A Petri dish is a shallow, transparent, cylindrical container used in biology laboratories. It provides a sterile, controlled environment for culturing microorganisms like bacteria and fungi, or for growing isolated cells. Scientists use the dish to observe culture growth and behavior over time without external contamination. Dimensions are standardized to ensure reproducibility across different experiments and laboratories.
The Most Common Standard Dimensions
The most widely adopted size for general microbiological work is the 90-millimeter (mm) Petri dish. This diameter is considered the global benchmark for routine culturing and diagnostics. The standard height is around 15 mm, providing sufficient space for the growth medium (usually agar) while remaining shallow for easy observation and stacking.
This 90 mm size offers an optimal balance between surface area and the amount of growth media required, making it efficient for general lab use. A slightly larger version, the 100 mm dish, is also frequently referred to as a standard size, particularly in mammalian cell culture applications.
The 100 mm dish often comes with a slightly taller profile, around 20 mm in height. This greater volume capacity is useful for cell lines that require more culture media to support longer-term growth or higher cell densities. Both the 90 mm and 100 mm sizes are designed for compatibility with common laboratory incubators, shakers, and automated handling systems.
Range of Sizes and Specialized Dishes
Petri dishes are available across a spectrum of sizes, ranging from small “mini” dishes to very large formats, each designed for specific experimental needs. At the smaller end, 35 mm and 60 mm diameter dishes are common for small-scale experiments where sample volume is limited. These smaller dishes conserve media and biological samples, and they are easier to handle under a microscope for direct observation.
Conversely, large-scale studies often require dishes measuring 150 mm in diameter. This size provides a significantly larger surface area, necessary for high-volume culturing, large-scale viral research, or testing multiple experimental treatments side-by-side. The increased capacity also supports more extended growth periods before the culture media dries out.
Beyond the circular shape, specialized dishes exist to accommodate complex protocols. Segmented or divided dishes contain internal walls that separate the plate into two or more distinct compartments, allowing researchers to compare different samples or conditions while preventing cross-contamination. Square-shaped dishes are also available, useful in certain automated systems or when working with plant tissue culture. Many modern plastic dishes incorporate features like stacking rings or ridges on the lid and base. These features allow for stable, non-slipping stacks and ensure a stable air gap for gas exchange during incubation.
Factors Driving Size Selection
The size of the Petri dish selected for an experiment is determined by several practical laboratory considerations.
Key Selection Factors
- The required volume of the growth media, as larger dishes need more agar or liquid media to cover the increased surface area adequately.
- The scale of the experiment; small dishes are preferred for high-throughput screening, while bulk production requires the maximum surface area provided by 150 mm dishes.
- The specific type of cell being cultured, as adherent cells require more flat surface area to attach and grow compared to suspended cells.
- Compatibility with existing laboratory equipment, such as robotic arms for automated liquid handling or specialized racks within high-capacity incubators.
Researchers select a dish size that minimizes media waste while still providing enough nutrients for the culture to thrive.