I use the Paybis Bitcoin Calculator regularly and find it super helpful! It gives me real-time price calculations so I know exactly how much BTC I'll get for my money before making a trade. The interface is simple - you just enter the amount and it shows you the conversion instantly, including any fees. Here's the one I use: paybis.com/bitcoin-calculator/ . It's been great for quick calculations without needing to do the math manually every time.