Definition of Ask size:
The total number of shares offered for sale at the current quote. Ask size is typically quoted in units of 100, where an ask size of three equals 300 shares offered. An ask size of 300 equals 30,000 shares offered. See Ask; Best Ask. Compare to Bid Size.
The ask size is the amount of a security that a market maker is offering to sell at the ask price. The higher the ask size, the more supply there is that people want to sell. When a buyer seeks to purchase a security, he or she can accept the ask price and buy up to the ask size amount at that price. If the buyer wishes to acquire more of the security over the current ask size, he or she may have to pay a slightly higher price to the next available seller.
Market makers are the ones who offer to buy and sell securities. The market maker must state the price it is asking for a given security (the ask price) and the amount it is willing to sell at that price (the ask size). Also, the market maker must state the price at which it is willing to buy the security (the bid price) and the amount of securities it is willing to buy (the bid size). When a customer order comes to the exchange, the order is filled by the market marker with the lowest ask price (for buy orders) or the highest bid price (for sell orders).
Meaning of Ask size & Ask size Definition