Pot Size Calculator
Plant type to recommended pot diameter, depth, gallon size, and soil volume.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Using the right pot size is one of the most overlooked factors in container gardening. A pot that is too small restricts roots, dries out too quickly, and limits the plant's yield and size. A pot that is too large holds excess moisture that can lead to root rot. Here is how to use this calculator:
- Select your plant type. Each plant type has a recommended diameter, depth, and container volume based on its root structure and mature size. Shallow-rooted plants like lettuce and herbs need less depth than deep-rooted crops like tomatoes and peppers.
- Read your results. The calculator shows the recommended diameter, depth, gallon size, and approximate soil volume needed to fill the pot. The notes section gives variety-specific tips that can help you get better results.
- Apply to your situation. These are starting-point recommendations. If you live in a very hot climate, go one size larger to retain more moisture. If you are limited on space or are growing a compact variety, the lower end of the range is fine.
The soil volume estimate is based on a cylinder of the recommended diameter and depth, which gives a useful approximation even for round, tapered, or square pots of equivalent volume.
About the Pot Size Calculator
Pot sizes are typically described in gallons in the United States. Container volume in gallons corresponds roughly to diameter: a 1-gallon pot is about 6-7 inches across, a 5-gallon is 12-14 inches, and a 15-gallon is 18-22 inches. These are approximations because pot shapes vary. When in doubt, match the depth recommendation first, then the diameter, as root depth matters more than volume for most vegetables.
Glazed ceramic and plastic pots retain moisture longer than terracotta, which is porous and evaporates water through its walls. In hot, dry climates, plastic or glazed pots reduce watering frequency. In humid or cool climates, terracotta's breathability helps prevent overwatering. Dark-colored pots absorb heat and can raise soil temperature by 10-15°F, which can stress roots in summer. All calculations run entirely in your browser with no data stored or transmitted.
Frequently Asked Questions
What size pot do I need for tomatoes?
Tomatoes need at least a 5-gallon container (approximately 12 inches in diameter and 12 inches deep) for compact or determinate varieties. Indeterminate varieties that keep growing all season perform best in 10-15 gallon containers (14-18 inches diameter). Larger containers hold more soil, retain moisture better between waterings, and provide the root volume that large plants need to support heavy fruit loads. In very hot climates, using a 15-20 gallon container can dramatically reduce watering frequency and heat stress.
How do I know if my plant needs a larger pot?
Signs that a plant is pot-bound and needs repotting include roots growing out of the drainage holes, roots circling visibly on the soil surface, soil drying out very quickly after watering (within a day or two), stunted growth despite adequate fertilization, and the plant wilting frequently even when watered regularly. When repotting, go up one pot size (2-4 inches larger in diameter), not more. Moving to a dramatically larger pot adds unnecessary soil volume that stays wet too long and can cause root rot.
Can I grow succulents in a large pot?
It is not recommended. Succulents have small, shallow root systems and prefer pots that fit their root ball snugly with only about an inch of extra space on each side. In an oversized pot, the excess soil around the roots retains moisture far longer than succulents tolerate, leading to root rot even with careful watering. Use a pot just 1-2 inches larger than the plant's root ball, ensure it has drainage holes, and use a fast-draining cactus and succulent mix rather than regular potting soil.
Do I need drainage holes in a pot?
Yes, for almost every plant. Drainage holes allow excess water to escape rather than accumulating at the bottom of the pot, where it creates an anaerobic environment that promotes root rot. The common advice to add a layer of gravel at the bottom of pots without drainage holes does not solve this problem and can actually make it worse by raising the water table within the pot. The only reliable solution is a pot with holes. If you love a decorative pot without holes, use it as a cachepot: put your plant in a plastic nursery pot with holes inside the decorative outer pot, and remove the inner pot to water it.