are round lots more common than odd lots 
round lots are among the most common large trading orders as they incur the lowest trading fees but odd lots are becoming more common among traders and brokers that s because automated and electronic trading makes it easier to execute these trades at lower costs the bottom linea lot is the total number of units of a financial instrument that is bought and sold on an exchange lots can be mixed odd or round the size of a round lot is determined by the exchange in most cases it is made up of 100 shares of a financial security such as a stock or bond it may also be a multiple of 100 trading round lots helps improve market efficiency and because it s a bulk order also provides traders with lower trading costs 