Normal BTC transaction does not consider number of inputs when calculating fee.

[snowkidind]

There is no way to see how many bytes a transaction is, in order to externally calculate how many sats you should send to get an appropriate rate on a transaction.

Recently I sent a transaction with high priority, but it had four inputs, (i was unaware of this) and thus the tx size was 631 Bytes whereas I (had to) guessed a "normal" transaction size of 400 bytes, thinking it was more than plenty.

At the time, using mempool.observer the rate should be 85 - 115 sats per byte max to get mined in a decent timeframe, but the additional inputs caused the outgoing transaction to weigh in at 41 sats per byte which will possibly take months to mine.

There is also no way to increase speed or cancel the transaction from the mempool either through FW.

This occurred in FW Desktop mac 0.9.26