I've been using Paybis's coin calculator https://paybis.com/usd-coin-calculator/ for these conversions - it shows the exact amount you'll receive after all fees in real time. Last week I checked a 1,000 USDC to ETH conversion and it displayed both the estimated ETH and the exact fee breakdown before I committed.
What makes it useful is how it accounts for payment method differences. Bank transfers show lower fees than credit card purchases right in the calculation. The rates update constantly to match market prices. I've found it's typically within 0.5% of the final amount when you complete the transaction.
