A typical circulated 1951 Australian half penny is worth approximately $0.20 AUD—essentially its face value equivalent in decimal currency.
Coins in uncirculated condition (graded MS60 and above) can fetch $10 AUD to $50+ AUD, depending on grade, luster, and eye appeal. Higher grades (MS65+) command premium prices.
For an accurate valuation, have the coin assessed by a professional numismatist or refer to current Australian coin catalogues (e.g., Renniks, Downies) and recent auction results.