Gift card balance

The balance on an iTunes Store gift card itself is either what it says on the face of the card (if present), or nothing because it has already been redeemed. The only way to check is to try redeeming the card and check your store balance. Of course that will transfer any balance on the card entirely to your Apple ID so then the card balance will be zero.

Redeem your App Store & iTunes Gift Card - Apple Support - https://support.apple.com/HT201209

The best way to check the balance would be to visit https://www.apple.com/shop/gift-cards

Tap on Check Balance at the top right of that screen

Hope this helps ;)

the balance on my card

yes

That does not apply to iTunes gift cards. ;-)