A portable cooler stacking system is provided, where portable coolers of different shapes and sizes can be optimally and stably stacked. The cooler system can include a first cooler having a first size and a second cooler having a second size, where the first and second sizes are different. A pair of second coolers can be stacked on the first cooler, where the second coolers are positioned widthwise along the length of the lid of the first cooler. In this manner, an inner length of the top surface of the lid of the first cooler is slightly greater then the width of a lower portion the second coolers and the inner width of the top surface of the lid of the first cooler is greater then two times the width of the lower portion of the second coolers. As such, two second cooler can be positioned widthwise along the length of the lid of the first cooler. The adjacent position of the second coolers and the interlocking surfaces substantially limit the horizontal movement of the pair of second coolers on the lid of the first cooler.