Free tool
Aquarium Volume Calculator NZ
Enter your fish tank's measurements to see how many litres it holds, the same figure in US and UK gallons, and roughly how much the water weighs. For a rectangular tank, the answer is length × width × height in centimetres, divided by 1,000.
Optional: real water volume
Gravel holds some water between the stones, so the true figure sits a little above this estimate. Decorations, rocks and wood take up space too.
Enter your tank's measurements to see its volume in litres and gallons. Measure the inside of the glass if you can — outside measurements include the glass and read slightly high.
How it works
The calculator works out the floor area of your tank's shape and multiplies it by the height. One litre is 1,000 cm³. A bow-front is treated as a rectangle plus a circular arc across the front; a corner tank as a quarter of a circle; a hexagon as six equal sides. Gallons use the exact conversions: 3.785 litres to a US gallon and 4.546 litres to a UK gallon.
The litres figure is the number you need for heater sizing, filter choice and water-conditioner doses. Use the real water volume, not the size printed on the box.
Keep reading
- Fish Tank Heater NZ — what size heater your litres need
- Aquarium Water Changes NZ — how much and how often
- How to Cycle a New Fish Tank — before any fish go in
- Aquarium Filter Types NZ — HOB, canister, sponge and internal
- How to Set Up Your First Aquarium — NZ beginner's guide
- Aquarium Fish Prices NZ — typical prices by species
Frequently asked questions
How do I work out how many litres my fish tank holds?
For a rectangular tank, multiply length × width × height in centimetres and divide by 1,000. A tank measuring 60 × 30 × 36 cm holds 64,800 cm³, which is 64.8 litres filled to the rim. For other shapes, the calculator above works out the floor area first and multiplies it by the height.
Why does my tank hold less water than its size?
The size on the box is usually measured to the rim, often from the outside of the glass. In use, the water sits below the rim, and gravel, sand, rocks and decorations take up space. Open "Optional: real water volume" in the calculator and enter the gap at the top and your substrate depth to estimate the water actually in the tank.
How much does a full fish tank weigh?
Fresh water weighs about 1 kg per litre, so a 100-litre tank holds roughly 100 kg of water. The glass, gravel, rocks and stand add to that. Before filling a large tank, check that the stand is rated for the load and sits level on a solid floor.
What is the difference between US and UK gallons?
A US gallon is 3.785 litres and a UK (imperial) gallon is 4.546 litres. Many tanks and products made for the US market are labelled in US gallons, so a tank sold as "20 gallons" usually means about 75.7 litres. New Zealand products normally use litres.
Which volume should I use when dosing water conditioner or treatments?
Use the water actually in the tank, not the size on the box, and follow the product label. For fish medicines, talk to a vet or an experienced aquarium retailer before dosing — some treatments harm invertebrates, plants or the filter bacteria.
How do I measure a bow-front tank?
Measure the length from left to right, the depth front-to-back at one end, and the depth front-to-back at the middle of the curve. The calculator treats the front as a circular arc, which is how most bow-front tanks are made. If your tank has a flat panel either side of the bow, the result will read slightly high.
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Shop at PetMall
The products below are practical support items for your pet. PetMall ships across New Zealand.
- Filters & MediaA good filter is the heart of a healthy tank — choose low-flow models for bettas and long-finned fish.
- Heating & LightingA heater is essential for tropical fish through NZ winters — most bettas and community fish want a stable 24–28°C.
- Water TreatmentDechlorinator and test kits are non-negotiable — stable water quality prevents most beginner fish losses.
- Fish FoodMatch food to your fish — floating pellets for bettas, sinking for bottom feeders. Feed small amounts your fish finish in a couple of minutes.
- Tank Cleaning & MaintenanceA gravel vacuum and an algae scraper do more for water quality than any gadget — most beginner tank problems are maintenance, not equipment.