Aquarium Dimensions in the UK: Length, Width and Height Explained

Aquarium dimensions refer to the length, width and height of a fish tank, but understanding them properly is essential when choosing the right aquarium size.

In the UK, aquarium dimensions are typically measured in centimetres (cm) and litres, while many online guides use inches and gallons, which often leads to confusion, especially for beginners trying to compare tank sizes.

This guide is a complete aquarium dimensions chart and explanation, covering:

• standard aquarium sizes in the UK
• aquarium dimensions in cm, inches, litres and gallons
• how to calculate tank volume
• and how to choose the best aquarium size for your home

Whether you're looking for a small 60cm tank or a large aquarium setup, this guide will help you understand exactly what size you need. 

Quick Answer: What Are Aquarium Dimensions?

Aquarium dimensions are the length, width and height of a fish tank, usually written as:

Length × Width × Height (L × W × H)

These measurements define the actual size and shape of the aquarium, not just its volume.

In the UK, aquarium dimensions are typically measured in:

• centimetres (cm) for tank size
• litres (L) for water volume

While many international guides use:

• inches
• gallons

Key points to know:

• Aquarium dimensions matter more than litres alone
• The length and width (footprint) are usually more important than height
• Two tanks with the same litres can have very different dimensions and usability
• Always check actual tank dimensions, not just the advertised size or volume
• Aquarium size directly affects fish health, stability and maintenance

Quick Tip:
A larger footprint (length × width) usually provides better conditions for fish than a taller tank with the same volume.

Quick Navigation

• Quick answer: What are aquarium dimensions?
• What do aquarium dimensions mean?
• Standard aquarium sizes in the UK
• Aquarium size chart (cm, inches, litres, gallons)
• Aquarium dimensions by litres
• Aquarium dimensions by gallons
• Aquarium dimensions calculator
• Why width matters more than you think
• Aquarium weight: empty vs filled
• How to measure aquarium dimensions correctly
• Which aquarium size should you choose?
• How to choose the right aquarium based on your needs
• FAQ
• Conclusion

What Do Aquarium Dimensions Actually Mean?

Aquarium dimensions refer to the length, width and height of a fish tank, and they determine the tank’s size, shape and usable space for fish.

These three measurements are:

• Length (L): the longest side of the tank, providing horizontal swimming space
• Width (W) / Depth: the distance from front glass to back glass, also known as the tank’s footprint
• Height (H): the vertical distance from the base to the top of the aquarium

Aquarium tank dimensions are usually written as:

Length × Width × Height (L × W × H)

Why Aquarium Dimensions Matter More Than Litres

Two aquariums can have the same volume in litres but behave very differently in practice.

For example:

• A long, shallow aquarium provides more swimming space and better oxygen exchange
• A tall, narrow aquarium may limit movement and reduce usable space for many fish

This is why the footprint (length × width) is often more important than total litres.

A larger footprint:

• improves water stability
• increases surface area for oxygen exchange
• allows more natural fish behaviour

This is why tank shape matters just as much as total volume.

Standard Aquarium Dimensions in the UK (Size Chart)

Standard aquarium dimensions in the UK are usually based on tank length (cm) and total volume (litres), but they can also be compared using inches and gallons.

Below is a practical aquarium size chart showing the most common tank dimensions used in the UK:

These are the most common aquarium tank dimensions in cm, inches, litres and gallons, but exact measurements can vary slightly between brands and manufacturers.

Always check the actual aquarium dimensions, not just the advertised volume, as tank shape and footprint can make a significant difference in usability. 

Use this table as a starting point, then compare the tank’s shape, usable space and full setup weight before buying.

Aquarium Size Chart (cm, Inches, Litres & Gallons)

This aquarium size chart compares the most common tank dimensions using cm, inches, litres and gallons, making it easier to choose the right aquarium size for your setup.

This aquarium dimensions chart provides a quick overview, but actual aquarium tank dimensions can vary by width and height, even when the length is the same. 

How to Use This Aquarium Size Chart

• A 60cm tank is usually the best starting point for beginners
• A 90cm aquarium provides more flexibility for community fish
• A 120cm tank offers better stability and stocking options
• Larger aquariums (150cm+) are ideal for experienced setups

Always consider the full aquarium dimensions (length × width × height), not just the length. 

Aquarium Dimensions by Litres (UK Guide)

Many UK fishkeepers search for aquarium dimensions by litres, especially when comparing tank sizes for beginners, betta fish or community setups.

Below are the most common aquarium sizes in litres, along with typical dimensions and use cases:

10 Litre Tank Dimensions

• Approx size: ~25 × 20 × 20 cm
• Volume: ~10L (~2 gallons)
• Best for: shrimp, snails, nano setups

Not recommended for most fish due to low stability.

20 Litre Tank Dimensions

• Approx size: ~40 × 25 × 20 cm
• Volume: ~20L (~4 gallons)
• Best for: small nano aquariums, beginner experiments

Better suited to simple nano setups than fully stocked fish communities.

60 Litre Aquarium Dimensions

• Approx size: ~60 × 30 × 30 cm
• Volume: ~54–60L (~12–13 gallons)
• Best for: beginner fish tanks, small community fish

This is one of the most popular aquarium sizes in the UK.

120 Litre Aquarium Dimensions

• Approx size: ~100–120 cm length
• Volume: ~120L (~26 gallons)
• Best for: stable community aquariums

Provides more flexibility for stocking and aquascaping.

240 Litre Aquarium Dimensions

• Approx size: ~120 × 45 × 45 cm
• Volume: ~240L (~53 gallons)
• Best for: advanced setups, larger fish, aquascaping

Offers excellent stability and long-term flexibility.

How to Choose the Right Aquarium Size by Litres

• Under 20L - very limited, mostly for shrimp
• Around 60L - best starting point for beginners
• Around 120L - ideal for community fish
• 240L+ - best for long-term setups and flexibility

Use litres as a guide, but always confirm the tank’s real shape and usable space.

Aquarium Dimensions by Gallons

Many aquarium guides use gallons rather than litres, so understanding aquarium dimensions in gallons is essential, especially when comparing UK and international tank sizes.

Below are the most common fish tank sizes in gallons, along with typical dimensions and conversions:

5 Gallon Aquarium Dimensions

• Approx size: ~40 × 20 × 25 cm
• Volume: ~19 litres
• Best for: shrimp, nano tanks

Best kept for shrimp or very small, carefully managed setups.

10 Gallon Tank Dimensions

• Approx size: ~50 × 25 × 30 cm
• Volume: ~45 litres
• Best for: small beginner setups

Often considered the minimum for beginner fishkeeping.

20 Gallon Tank Dimensions

• Long: ~75 × 30 × 30 cm
• High: taller design with less footprint
• Volume: ~90 litres

The “long” version is usually better for fish due to increased swimming space.

30 Gallon Aquarium Dimensions

• Approx size: ~90 × 30 × 40 cm
• Volume: ~135 litres
• Best for: community fish

Offers a good balance between size and manageability.

65 Gallon Aquarium Dimensions

• Approx size: ~120 × 45 × 45 cm
• Volume: ~240–250 litres
• Best for: larger fish and advanced setups

Provides excellent stability and aquascaping space. 

Why Gallons Can Be Misleading

• Two tanks with the same gallon rating can have different shapes and dimensions
• “Tall” tanks often have less usable swimming space
• Always compare full aquarium dimensions (length × width × height), not just gallons

If you’re in the UK, it’s usually easier to compare tanks using litres and cm, which we covered in the previous section.

Best Aquarium Dimensions for Different Fish Types

Choosing the right aquarium dimensions depends not just on size, but on the type of fish you plan to keep.

• Betta fish
  - Prefer 20L–40L tanks with calm water and moderate space
  - small but stable setups work best
• Community fish
  - Need 90L–180L aquariums with a larger footprint
  - more space improves compatibility and stability
• Active fish species
  - Require longer tanks
  - prioritise length over height for swimming space
• Aquascaping setups
  - Benefit from deeper tanks (greater width and depth)
  - allows more layout flexibility and plant placement

Different fish need different aquarium dimensions, not just different tank sizes.

Aquarium Dimensions Calculator (Volume in Litres)

You can use a simple formula to calculate aquarium volume based on tank dimensions. This works as a basic aquarium dimensions calculator for any rectangular fish tank.

Formula:

Length × Width × Height ÷ 1000 = Litres

Example Calculation:

If your aquarium measures:

• Length: 60 cm
• Width: 30 cm
• Height: 30 cm

60 × 30 × 30 ÷ 1000 = 54 litres

How to Calculate Aquarium Volume (Step-by-Step)

1. Measure the tank in centimetres (cm)
2. Multiply length × width × height
3. Divide the result by 1000
4. The result is the tank volume in litres

Gross Volume vs Real Water Volume:

This formula gives the gross volume of the aquarium, not the actual usable water volume.

In reality, your tank will hold less water due to:

• substrate (gravel or sand)
• decorations and hardscape
• internal equipment (filters, heaters)
• water level below the rim

In most cases, the real water volume is 10–20% lower than the calculated value.

Quick Tip:

Always use real (adjusted) volume when calculating:

• fish stocking
• filtration requirements
• water treatments

For a quick comparison, you can also use the aquarium size chart above to estimate volume without calculating manually.

Why Width Matters More Than Most Beginners Think

This is one of the most overlooked parts of choosing an aquarium. Most beginners focus on aquarium height, but in reality, width (depth) and overall footprint are far more important for fish health and tank stability.

The aquarium footprint (length × width) determines how much usable space fish actually have, not just the total litres.

Benefits of a Wider Aquarium

• More swimming space
  Fish swim horizontally, so a wider and longer tank allows more natural movement and reduces stress
• Better oxygen exchange (surface area)
  A wider tank increases the water surface area, improving gas exchange and oxygen levels
• Easier aquascaping and layout
  More depth gives you space for plants, rocks and décor without overcrowding
• More stable water conditions
  Tanks with a larger footprint are generally more stable and easier to maintain

Long vs Tall Aquariums

• A long, wide aquarium provides better swimming space and stability
• A tall, narrow tank often limits usable space and can be harder to maintain

This is why two aquariums with the same litre capacity can perform very differently depending on their dimensions.

Quick Tip:

When choosing an aquarium, prioritise length and width over height, especially for beginner setups.

Aquarium Weight: Empty vs Filled

Aquarium weight is often underestimated, but it’s one of the most important factors to consider when setting up a fish tank, especially in UK homes.

How Much Space Do You Need for an Aquarium?

Before choosing an aquarium, it’s important to understand how much space it will actually require in your home.

When planning your setup, consider:

• Cabinet size and clearance
  Make sure the aquarium stand fits comfortably with extra room for maintenance
• Wall space and placement
  Avoid tight corners or unstable surfaces
• Distance from windows
  Too much sunlight can cause algae growth and temperature fluctuations
• Floor strength (especially upstairs)
  Larger aquariums can become very heavy when filled

Larger aquariums require more planning, especially in smaller UK homes.

How Much Does an Aquarium Weigh?

A simple guideline is:

1 litre of water = 1 kg

This means:

• A 100L aquarium holds ~100 kg of water
• A 120L tank holds ~120 kg of water

But this is only the water weight.

Total Weight of a Filled Aquarium

The actual weight of a fish tank includes:

• Glass tank (heavy, especially larger tanks)
• Substrate (gravel or sand)
• Decorations and hardscape
• Equipment (filters, heaters, lighting)

A 120L aquarium can easily weigh 130–150 kg or more when fully set up.

Why Aquarium Weight Matters

• Furniture strength
  Not all cabinets can safely support a filled aquarium
• Floor load capacity
  Important for upstairs rooms or older buildings
• Cabinet compatibility
  Always use a stand designed for the aquarium's weight

Always check the total filled weight of your aquarium, not just the empty tank weight, before choosing where to place it. 

Common Mistakes When Choosing Aquarium Dimensions

This is where many beginners go wrong when choosing an aquarium:

• Choosing a tank based only on litres, not dimensions
  - Two tanks with the same volume can have completely different usable space
• Picking a tall tank instead of a wider one
  - Reduces swimming space and limits oxygen exchange
• Buying a tank that is too small for long-term use
  - Smaller tanks are less stable and harder to maintain
• Ignoring the total weight of a filled aquarium
  - Can lead to unsafe setups or damaged furniture
• Not accounting for internal space loss
  - Substrate, décor and equipment reduce usable water volume

Most issues with aquarium setups come from choosing the wrong dimensions, not the wrong equipment.

How to Measure Aquarium Dimensions Correctly

Measuring aquarium dimensions correctly is essential when calculating volume, choosing furniture, or planning your setup.

Step-by-Step: How to Measure Aquarium Dimensions 

Follow these steps to measure aquarium dimensions accurately:

1. Measure the external dimensions
   • Length, width and height of the tank from the outside
   • Used for placement, furniture and cabinet fit
2. Measure the internal dimensions
   • The usable space inside the tank
   • Important for calculating actual water volume
3. Check the glass thickness
   • Thicker glass reduces internal space slightly
   • More noticeable in smaller tanks
4. Account for the water level
   • Tanks are rarely filled to the very top
   • Leave space below the rim for safety
5. Consider equipment and layout
   • Filters, heaters and décor take up space
   • This reduces usable volume

External vs Internal Aquarium Dimensions

Aquarium dimensions can be measured in two ways, and understanding the difference is essential when setting up your tank.

• External dimensions
  These refer to the outer measurements of the aquarium and are used when checking:
  • cabinet fit
  • available space
  • room placement
• Internal dimensions
  These measure the usable space inside the tank and are used for:
  • calculating water volume
  • fish stocking
  • aquascaping

Even small differences in internal dimensions can significantly affect the actual water volume.

Why Accurate Aquarium Measurements Matter

Accurate aquarium measurements are essential for planning a safe and successful setup.

• Prevents buying the wrong furniture or cabinet
  Incorrect measurements can lead to tanks not fitting properly or being unsupported
• Ensures correct volume calculations
  This is critical for filtration, heating and water treatments
• Improves fish stocking decisions
  Using incorrect dimensions can lead to overcrowding or unstable conditions
• Helps avoid costly mistakes
  Small errors in measurement can result in poor setup choices or safety risks

Taking accurate measurements from the start makes your aquarium easier to manage and more stable long-term.

Always measure the usable space inside the aquarium, not just the outer dimensions. For example, a tank advertised as 60 × 30 × 30 cm may have slightly less internal space due to glass thickness and water level, resulting in a lower actual volume. 

Now that you understand dimensions, here’s how to turn that into a practical buying decision.

Which Aquarium Size Should You Choose?

Choosing the right aquarium size depends on your experience level, available space and the type of fish you want to keep. Litres help you compare volume, but dimensions show how usable that space is for fish.

Best Aquarium Size for Beginners (UK)

60L–100L aquariums are ideal for beginners

• Provide more stable water conditions
• Easier to maintain than very small tanks
• Offer enough space for small community fish

Smaller tanks (under 40L) are often harder to manage and less forgiving for beginners.

Best Tank Size for Betta Fish

20L–40L tanks are recommended for betta fish

• Avoid unstable nano setups
• Provide enough space for natural behaviour
• Easier to heat and filter properly

Very small tanks can lead to poor water quality and stress.

Best Aquarium Size for Community Tanks

90L–180L aquariums are ideal for community fish

• Allow a wider variety of species
• Provide a better swimming space
• Offer more flexibility for aquascaping

Larger tanks are generally more stable and easier to balance long-term.

Best Aquarium Size for Small UK Homes

If space is limited, focus on efficient aquarium dimensions rather than just litres.

• Prioritise length and width (footprint) over height
• Ensure the cabinet can support the full weight
• Choose a size that fits your available space comfortably

A well-sized 60L tank is often better than a tall, narrow aquarium with the same volume.

Quick Recommendation:

If you’re unsure, start with a 60L–90L aquarium, which offers the best balance between size, stability and ease of maintenance. 

How to Choose the Right Aquarium Based on Your Needs

Use this quick guide to match your situation with the right aquarium size:

• Limited space (small UK homes)
  - Choose a 60L–90L aquarium with a good footprint
  - easier to fit and maintain
• Keeping a betta fish
  - Choose a 20L–40L tank
  - stable enough while still compact
• Planning a community tank
  - Choose at least a 90L–120L aquarium
  - more space, better stability
• Beginner setup
  - Avoid tanks under 40L
  - small tanks are less stable and harder to manage
• Long-term setup or flexibility
  - Choose 120L+
  - easier to balance and expand over time

Quick Decision Guide

If you're unsure, follow this simple rule:

• Small space - 60L–90L
• Beginner - 60L–100L
• Community fish - 90L–180L
• Long-term setup - 120L+

FAQ

Below are answers to the most common questions about aquarium dimensions, tank sizes and volume calculations.

What are standard aquarium sizes?

Standard aquarium sizes refer to the most common aquarium dimensions used by manufacturers, such as 60cm, 90cm and 120cm tanks. In the UK, these are typically measured in centimetres (cm) and litres, making it easier to compare tank size and volume.

What are the aquarium dimensions in cm?

Aquarium dimensions in the UK are usually expressed in centimetres as length × width × height (L × W × H).
For example, a common beginner tank size is 60 × 30 × 30 cm, which equals roughly 54 litres.

What are the aquarium dimensions in inches?

Aquarium dimensions in inches are commonly used in US guides.
For example, a 60cm aquarium is approximately 24 inches long, but the full tank dimensions must still be considered for accurate comparisons.

How many litres is a 10 gallon tank?

A 10 gallon aquarium holds approximately 45 litres of water.
However, the actual usable volume is slightly lower due to substrate, decorations and equipment inside the tank.

What is the best aquarium size for beginners?

The best aquarium size for beginners is typically 60–100 litres, as it provides more stable water conditions and is easier to maintain than smaller tanks.
Larger tanks are generally more forgiving and better for long-term success.

Why does aquarium width matter?

Aquarium width affects the footprint and surface area of the tank, which influences swimming space, oxygen exchange and overall stability.
A wider aquarium usually provides better conditions for fish than a tall, narrow tank.

How heavy is a filled aquarium?

A filled aquarium typically weighs around 1 kg per litre of water, plus additional weight from the glass, substrate and decorations.
For example, a 120L aquarium can weigh 130–150 kg or more when fully set up.

What is the difference between tank size and water volume?

Tank size refers to the external aquarium dimensions, while water volume is the actual usable space inside the tank.
The real water volume is usually lower due to equipment, décor and the water level below the rim. 

What is the most common aquarium size?

The most common aquarium size in the UK is a 60cm tank (around 54–60 litres), which is ideal for beginners. It offers a good balance between stability, space and ease of maintenance compared to smaller tanks.

Is a longer tank better than a taller tank?

Yes, a longer aquarium is usually better than a taller tank because it provides more horizontal swimming space and better oxygen exchange. Fish benefit more from a larger footprint (length × width) than extra height.

How do I calculate aquarium litres?

To calculate aquarium litres, use this formula:
Length × Width × Height ÷ 1000 = Litres

Make sure measurements are in centimetres. The result gives the tank’s gross volume, while the actual water volume is usually slightly lower.

Are gallon sizes the same in the UK and US?

No, gallon sizes are not the same.
A UK gallon (4.54L) is larger than a US gallon (3.78L), which can lead to confusion when comparing aquarium sizes. Always check whether values are listed in UK or US gallons.

Conclusion

Aquarium dimensions are more than just numbers; they directly affect fish health, water stability and the long-term success of your setup.

While litres and gallons are useful for comparison, the most important factor is understanding the full aquarium dimensions (length, width and height), especially the tank’s footprint. In most cases, a longer and wider aquarium will provide better conditions than a tall, narrow one.

For UK fishkeepers, focusing on cm measurements, litre capacity and real-world usability makes it much easier to choose the right aquarium size for your space and your fish.

If you use this guide to compare aquarium dimensions, understand volume and choose based on purpose, not just numbers, you’ll make a far better decision from the start.

Final Recommendation

If you're unsure, start with a 60L–90L aquarium with a good footprint, which offers the best balance between stability, usability and ease of maintenance. 

Based on practical experience with beginner and community aquariums, tanks with a larger footprint are consistently easier to maintain and provide better long-term stability.

This guide was created by the AquaticsHub team, UK-based aquarists focused on practical, welfare-first fishkeeping.