What is VOUT?

In every Bitcoin transaction, multiple outputs can be created. To distinguish between them when spending later, Bitcoin uses a simple indexing system called VOUT (Virtual Output).

1. The Zero-Based Index

Bitcoin uses zero-based indexing.

• The first output in a transaction is VOUT 0.

• The second output is VOUT 1.

• The third is VOUT 2, and so on.

2. Why VOUT is Necessary

A TXID identifies a specific transaction, but that transaction might contain many different payments (outputs).

• Example: Alice sends 1 BTC to Bob and 0.5 BTC back to herself as change.

• Bob's output might be VOUT 0.

• Alice's change might be VOUT 1. If Bob wants to spend his 1 BTC later, he must tell the network: "I am spending the output from TXID [X] at VOUT 0."

3. The "OutPoint" Relationship

As we saw in the OutPoint Guide, the TXID and VOUT together form a unique coordinate.

• TXID: "Which transaction created the coins?"

• VOUT: "Which specific slot in that transaction contains the coins?"

4. Visualizing VOUTs

Imagine a transaction with three outputs:

Transaction [Hash A]
  Output 0 (VOUT 0): 1.2 BTC -> Address X
  Output 1 (VOUT 1): 0.5 BTC -> Address Y
  Output 2 (VOUT 2): 0.1 BTC -> Address Z

In the next section, we will look at the Data Type and physical limits of the VOUT field.