Estimating transaction size in bytes per element of the transaction

[IfPtr]

Hello guys,

I have been reading about transactions recently and I am interested in understanding how the size of a transaction is influenced by its building elements.
So for example we know that a transaction contains:

• a certain number of inputs
• a cetrain number of outputs
• a locking scrpit (scriptPubKey)
• an unlocking script (scriptSig)

... and other elements. What I would like to know is how much each of the elements contributes to the total size of the transaction. So for example how many bytes are the typical scripts? Do they vary in size? Do inputs have a (approximately) fixed size in bytes? Do outputs have a (approximately) fixed size in bytes? Is everything thus a simple game of addition?

Thank you very much for taking the time to read my question!

[btj]

Size of transaction = Number inputs * (Input Size) + Number of outputs * (Output Size) + 10 Bytes extra fixed fee required for the framework of the transaction

How to get the P2PKH input size ?

PREVOUT  + SCRIPTSIG + sequence = 32 + 4 + 1 + 1 + (71 or 72) + 1 + 33 (Compressed) + 4 = 147 or 148

PREVOUT: hash (32 bytes)
         index (4 bytes)
SCRIPTSIG: length (1 byte)
           CONTENTS: push opcode (1 byte)
                     signature (71 or 72 bytes)
                     push opcode (1 byte)
                     pubkey (33 bytes for compressed, 65 for uncompressed)
sequence (4 bytes)

Source: https://bitcoin.stackexchange.com/questions/48279/how-big-is-the-input-of-a-p2pkh-transaction

   Legacy input size: 148 bytes (compressed)

    Legacy output size: 34 bytes (compressed)

    Segwit input size: 104 bytes
    Segwit output size: 32 bytes

Outputs for P2PKH and P2SH are both the same size: 34 bytes

So let's take an example and calculate the size:
https://blockchain.info/tx/7e46a5ea9d9c19cd4d0c3d0a287419d7c1ae13049ac7ab8860b6ee0cec4ead17

We have 1 input
There 2 Output

So the transaction size ~= 13 * 148 + 2 * 34 + 10 ~= 226 Bytes

Check this link, you will learn more about it:
https://blog.rmcsoft.com/how-to-calculate-bitcoin-transaction-fee/

[DannyHamilton]

So for example we know that a transaction contains:

• a certain number of inputs
• a cetrain number of outputs

Correct.

• a locking scrpit (scriptPubKey)

No.

Not A locking script.

Each output has its own locking script to lock THAT output, so if you have multiple outputs then you have multiple locking scripts.

More importantly, EACH output IS two things: a locking script, and the amount of satoshis being locked.

That's it.  That's the entire output.

• an unlocking script (scriptSig)

No.

Not AN unlocking script.

Each input has its own unlocking script to unlock THAT input, so if you have multiple inputs then you have multiple unlocking scripts.

More importantly, EACH input IS three things: a reference to a previously unspent output, and the unlocking script that allows you to spend that previous output, a sequence number.

That's it.  That's the entire input.

... and other elements.

There are about 10 bytes of "other elements".

• A 4 byte version number
• 1 or more bytes indicating the quantity of inputs
• 1 or more bytes indicating the quantity of outputs
• A 4 byte locktime

Unless you have significantly more than a hundred inputs or significantly more than a hundred outputs, the number of inputs and outputs will not need more than 1 byte each.