Transaction size WTF???

[MakFrogz]

Hi guys!

Look, we can calculate transaction size approximately by using formula in*148 + out*34 +10 +/- in.

Okey, i took one transaction from explorer with 4 inputs, 2 outputs and size was 1,392 bytes.


Calculate size manual:

4*148 + 2*34 + 10 +/- 4 = 670 +/-4

Can someone explain to me whyyy?

[1714026296]

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[NeuroticFish]

You should start with providing the transaction Id, maybe somebody can help on real data.
Afaik the simple rule is OK for legacy transaction; SegWit, especially from 3* addresses, are bigger.

Some other/older clues can be in this thread (which I didn't actually read) https://bitcointalk.org/index.php?topic=1291540.0

[o_e_l_e_o]

The numbers you have quoted are only accurate for P2PKH outputs and P2PKH inputs. All other outputs and inputs have different values. For the majority of these, such as standard P2SH or bech32 SegWit, the size will be smaller, but there are some P2SH addresses (notably multisig) with much larger sizes, up to several hundred bytes per input.

Link to the transaction you are analyzing and perhaps we can help further.

[MakFrogz]

Transaction id: 346a4733f64874102f6cc18c552d9e6862947a59ea02815b2fb434e450714bdd

[NeuroticFish]

Transaction id: 346a4733f64874102f6cc18c552d9e6862947a59ea02815b2fb434e450714bdd

I think that's testnet "legacy compatible segwit".
Also for SegWit the number of bytes doesn't matter that much, the calculation goes by vBytes.

I don't know a simple formula, however, this is what I've found for you:
https://bitcoin.stackexchange.com/questions/87275/how-to-calculate-segwit-transaction-fee-in-bytes
https://gist.github.com/junderw/b43af3253ea5865ed52cb51c200ac19c
https://www.reddit.com/r/Bitcoin/comments/7m8ald/how_do_i_calculate_my_fees_for_a_transaction_sent/  (read the comments)

[bitmover]

Transaction id: 346a4733f64874102f6cc18c552d9e6862947a59ea02815b2fb434e450714bdd

I think that's testnet "legacy compatible segwit".

That's really testnet. Why don't you try on the mainnet,?

https://live.blockcypher.com/btc-testnet/tx/346a4733f64874102f6cc18c552d9e6862947a59ea02815b2fb434e450714bdd/

I think 1300 bytes is a lot to. Something may be different because of testnet?. I simulated here https://www.buybitcoinworldwide.com/fee-calculator/ and the total was 600 for legacy and 450 for segwit.

[MakFrogz]

One more example
Size: 1,360 bytes, 4 inputs and one output.

Code:

{
  "status" : "success",
  "data" : {
    "network" : "BTCTEST",
    "txid" : "09da6cd256e7281623bfc7697195c5dbe7b802ad7b3d9d1316046228be5910da",
    "blockhash" : "00000000000002199acefe80fb48a8291b41ea77f60a7ce9f993e4562ca44116",
    "block_no" : 1517813,
    "confirmations" : 1,
    "time" : 1558447791,
    "version" : 1,
    "locktime" : 0,
    "sent_value" : "0.00800000",
    "fee" : "0.00185554",
    "inputs" : [
      {
        "input_no" : 0,
        "address" : "2MvUtaocsd8oAxxghimgG2Zwqwz8iN53uUv",
        "value" : "0.00200000",
        "received_from" : {
          "txid" : "f3a7b4da9739bc80427ff0e33ad2054a1206b5e4413abe48bd478543c01f164a",
          "output_no" : 8
        },
        "script_asm" : "0020cb113b7b27e04afad667e0d5e4b329f41b22bda3a7e6d8678a7452f4c8b5bb6c",
        "script_hex" : "220020cb113b7b27e04afad667e0d5e4b329f41b22bda3a7e6d8678a7452f4c8b5bb6c",
        "witness" : [
          "",
          "30450221009788300c030726aa5fd6119f0de387a53b571dfe50421d1601295360722ebec5022028b8b9a61a521e4fbf38051a1ceb13ed48d062e7c337f87cdcb61a44c3ac68b901",
          "30450221009aa556ea53b6d934adb2f0b962c6e3bb31064a7236fcc03af1e16c26c96e72230220114717521b6fafb6dc1f271b2551ed3bc61a1f3768e33d8d16891607fdd12bff01",
          "52210231f0ba0b4a867e1e3d995ec508b03db52cce50ea1bfc31fb10101633b410b50d210328f8d004c408e43110468760ac44a3a6a7f6737da7e05a0e62893ae4ea7ce5d32103cc7cff5ffb6e147ee97e5e5a383ceefc26f6de6e6d2de52d5384070de7c0e15c53ae"
        ]
      },
      {
        "input_no" : 1,
        "address" : "2MvUtaocsd8oAxxghimgG2Zwqwz8iN53uUv",
        "value" : "0.00200000",
        "received_from" : {
          "txid" : "f3a7b4da9739bc80427ff0e33ad2054a1206b5e4413abe48bd478543c01f164a",
          "output_no" : 19
        },
        "script_asm" : "0020cb113b7b27e04afad667e0d5e4b329f41b22bda3a7e6d8678a7452f4c8b5bb6c",
        "script_hex" : "220020cb113b7b27e04afad667e0d5e4b329f41b22bda3a7e6d8678a7452f4c8b5bb6c",
        "witness" : [
          "",
          "304402202b730b52539c2da05ac9c440cfffa8a6c4546643b69fa6e969f05c4eae81134a0220554f8e0bd690e693771a2345f5d39380a184f303470a7ae097bfa965a4b6cdd901",
          "304402207d8ca23361b513b8f3e32005a1b81c70c49b49a166887ac86301e3098c0d3e0d02203ac116ef4455dfb7700a8498fd0e345b0084bd36be7734e062db7631388f690101",
          "52210231f0ba0b4a867e1e3d995ec508b03db52cce50ea1bfc31fb10101633b410b50d210328f8d004c408e43110468760ac44a3a6a7f6737da7e05a0e62893ae4ea7ce5d32103cc7cff5ffb6e147ee97e5e5a383ceefc26f6de6e6d2de52d5384070de7c0e15c53ae"
        ]
      },
      {
        "input_no" : 2,
        "address" : "2MvUtaocsd8oAxxghimgG2Zwqwz8iN53uUv",
        "value" : "0.00200000",
        "received_from" : {
          "txid" : "f3a7b4da9739bc80427ff0e33ad2054a1206b5e4413abe48bd478543c01f164a",
          "output_no" : 42
        },
        "script_asm" : "0020cb113b7b27e04afad667e0d5e4b329f41b22bda3a7e6d8678a7452f4c8b5bb6c",
        "script_hex" : "220020cb113b7b27e04afad667e0d5e4b329f41b22bda3a7e6d8678a7452f4c8b5bb6c",
        "witness" : [
          "",
          "304402207b9f36e5fab0713f968de835bbfb44eb157402e79561b9ecd86409ab1c914d8b02206efa6f5b0fcff27cf8a71c40bb448d33b61022c47d5b374b5f5723b197d456e401",
          "3044022057d48b41e19ea228136585d2e0e0f12011759549c97388b0e3392bd073f65c340220582aa800624b4000f64fdf3f9ba8b9c43f41388e68604fb6154f3ccc85d88c9801",
          "52210231f0ba0b4a867e1e3d995ec508b03db52cce50ea1bfc31fb10101633b410b50d210328f8d004c408e43110468760ac44a3a6a7f6737da7e05a0e62893ae4ea7ce5d32103cc7cff5ffb6e147ee97e5e5a383ceefc26f6de6e6d2de52d5384070de7c0e15c53ae"
        ]
      },
      {
        "input_no" : 3,
        "address" : "2MvUtaocsd8oAxxghimgG2Zwqwz8iN53uUv",
        "value" : "0.00200000",
        "received_from" : {
          "txid" : "f3a7b4da9739bc80427ff0e33ad2054a1206b5e4413abe48bd478543c01f164a",
          "output_no" : 70
        },
        "script_asm" : "0020cb113b7b27e04afad667e0d5e4b329f41b22bda3a7e6d8678a7452f4c8b5bb6c",
        "script_hex" : "220020cb113b7b27e04afad667e0d5e4b329f41b22bda3a7e6d8678a7452f4c8b5bb6c",
        "witness" : [
          "",
          "30450221009356066a417e04036b3116297758914169ad1f451dc6765a9a05851e540e05e002207947f5a3d61fdba58b3b7ee456e2fa089ee12ac2517565a8f206377728eb23bc01",
          "3045022100da5fee3f655c7747341c997526a35fd1fd1e9a6b8cfacc942eedbc294e4e90580220756534f9f2c991cf1c4dc544989e1854015045cd204af1e0e9090d9919d730ea01",
          "52210231f0ba0b4a867e1e3d995ec508b03db52cce50ea1bfc31fb10101633b410b50d210328f8d004c408e43110468760ac44a3a6a7f6737da7e05a0e62893ae4ea7ce5d32103cc7cff5ffb6e147ee97e5e5a383ceefc26f6de6e6d2de52d5384070de7c0e15c53ae"
        ]
      }
    ],
    "outputs" : [
      {
        "output_no" : 0,
        "address" : "2MuNttpkNFcbUcfQw5mwxqsoh4ehnWWHkdz",
        "value" : "0.00614446",
        "type" : "scripthash",
        "req_sigs" : 1,
        "spent" : {
          "txid" : "52b3e898712ca5dfa65044d4cdd74eeab17e86355731dcdc5f4046cd95c7cac3",
          "input_no" : 0
        },
        "script_asm" : "OP_HASH160 1763a3e95e08bacc415ec85442b1efca5a1294a4 OP_EQUAL",
        "script_hex" : "a9141763a3e95e08bacc415ec85442b1efca5a1294a487"
      }
    ],
    "tx_hex" : "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"
  },
  "code" : 200,
  "message" : ""
}

[HCP]

Again, this is using SegWit inputs... and your "calculation" is only valid for P2PKH inputs/outputs.

So while the raw "hex" size might be 1360 bytes... it would appear that it's calculated "virtual size" is only "346 bytes":

Code: (https://api.blockcypher.com/v1/btc/test3/txs/09da6cd256e7281623bfc7697195c5dbe7b802ad7b3d9d1316046228be5910da?limit=50&includeHex=true)

{
  "block_hash": "00000000000002199acefe80fb48a8291b41ea77f60a7ce9f993e4562ca44116",
...
  "size": 346,
...
}

"vsize" = Transaction weight / 4
"weight" = 3 times the stripped_size in bytes (excluding the witness) plus the total_size in bytes (including the witness)

I suggest you go and read these:
https://bitcoin.stackexchange.com/questions/87275/how-to-calculate-segwit-transaction-fee-in-bytes
https://bitcoincore.org/en/segwit_wallet_dev/#transaction-fee-estimation