What Size Is A Standard Seed Tray? & What Does 1020 Mean?

If you are looking for seed trays to germinate seeds for your garden, you have probably seen the phrase “standard size” or “1020”.  You might be wondering what these phrases mean, and how to interpret the language.

I was wondering the same thing, so I did some research to figure out the differences.  Here’s what I learned.

So, what size is a standard seed tray?  A standard size (1020) seed tray is slightly larger than 10 inches long by 20 inches wide.  For example, a standard size seed tray might be 11 inches long by 21 inches wide, with a depth of 2 to 2.5 inches.  Sometimes, seed trays have separate compartments (cells) for each seed or group of seeds.  This makes it easier to separate the seedlings for transplanting later.

Of course, there are many sizes of seed trays available, so a standard 1020 seed tray is not your only option.  There are 1010 seed trays, and also seed trays that will hold round pots, instead of having square cells.  Let’s take a closer look at seed trays, their dimensions, and the options available.

What Size Is A Standard Seed Tray (What Does 1020 Mean)?

As mentioned above, a standard size seed tray (also called a “1020” tray) is slightly larger than 10 inches by 20 inches (25 centimeters by 51 centimeters), with a depth of 2 to 2.5 inches (5.1 to 6.4 centimeters).

seed tray
A standard seed tray has a length slightly more than 10 inches, and a width slightly more than 20 inches.

The phrase “1020” refers to the tray length and width, which are approximately 10 inches and 20 inches.

Often, a standard seed tray will measure a little bit more in both length and width.  For example, these seed trays from Johnny’s Selected Seeds measure 11 inches (28 centimeters) long by 21 inches (53 centimeters) wide.

As you can see, the seed trays from Johnny’s Selected seeds come as one large tray, with no individual compartments (cells) to separate the seeds.  This is a great option for growing microgreens, which will be harvested by cutting off the tops (rather than being transplanted at a later date).

On the other hand, these 1020 seed trays from the Bootstrap Farmer have separate cells for individual plants.  This makes it much easier to space out seeds properly, and allows you to transplant without harming the roots of your plants (since the roots of separate plants will not get tangled up together due to separated cells).

There are 50 separate cells in this seed tray (5 cells long by 10 cells wide).  The cell dimensions for this seed tray are 1.75 inches by 1.75 inches (4.45 centimeters by 4.45 centimeters), with a height of 2.25 inches (5.72 centimeters).

Each cell has a 0.25 inch (0.64 centimeter) drainage hole, which also helps to remove the seedling and soil when it is time to transplant outdoors for spring planting.

You can even place the entire seed tray in a corresponding 1020 seed tray (without compartments).  Then, you can water the seedlings from below by adding water to the bottom tray.

That way, you won’t have to worry about overwatering any one cell and killing your seedlings before they have a chance to grow.

What Other Seed Tray Sizes Are Available?

There are lots of other options if you decide to buy a seed tray with different dimensions.  Let’s explore a few of them here.

1010 Seed Tray

A 1010 seed tray has dimensions slightly larger than 10 inches by 10 inches (25.4 centimeters by 25.4 centimeters).  These trays are square, and are often compatible with 1020 trays so that you can put two 1010 seed trays side by side to fit a 1020 seed tray.

These 1010 seed trays from the Bootstrap Farmer also have drainage holes to prevent overwatering or to allow watering from a reservoir below the tray.

seed tray
A 1010 seed tray is slightly more than 10 inches long and 10 inches wide.

The tray dimensions are 10.5 inches long by 10.5 inches wide by 2.5 inches deep (26.7 centimeters long by 26.7 centimeters wide by 6.4 centimeters deep).

1020 Net Pot Tray

If you want to grow plants in separate round pots for either hydroponics or traditional soil gardening, then the 1020 Net Pot Tray is a good option.

tomato seedling
A 1020 net pot tray will hold 32 2-inch round pots – a good option if you want to give your seedlings more room and time to grow indoors.

Instead of square cells, these trays have circular holes to hold individual round pots.  These pots are larger than the standard square cells, allowing you to give seedlings more room and more time for growth indoors, which helps to offset late spring frosts or a short growing season.

This 1020 Net Pot Tray from the Bootstrap Farmer fits 32 2-inch round pots (4 pots long by 8 pots wide), spaced about 0.5 inches apart.

These net pot trays fit perfectly into a standard 1020 tray, which allows for watering from below (if using traditional soil gardening) or a hydroponic setup.

6 Cell (2×3) Plug Tray Inserts

These smaller 6 cell trays from Bootstrap Farmer are perfect if you want to keep different plants in separate trays, but grow them in the same place.

Each cell in the tray is 1.5 inches by 1.5 inches (3.8 centimeters by 3.8 centimeters) at the top, tapering down to 1 inch by 1 inch (2.5 centimeters by 2.5 centimeters) at the bottom.  The height is 2.25 inches (5.7 centimeters).

The inserts are designed so that 12 of them will fit in a standard 1020 tray, allowing for watering from below.

Humidity Domes

A humidity dome is a plastic cover used to trap moisture in a small area so that seeds can germinate better.  Humidity domes are sized to fit the corresponding seed tray size.

For example, this 1020 humidity dome from the Bootstrap Farmer will fit over a standard 1020 seed tray.

Humidity domes are helpful because they make it easier to maintain high humidity levels in soil for germinating seeds.  They can also keep seeds or seedlings warmer by producing a “greenhouse effect” if you have a grow light setup above your seed trays.

For more information, check out my article on humidity domes.

One word of caution is necessary.  Be careful about mixing and matching trays and humidity domes.

If you buy equipment from different companies, there can be slight differences in dimensions.  Sometimes, these differences mean that a dome or insert will not quite fit a tray.

Another (Non-Tray) Indoor Growing Option

There is another option for growing indoors, which is a little bit different from the seed trays we have discussed so far: grow bags.

A grow bag is made of durable canvas material, and is used to hold soil and plants.  A grow bag can be used to grow either one large plant or multiple smaller plants.

Larger grow bags can even be used to hold dwarf fruit trees, or to get larger fruit trees started indoors.

Grow bags can be used indoors or outdoors, or even planted directly in the ground.  Grow bags prevent plants from becoming “root-bound” as they do in standard plastic or clay containers.

They are reusable, and can last for years if given proper cleaning and care.  For more information, check out my article on why to use grow bags.

How Many Seeds Should You Put In Each Cell In A Seed Tray?

I would suggest planting two seeds per cell in a seed tray.  That way, there is a very high chance that at least one seed in each cell will germinate.  This means that you won’t have many, if any, empty cells.

However, in order to avoid competition between plants, it is a good idea to “thin” the seedlings by removing any extra ones.  If two seedlings start to grow in one cell, wait for a few days and observe them.  Then, leave the stronger one to grow and pull out the weaker one.

radish seedlings
When multiple seedlings sprout in one cell, it is better to leave the strongest one and remove the others.

It seems cruel, and it can be difficult for gardeners to do this!  However, if you don’t thin the seedlings, then the roots of the two seedlings will become intertwined.

This makes it difficult to separate them out for transplanting later.  Even worse, the two seedlings will compete for resources (water and soil nutrients).

Ultimately, this will lead to two plants that are both smaller and weaker than one dominant plant would have been.  So, make sure to thin your seedlings when the time comes!

What Happens If You Plant Seeds Too Close Together?

If you plant seeds too close together, you will see overcrowding & competition in your seed trays.  The roots of separate plants will become tangled together, making it difficult to separate them out later.

This makes it much more likely that the roots of some plants will be damaged during transplant.  In turn, this will cause more of your plants to wither and die when exposed to the harsher conditions outdoors when you try to harden them off in the spring.

You can avoid this problem if you use seed trays with separate cells, as long as you thin the seedlings when two or more grow in a cell.

If your seed tray does not have separate cells, then you will need to make sure that you use proper spacing for the seeds.  Check online or look at the seed packet to find the recommended seed spacing for the plants you are growing.


By now, you know what size a standard seed tray is, and you know what the cryptic phrase “1020” refers to.  You also know about some of the other options available for seed tray dimensions.

I hope you found this article helpful – if so, please share it with someone who can use the information.  If you have any questions about seed tray sizes, please leave a comment below.


Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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