Bitcoin Forum

Steam require at least one confirmation when you buy using Bitcoin , my transaction took too long and when I checked blockchain.info I saw that there is no new blocks (It took sometime) then I noticed something else which is the "Total sent" and "Size (Kb)" columns.

So here is the thing , sometimes the Size doesn't even reach 1mb but the amounts in "Total sent" is higher then the blocks where there is a lower amount of BTC sent , so I'm really wondering how is the size calculated ? I'm pretty sure It has nothing to do with how much BTC is sent or received.

To the question "how is it calculated?", the answer is "clearly, quite poorly". This is Blokchain.info, they've made a USP out of this sort of mistake for a while now.

General answer is: inputs. How many inputs are you using for your transaction, the more those mount up, the larger the overall transaction will be on the blockchain.

It mostly depends on the number of inputs and outputs.  I say mostly because even a couple of extra symbols can make a transaction larger, so if a more advanced user inserted a custom script inside a transaction it will increase the size too.  It actually makes perfect sense because everything have size in the internet.

use google my friend, you can find all you need to know about everything there so much faster than asking it here and possibly get some false replies in the middle of it too:

the first reply here is answering you well:
https://bitcoin.stackexchange.com/questions/1195/how-to-calculate-transaction-size-before-sending