40 gallon fish tank: dimensions and equipment

A broad front-to-back footprint that changes layout and lighting coverage.

The extra front-to-back depth gives you more room to aquascape, but a narrow light may leave the front or back dim. Check how far the light spreads, not only its length.

36 3/16 in long18¼ in deep16 15/16 in high
See front view

U3 shown for scale. Positions and waterline are approximate; the checks below still apply.

Plan equipment for this tank →

Outside size of the Aqueon Standard 40 gallon breeder. For the water it holds, measure inside the glass.

What lives in a 40 gallon breeder

187 fish and invertebrates in our guide fit a 40 gallon tank as adults. Here is an example group drawn to scale, then the most popular choices.

All fish for a 40 gallon →
To scale: 8 harlequin rasboras, 6 bronze corydoras and a pearl gourami at adult size. An example group; check your own fish in this tank.

This tank, its lid and its stand

Tank format
Aqueon Standard 40 gallon breeder; 36 3/16 × 18¼ × 16 15/16 in outside
Empty tank weight
Not published
Matching lid or top
100129040
Lid fit
36 × 18 in; one top
Matching stand
Aqueon Classic Pine Black, item 100151136

These sizes are for the Aqueon Standard 40 gallon breeder; another brand’s 40 gallon can differ. Lids fit a tank model, not a gallon number.

Aqueon’s dimensions sheet says 58 lb and its 2024 catalog says 49 lb. In the filled weight calculator, enter your own tank’s weight, or the higher figure to be safe.

Box sizes won’t tell you if a lid fits: measure the ledges the lid rests on, the openings either side of the center brace and the space for the strip at the back. Check the lid is the one made for this tank before you fit it.

Aqueon’s 2025 catalog lists this stand for this tank, which tells you they fit, not that it is in stock. Follow the stand’s assembly instructions. Aqueon doesn’t publish the stand’s weight, so the filled weight calculator leaves it blank.

Work out the filled weight → Add your substrate, rock, equipment and stand to see the total on the floor.

What to buy, in order

  • Buy the lid made for this tank (see below) and a stand built to carry it full, with room to open the cabinet and reach your equipment.

    Check stand and lid fit →
  • Choose gravel or soil and how deep you want it, then work out how much to buy from the inside size of the tank. Bags of different substrates weigh differently, so a pounds-per-gallon rule is only a rough guide.

    Work out how much substrate →
  • Compare a suitable HOB or canister with room for service access. If a canister is chosen, measure the door opening and usable cabinet height before selecting its body.

    Compare filters →
  • A sponge filter needs an air pump, airline and a check valve; choose a pump strong enough for your water depth. A hang-on-back or canister filter doesn’t need one, though a battery air pump makes a good backup in a power cut.

    Set up an air pump →
  • Decide the water temperature your fish need and how cold the room gets. Size the heater from the maker’s chart and your actual water volume, and check it with a separate thermometer.

    Size a heater →
  • Check the light spans your tank and how it mounts. For plants, compare PAR at your water depth where the maker publishes it; watts alone don’t tell you how much light reaches the bottom.

    Check light fit →
  • Get a kit that tests ammonia, nitrite, nitrate and pH; most master kits leave out GH and KH, so add those if your fish need them. Dose conditioner for new water by the bottle’s label.

    How to test your water →
  • Plan access to the back of the deeper footprint and a practical route for a larger water-change amount.

    Choose water-change tools →
  • Keep plugs dry and labeled, with a drip loop on every cord as the manuals show. If you add a battery backup air pump, test it before you need it.

    Set up the power safely →

Then set it all up, step by step, and cycle the tank before you add fish.

Checkmarks aren’t saved when you leave the page; print it to keep them.

Measure before you buy

Outside arrows include glass and trim. Measure between the inside glass faces for water volume.
The water stops below the rim, and gravel and decor take up some of the space, so your tank holds less than its size suggests.
  • The tank’s outside size and the stand it needs.
  • The inside size up to the waterline, and how much room gravel and rock take, for your actual water volume.
  • The rim trim, the gap to the wall, the lid openings and where the light mounts.
  • The cabinet opening, the hose route and room to lift out filter media.
  • How you’ll carry water, the bucket size and where the outlets are.

With those numbers, use the water volume calculator and the electricity cost calculator. The first-year cost calculator keeps a line for every supply, even before you know its price.

Filters rated for this tank size

The smallest filters their makers rate for a 40 gallon, one of each kind. Compare the space they need and the upkeep, then choose for the fish and plants you plan to keep.

Every filter for a 40 gallon, in or out →

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Drawing of an aquarium filter (not a photo of the Fluval U3)

Manufacturer-rated for aquariums up to 40 US gal; Fluval also suggests it as a second filter in larger tanks.

Fluval U3

Internal filter that sits under water inside the tank, with foam, carbon and biological media and a three-way outlet.

Consider: It sits inside the tank, so measure the space it needs: 10.5 × 3.25 × 4 in, plus room to tilt it off its bracket. Fluval says it can lie on its side in a shallow tank.

Drawing of an aquarium filter (not a photo of the hygger Double Biochemical Sponge Filter, Small)

hygger suggests it for 10–40 US gal aquariums.

hygger Double Biochemical Sponge Filter, Small

An air-driven filter with two ribbed sponges and a container of ceramic balls for the bacteria, run by an air pump. The outlet pipe extends and turns all the way round, and an air valve in the box sets how strong the flow is.

Consider: Two sponges give it more surface than a single sponge filter, but it needs an air pump, sold separately, and stands inside the tank.

Drawing of an aquarium filter (not a photo of the hygger Hang-on-back Canister Filter 7W)

Manufacturer-rated for 20–40 US gal aquariums; 153 GPH flow rate.

hygger Hang-on-back Canister Filter 7W

A closed filter box that hangs on the back of the tank, with its pump in the lid and adjustable flow, 0.5 US gal of media (250 g of ceramic rings, a black sponge and two 8D sponges) and three outlets to choose from: a straight pipe, a rain bar and a duckbill nozzle. A surface skimmer on the intake takes up the oily film.

Consider: Its skimmer can pull in baby shrimp and very small fish: hygger’s answer is a piece of sponge or mesh over the skimmer’s intake. Expect it to gurgle for the first hours, or up to two days, while the air works out of the box.

Photo credits

Real photographs from Wikimedia Commons, resized and cropped to fit; each is used under the license named.