Bid size and ask size

Bid size and ask size show how many shares are available at the best current bid and ask prices for a stock. Bid size is the number of shares buyers are currently willing to purchase at the highest posted bid price, and ask size is the number of shares sellers are willing to sell at the lowest posted ask price. Depending on the data source, both numbers are shown either as share counts or in round lots, and they update constantly as orders arrive and get filled or canceled.

These figures give a quick read on the depth of interest at the top of the order book, separate from the price itself. A stock quoted at a bid of $50.00 with a bid size of 200 shares has far less buying support waiting at that price than one with a bid size of 20,000 shares. A trader placing a large order can use bid size and ask size to gauge how much of the order is likely to fill immediately at the quoted price before the market has to move to find more sellers or buyers.

Thin bid and ask sizes are common in less liquid stocks and can make prices move sharply on relatively small orders, since there is not much size standing between the current quote and the next price level. Heavily traded large-cap stocks typically show much larger bid and ask sizes, letting sizable orders fill without moving the price much. Traders watching level 2 quotes can see bid size and ask size not just at the top of the book but at multiple price levels behind it.