Plant Pot Size Guide: P9, Litres, Diameter, and Common Pot Types

Plant pot sizing becomes confusing when nursery labels, litre sizes, diameter measurements, and retail planter formats all get mixed together. A clear size guide should make those systems easier to compare, not add more buying noise.

This guide stays focused on one job: helping you read pot sizes correctly, compare common nursery labels, and understand which kinds of pot formats people usually mean when they shop by size.

Start with the Two Main Sizing Systems

Most pot sizing starts from either diameter or capacity.

Diameter sizing

How diameter is usually read

Diameter sizing usually refers to the width across the top opening.

Smaller nursery pots are often described by diameter or trade labels like P9.

Litre sizing

How capacity is usually read

Litre sizing usually refers to approximate soil volume.

Larger nursery stock is more often labelled in litres, such as 2L, 5L, or 10L.

A practical rule: diameter tells you how wide the pot is at the top. Litres tell you how much growing volume the pot roughly holds. Good pot-size decisions usually need both.

What P9, 1L, 2L, 5L, and 10L Usually Mean

Trade labels are only useful if they help you picture the real size of the pot. The guide below is meant for comparison, not for exact manufacturing specifications.

Lineup of common nursery pot sizes including P9, 1L, 2L, 5L, and 10L for size comparison

Use trade-size labels to shortlist, then confirm exact dimensions if fit is important.
Common label	Typical top diameter	Usually used for	What it usually means in practice
P9	About 9 cm / 3.5 in	Starter herbs, young perennials, smaller nursery stock	Entry-level nursery size, often bought for growing on rather than instant impact
1 litre	About 13 cm / 5 in	Small houseplants, herbs, younger shrubs	Still compact, but more rooted and easier to display or pot up
2 to 3 litres	About 17 to 19 cm / 6.5 to 7.5 in	Shrubs, climbers, perennials with more first-year impact	Often the most practical everyday nursery size for planting out
4 to 5 litres	About 22 to 24 cm / 9 to 9.5 in	Larger shrubs, roses, patio plants, stronger root systems	Bigger root room and more visible impact, but also more weight and carrying cost
10 to 15 litres	About 28 to 32 cm / 11 to 12.5 in	Specimen shrubs, trees, larger statement plants	A more established plant size, often bought for quicker landscape effect
20 litres and up	Usually 35 cm+ / 14 in+	Mature shrubs, feature planting, larger commercial or designer projects	Less about a casual pot-up, more about immediate visual scale and weighty handling

How to Measure a Pot Properly

If you only measure one dimension, use the inside top width for nursery-size comparison. If fit matters, measure more than the rim.

Size charts help you shortlist. Exact fit usually needs a fuller dimension check.

Top diameter

Measure across the inner top opening from one side to the other. This is the most common reference point for nursery pots and trade sizes.

Height

Check height separately when root depth, shelf clearance, sleeve fit, or shipping carton size matters.

Base diameter

Two pots with the same top width can taper differently. Base width matters when pots sit in trays, racks, sleeves, or inserts.

Stated litres

Use litre size as a practical comparison point, but do not assume two 5L pots will share the same proportions.

When exact fit matters

Confirm top diameter, base diameter, height, and stated capacity together. That is the quickest way to avoid surprises when the pot needs to fit a tray, shelf, sleeve, decorative cover pot, or shipping box.

Repotting: What the Next Size Usually Looks Like

A size guide should help with the next move, not just define labels. For most plants, the safest step is still a moderate size-up rather than a dramatic jump.

Most plants are easier to manage when you size up gradually rather than jumping several pot sizes at once.
Current pot	Usually safer next step	Why
P9 / 9 cm	About 13 cm / 1 litre	Gives extra root room without surrounding a small plant with too much wet unused soil
13 cm / 1 litre	About 17 cm / 2 litres	A practical next step for many foliage plants, herbs, and younger ornamentals
17 to 19 cm / 2 to 3 litres	About 22 to 24 cm / 4 to 5 litres	Works when the plant is clearly ready for more root room and more stable growing volume
22 cm+ pots	Size-up decisions become more plant-specific	At larger sizes, root behaviour, weight, handling, and final placement matter more than a simple chart rule

Minimum Pot Sizes for Herbs and Vegetables

Edibles are one of the fastest ways to make pot size feel practical. The goal here is not the perfect final container for every climate. It is a useful minimum baseline.

Use these as working minimums for one plant per container unless noted otherwise.
Minimum diameter	Often suitable for	Main note
10 in	Small herbs, strawberry	Good for smaller-rooted edible planting and lighter seasonal use
14 in	Most herbs, spinach, lettuce, arugula, compact leafy crops	A practical middle ground for mixed edible container use
18 in	Broccoli, cauliflower, larger cabbage, small pepper, determinate tomato	Needs more volume and steadier watering than smaller herb containers
24 in	Large peppers, indeterminate tomato, cucumber, artichoke, larger mixed planting	Used when stronger root room and higher water demand become harder to ignore

Comparison of plant pots with the same litre size

Why Two Pots with the Same Litre Label Can Still Look Different

Litre labels help with broad comparison, but they do not lock every pot into one exact shape. Brands vary in taper, wall thickness, height, and how wide the pot opens at the top.

A taller pot may hold similar volume with a smaller footprint.
A wider pot may look larger at first glance even when litre size is similar.
A thicker-walled decorative pot may have less growing room inside than the outer dimensions suggest.

Useful shortcut: use litre size to compare growing volume, and use diameter plus height when appearance or fit is the real question.

Common Decorative Pot Types You Will See in Retail

Plant pot size guides often become more useful when they also acknowledge the formats people actually shop. The same 30 cm diameter does not mean the same thing if the product is a round floor pot, a window box, a hanging planter, or a wall planter.

Format changes how size should be read. The same diameter can behave very differently across product types.

Round floor plant pot used for straightforward diameter and height comparison

Round floor pots

Usually the easiest size comparison. Diameter and height are both easy to read, which makes them the most literal format for general size shopping.

Window box planter showing why length matters alongside width and volume

Window boxes and troughs

Length becomes just as important as diameter or volume. These are often judged by sill, ledge, or railing fit rather than litre size alone.

Wall planter or flat-back planter fitted against a wall or sill

Wall planters and flat-back planters

Chosen more by fit against a wall, sill, or fence than by nursery-style volume labels. Projection from the wall matters as much as planting space.

Hanging planters

Filled weight matters quickly. Diameter is only one part of the decision once soil volume and suspension load come into play.

Railing planter mounted on a balcony or fence rail showing bracket fit

Railing planters and fitted planters

Hook width, bracket fit, base shape, and outer profile can matter more than stated litres. These are the formats where full dimensions often matter most.

When Size Charts Help — and When They Do Not

Use size charts to shortlist. Stop using them as the only decision tool when shape, shelf fit, tray fit, or shipping dimensions matter.

Best use

When charts are strongest

Charts are strongest when you are comparing nursery stock, common litres, and repotting steps.

Limit

When charts are weaker

Charts are weaker when decorative planters vary a lot in height, taper, wall thickness, or outer profile.

What matters next

When product specs matter more

Product specifications matter more whenever fit is tight or the planter format is unusual.

FAQ

How is plant pot size usually measured?

Plant pot size is usually measured either by top diameter or by capacity in litres. Smaller nursery pots are often referred to by diameter, while larger nursery stock is often labelled by litre size.

What does a P9 pot mean?

A P9 pot usually means a nursery pot with a top diameter of about 9 cm. It is commonly used for younger plants, starter herbs, and small perennials.

Should I always move a plant into a much larger pot?

Usually no. For many plants, moving up one practical size at a time is safer than jumping several sizes at once.

Why do two pots with the same litre label sometimes look different?

Manufacturers vary in height, taper, wall thickness, and shape. A litre label is useful for comparison, but exact dimensions still matter when fit is important.

What is the difference between a nursery pot size and a decorative planter size?

Nursery pot sizes usually help describe the plant stock itself. Decorative planters are more likely to vary by shape, outer dimensions, and intended use such as floor pots, window boxes, or wall planters.