portfolio from the menu at the top
Then scroll down the page until you see Bitcoin (BTC) balance
Here you can see that the available amount of BTC (available balance) in this example is 0.1621504 BTC. In this example, this is lower than the balance of 0.25336 BTC. This has to do with any open limit sell orders.