These high quality, economical plastic Petri dishes are perfect for classrooms or science fair projects. Grow bacteria, sprout seeds, hold small items for viewing, observe life in pond water, etc. The sterile plastic dishes have a consistently even surface and excellent optical clarity. They feature a triple-vented lid to help prevent condensation, and are easily stackable. Sold in packs of 20 dishes. Large dishes: 10 cm dia. Small dishes: 5.5 cm dia. Mini dishes: 3.5 cm dia.