Blockchain.info new feature or what?

[lady Royal]

Hi,

Today I sent payment from my online wallet and I noticed that they have added one new feature in which we can set fees according to satoshis/byte format.
I want to know how Blockchain.info is detecting the size of the transaction?
It's not the predicted fee when I sent the transaction, it exactly showed the fee I have put before sending the transaction.
Really want to know how they measure the fee before sending the transaction.

Regards

[brobbel]

Hi,

Today I sent payment from my online wallet and I noticed that they have added one new feature in which we can set fees according to satoshis/byte format.
I want to know how Blockchain.info is detecting the size of the transaction?
It's not the predicted fee when I sent the transaction, it exactly showed the fee I have put before sending the transaction.
Really want to know how they measure the fee before sending the transaction.

Regards

The size of a transaction depends on the number of inputs and the number of outputs (and some other stuff), so when you want to pay from your blockchain.info wallet it knows exactly how big this transaction will be.

[lady Royal]

Hi,

Today I sent payment from my online wallet and I noticed that they have added one new feature in which we can set fees according to satoshis/byte format.
I want to know how Blockchain.info is detecting the size of the transaction?
It's not the predicted fee when I sent the transaction, it exactly showed the fee I have put before sending the transaction.
Really want to know how they measure the fee before sending the transaction.

Regards

The size of a transaction depends on the number of inputs and the number of outputs (and some other stuff), so when you want to pay from your blockchain.info wallet it knows exactly how big this transaction will be.

No, What I have seen here on the forum and heard from everyone that the size of Bitcoin transaction cannot be predicted. You can only know the size of the transaction only if the transaction is processed, then how can you identify it before?

[brobbel]

No, What I have seen here on the forum and heard from everyone that the size of Bitcoin transaction cannot be predicted. You can only know the size of the transaction only if the transaction is processed, then how can you identify it before?

I'm sorry, but that's wrong.

Assuming all the inputs you are spending are from regular "pay to address" transactions, each input will contribute 180 (plus or minus 1) bytes to the transaction. Each output adds 34 bytes to the transaction. And there's a fixed extra 10 bytes which are always present.

The "plus or minus 1" comes from the fact that each input needs a signature to be claimed. The signature contains two 32 byte values, but if either of the values has a first byte of 0x80 or more, it has a 0x00 byte prepended to it. So I'm assuming one of the two is high and the other is low. That way I'm off by at most one byte per input.

So 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.

If the inputs are from "pay to pubkey" transactions then the inputs are smaller than for "pay to address" transactions. And this will be different also for "pay to script hash" inputs too, depending on how/if that's implemented.

Edit: This transaction was made with bitcoins stolen in the Linode heist and shows a transaction size of 1337, possibly a deliberate use of leetspeak in the blockchain.

Edit2: Now that compressed public keys are commonplace, each input is 32 bytes shorter and so the transaction size is now:

in*148 + out*34 + 10 plus or minus 'in'

So it is predictable.

[lady Royal]

It is not, I have read the above quote, I agree with it someone did a really great search. Can you post the link to it?
Sometimes, We have very large transaction size, even the transaction has only one input and one output, So, how can you explain that?

[brobbel]

It is not, I have read the above quote, I agree with it someone did a really great search. Can you post the link to it?
Sometimes, We have very large transaction size, even the transaction has only one input and one output, So, how can you explain that?

I shall quote the bitcointalk post with links to above quote. The first link is the link I quoted.

Assuming all the inputs you are spending are from regular "pay to address" transactions, each input will contribute 180 (plus or minus 1) bytes to the transaction. Each output adds 34 bytes to the transaction. And there's a fixed extra 10 bytes which are always present.

The "plus or minus 1" comes from the fact that each input needs a signature to be claimed. The signature contains two 32 byte values, but if either of the values has a first byte of 0x80 or more, it has a 0x00 byte prepended to it. So I'm assuming one of the two is high and the other is low. That way I'm off by at most one byte per input.

So 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'

Recommended fee is 0.0001BTC/1000 bytes. All popular wallets calculate fees automatically.

Read

• http://bitcoin.stackexchange.com/questions/1195/how-to-calculate-transaction-size-before-sending
• http://bitcoin.stackexchange.com/questions/7537/calculator-for-estimated-tx-fees

[HCP]

It is not, I have read the above quote, I agree with it someone did a really great search. Can you post the link to it?
Sometimes, We have very large transaction size, even the transaction has only one input and one output, So, how can you explain that?

Then you are misunderstanding either the terms, or what is counted as an input or an output.

An input is NOT an address... so if you see something like this:


Which looks like 1 input... but has a MASSIVE transaction size... click the "Show scripts & coinbase" link... then you'll see the ACTUAL inputs to the transaction... like this:



Check this transaction for an example: https://blockchain.info/tx/271f6489c2d5562046be3965dd2d1a2f7bf6f200d967c0c70dfef6cfb987eb12

Every single one of those inputs adds at least 148 bytes to the transaction. This is why you shouldn't collect dust inputs to your wallet... if you're collecting faucets or doing captcha's or cloud mining or whatever... set your MINIMUM payout to at least 0.001 if not 0.01... otherwise you are generating dust inputs which end up costing you a lot to include in a transaction... each input = 148 bytes... recommended fees of 300+ sats/byte = 148 * 300 = 44,400 sats to include an input in a transaction... if your input was only 100,000 sats to start with, you need to spend 44% of it just to put it in the transaction!!?!

[lady Royal]

It is not, I have read the above quote, I agree with it someone did a really great search. Can you post the link to it?
Sometimes, We have very large transaction size, even the transaction has only one input and one output, So, how can you explain that?

Then you are misunderstanding either the terms, or what is counted as an input or an output.

An input is NOT an address... so if you see something like this:


Which looks like 1 input... but has a MASSIVE transaction size... click the "Show scripts & coinbase" link... then you'll see the ACTUAL inputs to the transaction... like this:



Check this transaction for an example: https://blockchain.info/tx/271f6489c2d5562046be3965dd2d1a2f7bf6f200d967c0c70dfef6cfb987eb12

Every single one of those inputs adds at least 148 bytes to the transaction. This is why you shouldn't collect dust inputs to your wallet... if you're collecting faucets or doing captcha's or cloud mining or whatever... set your MINIMUM payout to at least 0.001 if not 0.01... otherwise you are generating dust inputs which end up costing you a lot to include in a transaction... each input = 148 bytes... recommended fees of 300+ sats/byte = 148 * 300 = 44,400 sats to include an input in a transaction... if your input was only 100,000 sats to start with, you need to spend 44% of it just to put it in the transaction!!?!

Thanks for your replies guys, So, It means it's predictable. I will post again if I find something. I already know about the script and bases option by Blockchain.info that it shows the number of outputs and inputs.
Thanks again.