The size of a transaction (in bytes) is determined by the number of inputs and the number of outputs.
Every transaction has 10 bytes of required information.
Each output adds another 34 bytes
Each input adds 148 bytes if it was previously received at a compressed key address and 180 bytes if it was received at an uncompressed key address.
Looking at your other post...
This transaction is the one you said you created:
3b16f704f1086d2f3bcfe1716618027045092ab52fec85013ebc2999d50d9174It has only
1 input of 0.01 bitcoins that were previously received at address 1xExA3dry8eavsAMrtAzZd1KWMk78BiHB (a compressed key address) at 2017-02-23 03:40:00 UTC in transaction b54c0dd3b91bf0137b2d7900d4a0216d9b193bea5125d59188ae6364bd3dca78.
It has only
1 output of 0.00981107 bitcoins sent to address 13Q3jM8fwznuV5WGCRJSwTGFzdjVYE8NnN
The remaining
0.00018893 bitcoins is the transaction fee.
The size of your transaction is:
10 bytes + 34 bytes (one output) + 148 bytes (one compressed key input) =
192 bytes.
The fee you paid is:
0.00018893 bitcoins / 192bytes =
0.00000098 bitcoins per byte
This is one of your friend's transaction:
4126ada7e11d40ea8ba77743571d2ae5562ab41033cce7e253b7e255405a96eaIt has only
1 input of 0.20833 bitcoins that were previously received at address 13Q3jM8fwznuV5WGCRJSwTGFzdjVYE8NnN (an uncompressed key address) at 2017-02-15 15:37:51 UTC in transaction 0fcf2b850d898a55d9264d43c06b8d2c3ab4d6269e97d66cf616deb539dcdcab.
It has
2 outputs- One output is 0.2 bitcoins sent to 1JmnkuZNXm72v1h2yRY11uNd2UcR27x7LH
- The other output is 0.0081831 bitcoins sent back to address 13Q3jM8fwznuV5WGCRJSwTGFzdjVYE8NnN
The remaining
0.00014690 bitcoins is the transaction fee.
The size of your friend's transaction is:
10 bytes + 68 bytes (two outputs) + 180 bytes (one uncompressed key input) =
258 bytes.
The fee your friend paid is:
0.00014690 bitcoins / 258 bytes =
0.00000057 bitcoins per byteYour transaction confirmed faster because you paid a transaction fee that is
0.00000041 bitcoins MORE per byte than your friend.
This is another of your friend's transaction:
1fdaf7e2f50aea9d272165232f578bc62c3875abdd06b2b4bd2e1eb63bf40088It has only
1 input of 0.06057447 bitcoins that were previously received at address 13Q3jM8fwznuV5WGCRJSwTGFzdjVYE8NnN (an uncompressed key address) at 2017-02-13 08:25:40 UTC in transaction 66f35a46101d441840beef33df0eb1b36bfa61df5f38651235405dae03738387.
It has
2 outputs- One output is 0.02223 bitcoins sent to 1Aq8nBwVLzXTJvoAt1z11gvbXFMW2i9C7P
- The other output is 0.03818447 bitcoins sent back to address 13Q3jM8fwznuV5WGCRJSwTGFzdjVYE8NnN
The remaining
0.00016 bitcoins is the transaction fee.
The size of your friend's transaction is:
10 bytes + 68 bytes (two outputs) + 180 bytes (one uncompressed key input) =
258 bytes.
The fee your friend paid is:
0.00016 bitcoins / 258 bytes =
0.00000062 bitcoins per byteYour transaction confirmed faster because you paid a transaction fee that is
0.00000036 bitcoins MORE per byte than your friend.