The total number of securities that are offered for sale at the current quote in a given market. Differently stated, it is the number of round lots available on the sell side of the market.

A typical ask size is quoted in multiples of 100 (a round lot represents 100 securities). Therefore, an ask size of 4 equals 400 securities offered for sale in a given market. An ask size of 100 equals 10,000 securities offered for sale, and so on. Ask sizes are an important indicator of the supply and liquidity of a security at a given time.

The ask size and its counterpart, the bid size, are key for determination of the possibility to set up a profitable trade.