An order to buy or sell a security (stock, bond, etc.) in a standard amount- i.e., a multiple of the standard amount per order (standard order unit). For example, the standard order unit for stocks is 100 shares or its multiples for an order. Therefore, an order to buy or sell 500 shares is an even lot (in which 100 constitutes a standard lot). For bonds, the standard lot is five bonds.

An order that involves non-standard order units will be tackled and filled as an odd lot (uneven lot or broken lot). For example, an order to buy or sell 75 shares is an odd lot. Likewise, an order to trade 125 shares involves both an even lot of 100 shares and an odd lot of 25 shares.

Even lot is also known as round lot.