Which is better for reading gamma levels on ES, SPX or SPY?

SPX is the closer match in underlying and participants, but its chain requires a data source that carries index options. SPY-derived levels are a proxy: useful when stated as such, less precise because the ETF-to-futures conversion adds error and SPY positioning is a different book.

Why is an SPX option about ten times more expensive than a SPY option?

Both use a multiplier of 100, but the index is roughly ten times the ETF price, so a comparable strike and expiry controls about ten times the notional. The premium, gamma and delta exposure per contract scale accordingly.

SPX vs SPY options

SPX options are written on the S&P 500 index itself, are European-style and cash-settled, and control about ten times the notional of a SPY option. SPY options are written on the SPDR S&P 500 ETF, are American-style and physically settled in shares. Both track the same market, but their positioning, settlement and levels are not interchangeable.

Senzoukria · Glossary · Updated September 2026

At a glance

SPX: Index options, multiplier 100, European, cash-settled
SPY: ETF options, 100 shares, American, physically settled
Scale: SPY trades near one tenth of the index level

Side-by-side

Contract terms that change the reading of a level
Aspect	SPX options	SPY options
Underlying	S&P 500 index	SPDR S&P 500 ETF
Multiplier	100 dollars × index	100 shares
Notional per contract at index 5,000	About 500,000 dollars	About 50,000 dollars
Exercise style	European	American
Settlement	Cash (monthly AM on SET, SPXW PM on close)	Delivery of ETF shares
Dividends	Index level excludes them; reflected through the forward	The ETF pays them; relevant to early exercise of calls
Trading hours	Regular session plus curb and global trading hours sessions	US options regular session

Two books, not one

The participants differ. SPX concentrates institutional hedging and large index strategies, SPY attracts a broader mix including retail and share-based strategies. Open interest and flow in one product are not a scaled copy of the other, so gamma exposure computed on SPY can place walls and a zero crossing at strikes that do not correspond to the SPX ones divided by ten. The ratio between SPY and the index itself also drifts slightly over time, because of the ETF's dividends and fees.

Mapping to ES futures

A level computed on either product must be moved onto the futures price scale. From SPX, the futures basis is added; from SPY, the ETF price must first be scaled to the index or directly to the futures price. Example: with SPY at 500 and ES at 5,040, a ratio of 10.08 turns a SPY call wall at 505 into about 5,090 on the ES chart. The ratio changes as the basis moves, so a mapped level is best read as a zone.

In Senzoukria

The GEX overlay on futures charts maps ES and MES to SPY, NQ and MNQ to QQQ, RTY and M2K to IWM, and YM and MYM to DIA, because the default options source does not serve SPX or NDX cash chains; the ETF proxy is stated rather than hidden. The ratio is the chart's last close divided by the ETF spot, fixed until the next snapshot so the levels do not follow price tick by tick, and every converted level carries the source ticker in its label, for example a call wall tagged SPY on an ES chart.

In the same section

Sources

Cboe — S&P 500 index options product specifications (2026-09-25)

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Frequently asked questions

Which is better for reading gamma levels on ES, SPX or SPY?: SPX is the closer match in underlying and participants, but its chain requires a data source that carries index options. SPY-derived levels are a proxy: useful when stated as such, less precise because the ETF-to-futures conversion adds error and SPY positioning is a different book.
Why is an SPX option about ten times more expensive than a SPY option?: Both use a multiplier of 100, but the index is roughly ten times the ETF price, so a comparable strike and expiry controls about ten times the notional. The premium, gamma and delta exposure per contract scale accordingly.

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