Transaction Weight
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# Transaction Weight A metric for measuring the "size" of a transaction.

With the introduction of BIP 141 (Segregated Witness), transactions were given a new unit of measurement called weight.

This weight measurement basically gives the validation part of a transaction (the signature data) a discount, so it doesn't take up as much "space" inside a block. In other words, the signature data is less costly than the rest of the transaction data.

## Calculation

The weight of a transaction is calculated by multiplying the size (in bytes) of different parts of the transaction data by different values:

Data Multiplier
Version x4
Marker x1
Flag x1
Input Count x4
Input x4
Output Count x4
Output x4
Witness x1
Locktime x4

### Example

Transaction: `c586389e5e4b3acb9d6c8be1c19ae8ab2795397633176f5a6442a261bbdefc3a`

`0200000000010140d43a99926d43eb0e619bf0b3d83b4a31f60c176beecfb9d35bf45e54d0f7420100000017160014a4b4ca48de0b3fffc15404a1acdc8dbaae226955ffffffff0100e1f5050000000017a9144a1154d50b03292b3024370901711946cb7cccc387024830450221008604ef8f6d8afa892dee0f31259b6ce02dd70c545cfcfed8148179971876c54a022076d771d6e91bed212783c9b06e0de600fab2d518fad6f15a2b191d7fbd262a3e0121039d25ab79f41f75ceaf882411fd41fa670a4c672c23ffaf0e361a969cde0692e800000000`
Data Bytes Multiplier Weight
Non-Witness 106 x4 434
Witness 110 x1 110
534

## FAQ

### Why x4?

The factor of 4 helps to create more of a balance between the the cost of creating an output and the cost of spending an output.

In typical transaction data, an output can be created using around 32 bytes, but spending it requires around 108 bytes:

However, by using the new weight metric, there is more of an even balance between the cost of creating an output and spending an output:

As a result, this creates a more balanced incentive to spend outputs, which should help to reduce the size of the UTXO set (which takes up valuable space in RAM on a computer running a full node).

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