How to measure a plant pot

Does your plant look a little too big for its pot? Are its leaves yellowing or hanging off to the side? Maybe you’re facing the opposite issue, and your plant looks like a tiny shrub amongst an oversized planter. Both of these things are equally troubling. 

It’s time to repot your plant, but how to measure for the right planter? Do it by eye, and you could end up returning your purchase when it turns out to be too small. Instead of guessing, we recommend measuring your current plant pot and sizing up. 

Here’s how to measure a plant pot, with detailed instructions on diameter, volume and width. We’ll also delve into the different types of plant pots and their purposes. Learn more with Whitaker's Garden Centre! 

What does plant size mean?

When we discuss ‘plant size’, it’s less a comment on the actual plant, but rather its container. 

The size of a pot is directly related to a plant’s health: it affects access to nutrients, can stunt or increase root growth and make sure it’s got plenty of room to grow (that is, if it’s the appropriate size). 

UK manufacturers tend to measure plant pots by volume (litres), which indicates the amount of soil the pot can hold. 

An example is the difference between a 2-litre and 20-litre pot: one is suitable for young shrubs or perennials, while the other is capable of holding larger specimens, such as small trees. 

If you want your plant to thrive, using a container that’s neither too big nor too small is key. Let’s learn more about the measurements you need to look out for (and how to measure a plant pot). 

Diameter/width

The diameter (or width) of a plant pot is the surface area it has to grow. Here’s how to measure it, depending on shape: 

• Circular: Measure across the top rim at its widest point. 
• Rectangular or square: Measure both the length and width across the top rim.

Height

For proper root development, your plant pot needs to be the right height. You can measure it accurately by placing a ruler or tape measure vertically alongside the pot. Start from the base and work your way up to the top rim.

Volume

As we mentioned earlier, ‘volume’ refers to the total amount of soil it can contain. Plant pots are usually sold (and priced) according to volume, so you shouldn’t have to work this out at home. 

However, if you’ve misplaced the information (or received the pot from a friend), here’s what you’d need to determine its volume: 

• Cylindrical: Calculate volume using the formula: π × (radius)² × height. For example, a pot with a radius of 10 cm and a height of 20 cm has a volume of approximately 6.28 litres.
• Rectangular: Use the formula: length × width × height. For instance, a pot measuring 30 cm in length, 20 cm in width, and 25 cm in height has a volume of 15 litres.

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

But what if you’re not even at the purchasing stage yet? If you’ve pressed pause on your plant pot journey because you’re confused about the different types, let us clear up the two main kinds: nursery and decorative. 

What are nursery pots? 

Called as such because they ‘nurse’ the plant’s growth, nursery pots provide the conditions for root establishment. 

They’re often made from plastic or other rigid materials that can maintain their shape, and most critically, they come with drainage holes to prevent overwatering. 

Nursery pots aren’t chosen for their ‘aesthetic appeal’: they’re more for functional purposes, so don’t expect to find many great designs! 

What are decorative pots? 

Here is where you get to have fun! Decorative pots don’t house the plants themselves, but act as containers for the nursery pots. 

When shopping, choose a pot that’s slightly larger than your nursery pot. Doing so will ensure that removing the plant for watering is easy, and the specimen does not become stuck or compressed. 

Why is plant pot size important? 

Root space and nutrients

Put simply, plants require the right amount of space and a proper soil-to-root ratio to thrive. 

A pot that is too small will stunt a plant because it lacks sufficient space and nutrients to grow. If the roots fill the container or are growing out of the drainage holes, this is another sign the plant needs a larger pot. 

Water management and root rot

An oversized planter can be just as harmful as one that is too small. When there is too much soil for the root mass, the plant could struggle to collect nutrients. 

Larger containers also collect more water, which can lead to excessive moisture and create a breeding ground for pests and root rot. 

Does my planter need holes for drainage?

100%, every plant pot needs drainage holes. Why? Because every plant needs water! 

But not too much! Without adequate drainage, there's a risk of overwatering your plant. When there's too much soil for a plant's root mass, the container holds more moisture than the roots can absorb. 

Signs of this include your plants struggling, withering, or even emitting an odour. That’s why it’s essential to select suitable pots. 

Size guide for measuring a plant pot 

Below, we’ve put together a size guide for nursery pots and decorative pots. 

Shop for plants and plant pots with Whitaker's Garden Centre! 

If you’re ready to take the next step in plant care, there’s no time like the present! 

Getting your plant the help it needs (a larger or smaller pot) will all but ensure its growth. Remember to follow its care instructions (e.g., likes shady conditions, water infrequently), and it won’t be long before your plant is back to blooming! 

While you’re here, why not explore our range of pots and planters? Whitaker's Garden Centre offers gardeners a range of nursery pots and decorative pots, with essential terracotta planters and decorative planter cans.

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