Why is SPX notional about ten times SPY notional per contract?

Both have a multiplier of 100, but SPY trades at roughly one tenth of the S&P 500 index level. One SPX contract therefore controls about ten times the dollar exposure of one SPY contract at comparable strikes.

Does the multiplier affect implied volatility or greeks per share?

No. Implied volatility and per-unit greeks are computed from the quoted price. The multiplier only scales them into contract-level and dollar exposures, which is where mistakes usually occur.

Option contract multiplier

The contract multiplier converts an option's quoted price into dollars and defines how much underlying one contract controls: 100 shares for standard US equity and ETF options, 100 dollars per index point for SPX, and one futures contract for options on futures. Premium, delta exposure and gamma exposure all scale with it.

Senzoukria · Glossary · Updated September 2026

At a glance

US equity and ETF options: 100 shares per contract
SPX index options: 100 dollars × index level
E-mini S&P 500 futures options: One ES future, 50 dollars per index point

What the multiplier does

Option prices are quoted per unit of underlying: per share, per index point or per futures point. The multiplier turns that quote into the amount paid for one contract and into the quantity of underlying the contract represents. It is part of the contract specification, set by the exchange, and it is not the same across products that track the same index.

Worked examples

Delta exposure scales the same way: an SPX option with delta 0.5 at an index level of 5,000 represents 0.5 × 100 × 5,000 = 250,000 dollars of index exposure, the same as one E-mini future.

One contract at a quoted price
Product	Quote	Multiplier	Premium per contract
SPY option	2.35	100 shares	235 dollars
SPX option	23.50	100 dollars per point	2,350 dollars
E-mini S&P 500 option	20.00 points	50 dollars per point	1,000 dollars
Micro E-mini S&P 500 option	20.00 points	5 dollars per point	100 dollars

Adjusted contracts

After a split, a special dividend or a merger, existing options on a stock or ETF can be adjusted so that one contract delivers a non-standard package, for example a different number of shares or shares plus cash. Such series keep trading beside the standard ones and can carry large open interest. A calculation that assumes 100 shares for every contract misstates their premium and exposure, so aggregation tools should either handle the deliverable or exclude adjusted series.

In Senzoukria

Option Flow computes the premium of each print as price × size × 100, the standard equity and ETF multiplier.
The GEX module scales every leg with a multiplier of 100: GEX = OI × gamma × 100 × spot² × 0.01 per 1% move, and delta, vega, theta, vanna and charm exposures use the same 100. The app applies this constant to every leg; it does not model non-standard deliverables of adjusted contracts.
Comparing an ETF-based total with an index-based total requires accounting for the price scale as well as the multiplier: an SPX contract controls roughly ten times the value of a SPY contract.

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Frequently asked questions

Why is SPX notional about ten times SPY notional per contract?: Both have a multiplier of 100, but SPY trades at roughly one tenth of the S&P 500 index level. One SPX contract therefore controls about ten times the dollar exposure of one SPY contract at comparable strikes.
Does the multiplier affect implied volatility or greeks per share?: No. Implied volatility and per-unit greeks are computed from the quoted price. The multiplier only scales them into contract-level and dollar exposures, which is where mistakes usually occur.

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