What is a txn and how does it affect fees on Bitcoin? A (txn) transaction on the Bitcoin network has fees determined by two main factors: the size of the transaction measured in virtual bytes (vB) and the fee rate chosen by the sender. Currently, the minimum fee is set at 1 sat/vB. An important thing to know is that the size of a txn will increase when you add more inputs (inputs) or outputs (outputs). For example, if you create a transaction with 5 inputs instead of 1 input, the txn size will be larger, resulting in higher fees at the same sat/vB fee rate. Therefore, to optimize transaction costs, users need to consider the number of inputs and outputs in each txn.