A unit pack (lot) of shares the size of which varies according to the price of a share. It is a standard trading quantity (e.g., 500 or 1000 shares) for a particular security. On exchanges, trading takes place in multiples of the board lot. The cost of trading in board lots is usually lower than for trading in quantities less than a board lot (such quantities are referred to as odd lots).

In the United States, a board lot, which is more commonly known as a round lot, is 100 shares on all the stock exchanges. For thinly traded stocks, it consists of 10 shares. In countries where exchanges list a high number of of low-priced stocks, board lots are often larger or set at levels proportionate to price ranges.