What Is a Petri Dish? Types & Uses

Last verified: October 6, 2026. A Petri dish (also called a Petri plate or culture dish) is a shallow, flat, round, transparent dish with a loosely fitting lid, used in laboratories to grow microorganisms, cultivate cells, or hold small samples. It is typically filled with a layer of nutrient medium, most commonly a gel such as agar, and then inoculated with the material to be grown. It is among the most recognizable pieces of laboratory equipment in the world, and a mainstay of microbiology, cell biology, and teaching labs.

The problem a Petri dish solves is how to grow and observe living material in a controlled, visible, and contained way. A wide, shallow surface lets individual microbes spread out and grow into separate, visible colonies. A clear lid lets the culture be seen and photographed without opening it, while keeping contaminants out, and the stackable shape makes it easy to store and incubate many at once.

How a Petri Dish Works

A Petri dish has two halves: a shallow base that holds the contents and a slightly larger lid that sits over it. The lid is not airtight; it leaves a small gap that allows some gas exchange while still blocking most airborne contaminants and dust. In a typical microbiology workflow:

Medium is prepared and poured. A nutrient solution containing a gelling agent such as agar is sterilized, usually in an autoclave, allowed to cool somewhat, and poured into the dish, where it sets into a solid layer.
The sample is added. A small amount of material is spread, streaked, or dropped onto the surface using a sterile loop, spreader, or pipette. Streaking is a common method of thinning the sample so single cells end up separated from each other.
The dish is incubated. Dishes are often placed lid-side down, so condensation collects on the lid instead of dripping onto the culture. They are held at a temperature suited to the organism being grown, in an incubator.
Growth is observed. Each visible spot of growth, or colony, generally arises from a single cell or small clump of cells, and its appearance, along with how it grows on different media, helps researchers describe and identify what is growing.

What Goes Inside: Media in General

The dish is only the vessel; what makes a culture useful is the medium inside it. Some media are general-purpose and support the growth of many kinds of organisms. Others are selective, containing ingredients that encourage some organisms while suppressing others, and some are differential, producing visible changes such as color shifts that help tell organisms apart. Researchers choose the medium to match the question being asked, and the same dish can hold very different media. Labs often buy plates pre-poured, or pour their own from prepared powders, depending on volume and quality-control needs.

Who Uses Petri Dishes, and Why

Petri dishes are used across the life sciences and in many other settings:

Microbiology — growing, isolating, counting, and identifying bacteria and fungi, and testing how organisms respond to antimicrobial substances.
Cell biology — culturing adherent mammalian and other cells on specially treated surfaces, for experiments and for imaging.
Plant science — germinating seeds or growing small plant tissues on sterile media.
Clinical and diagnostic laboratories — culturing samples to detect and identify organisms.
Food, water, and environmental testing — checking for and counting microorganisms in samples.
Teaching — classroom demonstrations of microbial growth, since the results are visible without a microscope.
General holding and handling — many labs also use dishes simply to hold small objects, tissue pieces, or small organisms for observation or dissection.

Types of Petri Dishes

Dishes differ in material, size, and surface, and the right choice depends on the work:

Plastic (disposable) dishes — usually polystyrene, supplied sterile and discarded after use. They are by far the most common choice today because they are convenient and remove the need for cleaning and re-sterilizing.
Glass dishes — reusable and able to withstand heat sterilization, but they must be cleaned and sterilized between uses and can break. Some labs still prefer glass for specific work. For how different glassware compares, see types of laboratory glassware.
Tissue-culture-treated dishes — plastic dishes with a surface treated so that cells can attach and grow, used for cell culture rather than for growing microbes on agar.
Size variations — from small dishes that hold a few milliliters to large ones for bigger cultures, along with dishes divided into sections, so that more than one medium can be held in the same dish.
Specialty dishes — dishes with grids that help with counting colonies, dishes with a glass bottom for high-resolution microscopy, and dishes with vented lids that give more airflow.

Disposable dishes are generally not meant to go through an autoclave for reuse, because many common plastics deform with heat. See which plastics are autoclavable for how this differs from one plastic to another.

How a Petri Dish Differs From Adjacent Equipment

Culture flask — a closed vessel, often with a neck and cap, used to grow larger volumes of cells or microbes in liquid. A Petri dish is open-faced and shallow, which suits solid media and observation.
Test tube or culture tube — used for liquid cultures and small-scale growth, where a Petri dish is used when a surface and visibility are needed.
Microplate — a plate with many small wells, designed for running many small cultures or assays in parallel, rather than one large surface.
Bioreactor — a controlled vessel for growing cells or microbes at larger scale with monitoring and control of conditions. See what a bioreactor is.
Watch glass or evaporating dish — chemistry glassware with a similar shape but built for other tasks, such as holding or evaporating chemicals, not for sterile culture.

Practical Notes for Research-Administration and Lab-Management Readers

Biosafety. Anything grown in a Petri dish is a culture, and the organism determines the containment and handling rules. Cultures should be handled according to the institution’s biosafety program, with the work done at an appropriate level of containment. See biosafety levels BSL-1 to BSL-4 for how those levels are framed. Dishes should not be opened outside of approved procedures, and sealing a dish with tape is a common way to reduce the chance of an accidental opening.
Waste. Used cultures are biological waste and are usually decontaminated before disposal, commonly by autoclaving, according to institutional procedure. Disposable plastic dishes generate a large volume of laboratory plastic waste, which is a growing sustainability consideration.
Sterility and quality. Pre-sterilized dishes are supplied in sealed sleeves. Compromised packaging, scratched surfaces, or dishes that were not stored properly may increase contamination risk, which is why lab managers pay attention to storage and lot handling. For how sterile and non-sterile supplies are distinguished when purchasing, see the sterile versus non-sterile purchasing guide.
Procurement. Choices include material, size, whether the surface is treated for cell culture, venting, and whether to buy dishes already poured with medium. The right choice should follow the actual work; a treated cell-culture dish is not a drop-in replacement for an untreated microbiology dish, or the other way around.
Storage and handling. Poured plates are generally stored in a cool place and used within a limited time, as they can dry out or become contaminated. Plates are often labeled on the base rather than the lid so that labels do not get separated from the culture.

This page is general information, not clinical or safety training. Follow your institution’s procedures and the manufacturer’s instructions for any equipment you use.

The Short Version

A Petri dish is a shallow, round, lidded dish used to grow microorganisms or cells, or to hold small samples, usually on a layer of agar or other medium. Disposable plastic is the norm, glass is reusable, and treated dishes are made for cell culture. Because it holds living cultures, it comes with biosafety, waste, and sterility responsibilities that matter just as much as the choice of dish. For more on selecting and managing equipment and supplies like this, see CASRAI’s broader laboratory equipment and instrumentation coverage.

Frequently Asked Questions

What is a Petri dish used for?

It is used to grow and observe microorganisms and cells on a layer of nutrient medium, to isolate and count microbial colonies, and to hold small samples for observation or handling.

Why is a Petri dish shallow and flat?

A broad, shallow surface lets individual cells spread apart and grow into separate, visible colonies, and lets the culture be viewed directly through the clear lid without opening it.

Why are Petri dishes usually incubated upside down?

Plates are often incubated with the lid side down so that condensation collects on the lid rather than dripping onto the culture and spreading the growth.

What is agar?

Agar is a gelling agent, derived from certain seaweeds, that is mixed with a nutrient solution to form a firm gel when it cools. It provides a solid surface on which microbes can grow, and most microbes do not break it down.

Can Petri dishes be reused?

Glass dishes can be cleaned, sterilized, and reused. Plastic dishes are generally single-use and are discarded after the culture has been decontaminated, according to institutional procedure.

What is the difference between a Petri dish and a tissue culture dish?

A tissue culture dish has a surface treated so mammalian and other cells can attach and grow. A standard microbiology Petri dish is untreated and is generally used for growing microorganisms on agar.