Betta Fish Tank Size UK Guide: 5 Gallon / 10L / 20L / 30L / 40+L

Choosing the right betta fish tank size in the UK is one of the most confusing parts of starting in fishkeeping.
Online advice often contradicts itself: some sources mention 5 litres, others 5 gallons, while many still promote tiny bowls or decorative “betta kits” that look appealing but perform poorly in real UK homes.

This guide cuts through that confusion and explains what tank sizes actually work long-term in the UK, using litres (with gallon conversions), real UK home conditions, based on water stability, temperature control, maintenance effort and betta welfare, not outdated myths or marketing.

Quick answer: 

In the UK, the minimum tank size we recommend for a betta fish is 20–30 litres (≈ 5–8 gallons), with 30–40L being ideal for beginners.

While bettas can survive in smaller tanks, UK home temperatures, winter heating patterns and water stability make larger tanks significantly easier to maintain and far better for long-term welfare. 

These recommendations align with modern betta welfare guidance and the experience of UK-based aquarists, not just theoretical minimums. (More information in our full betta fish care guide for UK homes). 

In short, bigger tanks are not about luxury; they are about stability and ease. 

This UK guide covers:

Before diving into details, here’s exactly what you’ll learn in this UK-focused guide:

• What size tank does a betta fish really need in the UK
• The difference between 5 gallon vs 10L vs 20L vs 30L and 40L+ tanks
• Whether 5L or 10L tanks are actually suitable
• Betta fish tank size in litres, cm and inches
• How UK homes (flats vs houses) affect tank choice
• Special cases like giant bettas and future tank mates 

Quick navigation: 

• What size tank does a betta need? (UK reality)
• Why tank size matters more than people think
• Minimum tank size for 1 betta fish in the UK
• 10L vs 20L vs 30L betta tanks in the UK
• 10L vs 20L vs 30L vs 40L+ (UK comparison)
• Betta fish tank size in litres, cm and inches
• How much space does 1 betta fish really use?
• Special cases: when you need more than the minimum
• How tank size affects equipment choice (UK)
• Cost and maintenance by betta tank size (UK)
• Can betta fish live in very small tanks?
• Frequently asked questions
• Final Thoughts

What size tank does a betta need? (UK reality)

This is the most common question that UK fishkeepers ask, and it is also the one with the most conflicting answers online.

Much of the confusion stems from combining US advice, outdated minimums, and UK-specific realities, such as colder winters and smaller indoor spaces.

UK verdict: minimum vs recommended vs ideal

Based on modern betta welfare standards and real UK home conditions:

• Minimum ethical size (UK): 15–20 litres
• Recommended for beginners: 20–30 litres
• Ideal long-term size: 30–40 litres or more

In UK conditions, larger tanks are easier to maintain, provide better temperature stability, slower water chemistry changes, and far less daily stress for both the fish and the keeper, especially during UK winters.

Why tank size matters more than people think

At first glance, a betta looks like a small fish that doesn’t swim much. This leads many beginners to assume that a small tank is “good enough”.

In practice, tank size affects almost every aspect of betta health.

How tank volume affects temperature and water quality in UK homes

In the UK, indoor temperatures can fluctuate significantly:

• Heating is turned off overnight,
• Winter temperature drops are common.
• Colder rooms in winter,
• Warm spells in summer without air conditioning.

In small tanks, these changes happen fast.

The same applies to water quality:

• Ammonia spikes faster in small volumes,
• Mistakes are less forgiving,
• Maintenance must be more frequent.

In a 10L tank, temperature and water chemistry can change within hours.
In a 30L tank, the same changes happen much more slowly, giving heaters and filters time to compensate.

Why tiny tanks and bowls fail (5L, jars, ornaments)

This leads directly to the common question: Is 5L enough for a betta fish?

The short answer is NO. 

A 5L tank is too small to maintain a stable temperature or water quality in UK homes, even with frequent water changes. These setups consistently result in stress and long-term health problems.

In tanks around 5 litres:

• temperature swings are extreme,
• filtration is often ineffective or absent,
• waste builds up rapidly,
• Stress levels remain high even with frequent water changes.

These setups may keep a betta alive in the short term, but they consistently fail as long-term habitats, especially in UK conditions.

Minimum tank size for 1 betta fish in the UK

People often ask, “What size tank for 1 betta fish?” They are usually looking for a clear number, not a debate. The real answer depends on units and context.

Here is the honest UK answer.

Why 5L and 5 gallons are often quoted, and why they’re not the same

This is the biggest source of confusion:

• 5 litres = extremely small (not suitable)
• 5 gallons ≈ 19 litres (very different)

Many beginners accidentally follow 5L advice, thinking it equals 5 gallons. It doesn’t.

While 5 gallons is not wrong, it often represents:

• a bare minimum,
• under ideal conditions,
• with experienced maintenance.

For UK beginners, we recommend slightly more headroom.

Recommended betta fish tank size: 20L vs 30L vs 40L+

Below is how common tank sizes compare in real UK homes:

If you’re looking for a 5-gallon / 20–40L betta-friendly tank, you can browse suitable options in our UK store.

10L vs 20L vs 30L betta tanks in the UK

This comparison comes up constantly, especially when choosing a first aquarium, and this is where most beginners hesitate.

Each size can house a betta, but not with the same margin of safety.

Can betta fish live in a 10-litre tank?

Yes, a betta can survive in a 10L tank, but in the UK, this requires:

• precise heater control,
• frequent water changes,
• little tolerance for mistakes.

A 10L tank is not beginner-friendly and is best treated as an advanced or temporary solution.
(For a full breakdown, see our dedicated 10L tank guide.)

Can a betta live in a 20-litre tank?

Yes, and this is where things become realistic for most UK keepers.

A 20L tank offers:

• improved thermal stability,
• better filtration options,
• reduced maintenance stress.

20L is the minimum size we confidently recommend for beginners.

Why 30–40+L is easier for beginners in UK homes

Despite being larger, 30–40+L tanks are actually:

• more forgiving,
• more stable,
• easier to maintain weekly.

For many UK homes, this range offers the best balance between space, cost and long-term success.

10L vs 20L vs 30L vs 40L+ (UK comparison)

Seeing the differences side-by-side makes the choice clearer. Here is a UK-specific comparison focused on real-world conditions.

UK home comparison: stability, maintenance and stress

Best tank size for UK flats vs UK houses

• UK flats: 20–30L usually fits space constraints while remaining stable
• UK houses: 30–40L+ offers maximum stability with minimal extra effort

Betta fish tank size in litres, cm and inches

Many searches focus on measurements rather than volume alone. This is useful, but only if interpreted correctly.

Litres vs gallons: quick UK conversion

• 5 gallons ≈ 19 litres
• 8 gallons ≈ 30 litres
• 10 gallons ≈ 38 litres

UK fishkeeping standards should always prioritise litres, not US gallons.

Why footprint matters more than height for betta fish

Bettas are surface-oriented fish.
A wider footprint allows:

• easier swimming,
• better access to air,
• more room for plants and resting spots.

Tall, narrow tanks often look attractive but perform poorly for bettas.

How much space does 1 betta fish really use?

Although bettas are not fast swimmers, they are territorial and actively explore their environment.

Swimming behaviour, territory and rest zones

A healthy betta:

• patrols its territory,
• rests on leaves and décor,
• frequently returns to the surface.

Cramped tanks restrict this natural behaviour.

Layout examples for a 20–30L betta tank

In a well-sized tank, you can comfortably include:

• live or silk plants,
• shaded resting spots,
• clear surface access.

This is much harder to achieve below 20L.

Special cases: when you need more than the minimum

Some bettas simply need more space than average. Larger tanks offer better stability, calmer behaviour, and make daily care, including feeding, much easier to manage.
If you’re unsure how feeding habits affect water quality, read our guide on how feeding affects water quality.

Giant/king betta tank size

Giant bettas have larger bodies, produce more waste, and need more room.
40 litres or more is strongly recommended.

Female betta sororities (advanced only)

Sororities require:

• large volumes (75–80 litres),
• careful stocking,
• constant monitoring.

A minimum of 75–80 litres is required, and they are not suitable for beginners.

How tank size affects equipment choice (UK)

Tank size directly influences which equipment works safely and efficiently.

Heater wattage by tank size in UK rooms

Larger tanks:

• hold heat longer,
• require less aggressive heaters,
• experience fewer temperature swings.

Filter flow and surface agitation in small vs larger tanks

In very small tanks, even gentle filters can create excessive flow. Larger tanks allow better control and balance. 

See our curated betta tank setup kits sized for 20–40L aquariums.

Cost and maintenance by betta tank size (UK)

Bigger tanks are often assumed to be more expensive, but that’s not always true long-term.

Setup and running costs: 20L vs 30L vs 40L

While initial costs rise slightly, maintenance effort usually drops as size increases.

Weekly maintenance effort by tank size

• 10L: frequent, unforgiving
• 20L: manageable
• 30–40L: easiest to maintain

Can betta fish live in very small tanks?

This question keeps resurfacing, so it’s worth answering clearly.

Is 5L enough for betta fish?

No.
A 5L tank cannot provide stable temperature or water quality in UK homes and should not be used for long-term betta care.

Are small “betta kits” suitable in the UK?

Many nano kits are undersized and marketed misleadingly. Always check the actual volume in litres, not the label.

Frequently asked questions

What size tank does a betta need in the UK?

At least 20–30L, with 30–40L being ideal.

Can betta fish live in a 10-litre tank?

They can survive, but it is not recommended for beginners.

Can a betta live in a 20-litre tank?

Yes, this is the minimum size we recommend.

Is a 5-gallon fish tank big enough for a betta?

It can work, but slightly larger tanks are easier in UK conditions.

What size tank for 1 betta fish and a few snails?

30L or more is recommended.

Final Thoughts

TL;DR – UK verdict

• 5L: ❌ not suitable
• 10L: ⚠️ advanced only
• 20L: ✅ minimum recommended
• 30L: ⭐ best choice for most UK homes
• 40L+: 🏆 ideal long-term

When you’re setting up your first betta tank in the UK, choosing the right size from the start will save money, reduce stress, and dramatically improve your chances of long-term success.  If you're unsure which tank size fits your space, budget, or experience level, start with 30–40L, as it offers the highest success rate for UK beginners.

These ranges reflect both modern welfare guidance and what experienced UK betta keepers have found to work reliably in real homes.

Guide written by the AquaticsHub team – UK-based aquarists.