A very interesting article concerning Bitcoin transaction fees can be found here: Bitcoin Transaction Fees Explained [Complete Guide]

Websites to calculate the optimal Bitcoin transaction fees are e.g.:

https://Estimatefee.com "is a simple website that calculates the cost (in satoshis and USD) for a bitcoin transaction based on how much of hurry you are to move your coins from A to B."

https://Bitcoinfees.info "displays slow/medium/fast fees in USD with no muss and no fuss."

Source: https://bitnewsbot.com/how-to-calculate-bitcoin-transaction-fees-when-youre-in-a-hurry/