What is the correct way to calculate testnet BTC fees

It seems like fees have skyrocketed recently. I tried to send 20000 satoshi, but it cost me 27000 satoshi. Calculations are based on blockstream.info’s fee estimates https://www.blockstream.info/testnet/api/fee-estimates and calculated using: tx.virtualSize() * Quote Fee

My question is what is the correct way to calculate btc/testnet btc fees.