The amount field in a transaction output specifies how many satoshis (the smallest unit of bitcoin) are being assigned to this output.

Let's examine our transaction to understand this better:

Amount Field Structure

• Size: 8 bytes (64 bits)
• Format: Little-endian integer
• Unit: Satoshis (1 BTC = 100,000,000 satoshis)
• Range: 0 to 21,000,000 * 100,000,000 satoshis (maximum bitcoin supply)

Implementation Example

Here's how you might parse a transaction output's amount:

def parse_amount(raw_tx: bytes, offset: int = 0) -> tuple[int, int]:
    """
    Parse an amount from raw transaction bytes
    
    Args:
        raw_tx: Raw transaction bytes
        offset: Starting position in bytes
        
    Returns:
        (amount, new_offset)
    """
    # Read 8 bytes for amount
    amount_bytes = raw_tx[offset:offset + 8]
    
    # Convert to integer (little-endian)
    amount = int.from_bytes(amount_bytes, 'little')
    
    return amount, offset + 8

Amount Validation Rules

When validating transaction amounts, nodes must ensure:

1. Non-negative: All output amounts must be ≥ 0 satoshis
2. Input sum ≥ Output sum: The sum of all input amounts must be greater than or equal to the sum of all output amounts
3. Maximum supply: No single output can exceed the maximum bitcoin supply (21 million BTC)

Unit Conversion

Here's a helpful function for converting between BTC and satoshis:

def btc_to_satoshis(btc: float) -> int:
    """Convert BTC amount to satoshis"""
    return int(btc * 100_000_000)

def satoshis_to_btc(sats: int) -> float:
"""Convert satoshi amount to BTC"""
return sats / 100_000_000

Common conversions:

• 1 BTC = 100,000,000 satoshis
• 0.00000001 BTC = 1 satoshi
• 0.001 BTC = 100,000 satoshis