the bid ask spread is the difference or spread between ? asking for a stock or a security and ? buyer is willing to pay. it is also simply referred to as bid ask or sell spread and is measured the same way. for example, jane wants to sell shares of stock in wonko gadgets. the price bid for the stocks is $4.50 per share. jane, however is asking $5.00 per share. the difference of $0.50 per share is called the bid ask spread. during the course of a normal trading day, there can be several bid prices and several ask prices on a stock or a security. yet only ? is used to calculate the bid ask spread. simply put, the bid ask spread is a negotiation in progress occurring over stocks and securities. securities with the lowest bid ask spread are those considered the most liquid or easily converted into cash assets. currency is considered the most liquid of securities traded and therefore usually as the lowest bid ask spread. this standard is often used as a measure of liquidity for any stock or security.