Contract multiplier

取引乗数。株式オプション1枚は100株を対象とするため、プレミアム2.00ドルなら費用は200ドルとなる。提示価格には必ず100を掛ける。

The contract multiplier tells you how many shares one option contract actually controls. For standard US equity options that number is 100, so the price you see quoted is per share, not per contract. When a call shows a premium of 2.50, you pay 2.50 times 100, or 250 dollars, to buy one contract.

This matters most when you size a position. If you want exposure to roughly 300 shares of a stock, you buy three contracts, because each one already represents 100 shares. The multiplier also drives your profit and loss: a strike that finishes 3.00 in the money is worth 300 dollars per contract at expiration, not 3.

The common mistake is forgetting the multiplier and treating the quoted premium as the full cost. Also watch out for adjusted contracts after a split, spin-off or special dividend, where the deliverable and effective multiplier can change and no longer match the neat 100 shares you expect.

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