Bid size is a fundamental measure of market liquidity. It refers to the quantity of a security that investors are willing to buy at the specified bid price. The bid size is always stated in board lots, which represents a unit of 100 shares. As such, a bid size of four would translate to 400 shares. An understanding of the bid size and maintaining real-time track of it is highly crucial as it offers insights into the availability and level of liquidity of the security in question.

The bid sizes at the best available bid prices are all reflected in the Level 1 quotation. This indicates how many smaller investors are bidding (or offering) buy/sell orders, and how interested they are in disposing of their shares in the market.

The Level 2 quotation, on the other hand, offers investors the opportunity to get more in-depth information on market demand. It provides details on the quantity and price of many bids and offers. This information helps investors to make more informed decisions while trading. It also serves as an important tool in determining the entry and exit points in a security.

Apart from investors, traders and brokers can use the bid size to gauge the sentiment of the market. A larger bid size indicates that more traders are interested in the security. An increasing bid size also might serve as a signal for investors to follow the market trend. investors then would assess the bid size along with other financial indicators to make the decision of whether to buy or sell.

In conclusion, bid size is an important tool for investors and traders as it aids in decision making and offers a gauge for market sentiment.