Byte calculation for transaction fee?

[the.jack20]

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?

[1714053869]

1714053869

[1714053869]

1714053869

[1714053869]

1714053869

[1714053869]

1714053869

[TastyChillySauce00]

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".
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:

[Naokia980]

Transaction accelerator: viabtc.com/tools/txaccelerator/

It is free and really works.

[the.jack20]

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".
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:

No, I want to calculate it before I do it. After the transaction, I can check the sites like blocktrail.com or blockchain.info
But what I want to know is knowing how many bytes it is before processing. Then I would like to enter a reasonable fee using the average values at bitcoinfees.21.co

[~Bitcoin~]

How do we calculate the total number of bytes in a transaction we have done?

Most of the bitcoin wallets have fee recommendation system which will tell you how much fee will be enough to get confirmation within next block.

But if you like to calculate manually http://bitcoin.stackexchange.com/questions/1195/how-to-calculate-transaction-size-before-sending

If your transaction has in inputs and out outputs, the transaction size, in bytes will be:

in*180 + out*34 + 10 plus or minus 'in'
For example, this transaction has 40 inputs and 16 outputs. That gives us a transaction size of

40*180 + 16*34 + 10 +- 40
i.e. 7754 +- 40 bytes. The actual size is 7761 bytes.

I think this is correct calculation.

[the.jack20]

How do we calculate the total number of bytes in a transaction we have done?

Most of the bitcoin wallets have fee recommendation system which will tell you how much fee will be enough to get confirmation within next block.

But if you like to calculate manually http://bitcoin.stackexchange.com/questions/1195/how-to-calculate-transaction-size-before-sending

If your transaction has in inputs and out outputs, the transaction size, in bytes will be:

in*180 + out*34 + 10 plus or minus 'in'
For example, this transaction has 40 inputs and 16 outputs. That gives us a transaction size of

40*180 + 16*34 + 10 +- 40
i.e. 7754 +- 40 bytes. The actual size is 7761 bytes.

I think this is correct calculation.

How to find input and output values?
Where did the -40 come from during the calculation? Why-16 not used? What's the use of -40?
How do we determine the plus and minus selection criteria?