A US listed equity option controls 100 shares. That 100 is so universal it stops being a number you think about — it is baked into every mental shortcut about premium, notional and exposure.
A crypto option typically controls one coin. Some venues use fractions of a coin for higher-priced assets. Neither is 100.
Where it goes wrong
Notional. The exposure of one contract is roughly the coin price, not a hundred times it. A book with a given contract count is a hundredth of the notional an equity trader’s instinct suggests.
Dollar gamma. Any dealer map multiplies open interest by gamma and by a multiplier. Use 100 on a chain where the multiplier is 1 and every figure — net GEX, wall size, the flip’s sensitivity — is a hundred times too large. The shape of the map survives; the magnitudes are fiction, which is worse than an obvious error because the picture still looks right.
Comparing books. Comparing crypto open interest against equity open interest by contract count compares two different units. It has to be converted to notional first, and then converted correctly.
The other specs worth checking
Strike increments are coarser relative to price than on a liquid equity, which affects how precisely a wall can sit. Minimum tick sizes are quoted in the settlement currency. And the settlement type — coin or stablecoin — changes the payoff shape, not just the currency of the payout.
The habit that prevents it
Read the contract specification once per venue and per product, and write down the multiplier before computing anything. It is a thirty-second check that protects every downstream number, and it is the sort of error that survives review precisely because nobody re-derives a constant they think they know.