Put/call ratio
Put volume divided by call volume, or put open interest divided by call open interest, for a symbol or set of contracts over a period.
A ratio above 1 means more puts than calls traded, and a ratio below 1 means more calls than puts. The ratio is computed per underlying, per expiration or across a group of symbols, and it can use volume, open interest or premium.
A rising ratio can reflect bearish bets, but it also rises when holders of stock buy puts as protection, so it measures relative activity and leaves the motive open. Index options tend to carry higher put/call ratios than single stocks because of hedging demand.
Illustrative example (hypothetical numbers, not a real trade): in one session a stock’s options trade 18,000 puts and 24,000 calls. The volume put/call ratio is 18,000 ÷ 24,000 = 0.75, meaning three puts traded for every four calls.