What is the conversion fee for crypto?

Excuse me, could you please clarify what the conversion fee for cryptocurrency entails? I'm interested in understanding the financial implications of converting one digital asset to another, say from Bitcoin to Ethereum. Are there standard rates that apply across the board, or does it vary depending on the exchange platform or the specific cryptocurrencies involved? Additionally, are there any hidden fees or charges that I should be aware of before initiating a conversion? Your insights would be greatly appreciated.