At https://bitcoinfees.21.co/ we find out how much we should send satoshi per byte, on average, for our transactions to be approved.
How do we calculate the total number of bytes in a transaction we have done?
In this case, you're talking about the transaction you "have done".How do we calculate the total number of bytes in a transaction we have done?
Simply check your transaction using blockchain explorers such as https://blockchain.info/tx/INSERT_TXID_HERE. Once you have done inserting your TXID, you will see some information regarding your transaction and there you can find the size of your transaction.
Example:
