Large Fish Tanks: Weight, Space and Where to Put One | Bossy Cat

Large fish tanks: how much they weigh, where to put one and what to check first

A big aquarium turns a corner of the living room into the thing everyone looks at. It's also one of the heaviest things you'll ever bring into the house, and once it's full of water you can't move it.

So before choosing the tank, it pays to choose the spot. This guide covers what a full tank weighs, how to work out whether your floor and wall can take it, and where it should and shouldn't go. Our aquariums range runs from PawHut desk tanks to Monster Shop 4ft cabinet kits, and the figures below come from those listings.

The quick answer

One litre of water weighs about 1kg. A full tank weighs its empty weight plus its capacity in kilos, plus gravel and decoration. A 300 litre tank and cabinet can weigh well over 400kg once filled, so it needs a solid, level floor, a spot away from sunlight and radiators, and a socket close by.

How much does a full fish tank weigh?

Work it out in three parts: the tank and cabinet empty, the water, and what goes inside.

Our Monster Shop 4ft 300 litre kit is a good example. The tank weighs 74kg and the cabinet 33kg, so 107kg empty. Add 300 litres of water, roughly 300kg, and the 25kg of gravel that comes with the kit, and you're past 430kg before ornaments and equipment.

Tank size	Water weight when full	Example from our range
3 litres	about 3kg	PawHut 3L nano starter kit
13 litres	about 13kg	PawHut 13L desk tank with filter and LED light
28 litres	about 28kg	PawHut 28L glass tank, PawHut 28L turtle tank
300 litres	about 300kg	Monster Shop 4ft tank and cabinet kits

Small tanks up to 28 litres sit happily on a sturdy desk or sideboard. Once you get into tens of litres, use a stand or cabinet made for the job. Large tanks always need their own cabinet.

Can my floor take a large fish tank?

Most ground floors on a concrete slab can. Suspended timber floors, upstairs rooms and older houses need more thought, because all that weight sits on a small patch of floor. The Monster Shop 300 litre kit stands on a footprint of just 120.5 x 39cm.

A few rules of thumb:

Ground floor beats upstairs. If you have a choice, put a large tank downstairs.
Against a wall, not mid-room. Floors are strongest near load-bearing walls, where the joists are supported.
Across the joists, not along them. On a timber floor, place the tank so its length runs across several joists rather than resting on one or two.
Ask before you fill. For a large tank upstairs or in an older property, get a builder or structural engineer to look at the floor first.

Where is the best place for a fish tank?

The RSPCA's advice on choosing an aquarium is to keep it away from heat sources, including direct sunlight. In practice that means:

Not in front of a window. Sunlight warms the water and feeds algae.
Not next to a radiator or fire. Heat swings make it harder to keep the water stable.
Near a socket. Filters, heaters and lights all need power. Our PawHut tank stands have power outlets built in.
Away from doors and busy walkways. Constant movement right next to the glass can startle fish, and a knock to the tank is the last thing you want.
On a level surface. Check the floor and the cabinet with a spirit level before filling.

Do I need a cabinet or a stand?

For anything bigger than a desk tank, yes. A purpose-built stand spreads the weight evenly and gives you somewhere to keep food, nets and water treatments.

Our PawHut fish tank stands are sized for tanks of 20 to 29 US gallons, which is about 76 to 110 litres. Both have cabinet storage and power outlets, and the white version includes an anti-tip kit. The Monster Shop 300 litre kits come with a matching cabinet that has two doors, an internal shelf and six feet to spread the load.

Don't put a large tank on a sideboard, chest of drawers or bookcase that wasn't made for it. Furniture that looks solid can bow under that much weight.

What comes with a large tank kit?

The Monster Shop 4ft 300 litre kits include the tank and cabinet, a filter in the lid rated at 1800 litres per hour, an air pump, a 300W heater, LED lighting, 25kg of gravel, a tree root ornament, artificial plants and a reversible background. The glass is 11mm thick and curved at the front.

The overall height, tank and cabinet together, is 143.5cm, so check it fits under shelves or a window sill.

Large fish tank checklist

Check	Why
Full weight	Empty weight + 1kg per litre + gravel
Floor	Ground floor, near a load-bearing wall, across the joists
Footprint and height	120.5 x 39cm and 143.5cm tall for our 4ft kits
Light and heat	Away from windows, radiators and fires
Power	A socket close by for filter, heater and lights
Base	A cabinet or stand built for the tank, checked with a spirit level

Tags: Aquariums, Buying guide, Fish tanks

Previous article Next article

Frequently asked questions

How much does a 300 litre fish tank weigh?

Well over 400kg when full. Our Monster Shop 4ft 300 litre fish tank weighs 74kg and its cabinet 33kg, so 107kg empty. Add about 300kg of water, since one litre weighs roughly 1kg, plus the 25kg of gravel in the kit, and the total passes 430kg before ornaments and equipment.

Can I put a large fish tank upstairs?

You can, but check the floor first. A large fish tank puts all its weight on a small area: our 300 litre kit stands on 120.5 x 39cm. Upstairs and older timber floors are weaker than a ground floor slab, so place the tank against a load-bearing wall, across the joists, and ask a builder or structural engineer before filling.

Where should I not put a fish tank?

In front of a window or next to a radiator. The RSPCA advises keeping an aquarium away from heat sources, including direct sunlight, which warms the water and feeds algae. Keep a fish tank away from doors and busy walkways too, and make sure there's a socket nearby for the filter, heater and lights.

Does a large fish tank need a cabinet?

Yes. A large fish tank needs a cabinet or stand built to carry its weight, as ordinary furniture can bow. Our Monster Shop 300 litre kits come with a matching cabinet that has six feet, two doors and a shelf. For mid-size tanks, our PawHut stands suit tanks of about 76 to 110 litres and include power outlets.

What size fish tank stand do I need?

One made for your tank's size and weight. Our PawHut fish tank stands are built for 20 to 29 US gallon tanks, which works out at about 76 to 110 litres, or roughly 76 to 110kg of water. The white version adds an anti-tip kit. Check the stand's top measurements against the tank's footprint before ordering.

What comes with a 4ft aquarium kit?

Our Monster Shop 4ft 300 litre aquarium kits include the tank and matching cabinet, a lid filter rated at 1800 litres per hour, an air pump, a 300W heater, LED lighting, 25kg of gravel, a tree root ornament, artificial plants and a reversible background. The front glass is 11mm thick and curved, and the set stands 143.5cm tall.

How do I work out how heavy my fish tank will be?

Add three things together. Start with the empty weight of the tank and stand from the listing, add one kilo for every litre of water, then add the gravel and decoration. A 28 litre fish tank holds about 28kg of water, while a 300 litre tank holds about 300kg, which is why large tanks need a solid floor and a cabinet built for them.

Can I buy large fish tanks from Bossy Cat?

Yes. Our aquariums range includes Monster Shop 4ft 300 litre tank and cabinet kits, PawHut fish tank stands with power outlets, and smaller PawHut glass tanks from 13 to 28 litres. Delivery is free on all orders to UK mainland addresses and arrives in 3-5 working days, with no hidden fees. If you change your mind, you can return your order, but the return postage is paid by you.