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Pull up your wallet using Sparrow Wallet and you can view the details of a UTXO (such as the size in vB).
If your UTXO is 140 vB and the fee to send is 100 sats/vB, then your fee for that one UTXO would be 140 * 100 = 14,000 sats.
If you have multiple UTXOs, you'd have to view the size of each of them, add them all together, then do the calculation.