Why does my tank hold less than its rating?

Tank ratings use outside dimensions. Glass thickness, substrate and the gap below the rim typically remove about a fifth, which matters when dosing per litre.

How heavy will it be?

Water is a kilogram per litre, plus glass and substrate. A 100 litre tank is comfortably over 130 kg filled, which is more than many pieces of furniture are built for.

Everydaypets

Aquarium Volume Calculator

Actual aquarium water volume, which is typically a fifth below the nominal figure. Glass thickness, substrate and the gap below the rim all displace water, and dosing by nominal volume overdoses the tank.

Also called: fish tank volume, aquarium litres calculator.

Water volume

106.88

106.88 litres of water, against a nominal 141.75 litres from the outside dimensions. Substrate, freeboard and glass take out 34.87 litres, which is 24.6% of the nominal. Filled, it weighs about 157.1 kg. Water alone is a kilogram per litre. With glass and substrate a filled tank is heavier than most furniture is rated for.

Nominal volume

141.75

Volume not water

34.87

Share not water

24.6

Filled weight

157.1

In US gallons

28.24

Filter flow for 5x turnover

534.4

On the weight

Water alone is a kilogram per litre. With glass and substrate a filled tank is heavier than most furniture is rated for.

How this is calculated

Method and background

How this is calculated

Outside dimensions overstate water volume three times over: the glass takes its own thickness from each side, the substrate occupies the bottom, and the tank is never filled to the rim. On a typical tank that is around twenty percent, which matters because medication and fertiliser are dosed per litre. The filled weight is the other number worth having before choosing where to put it: water alone is a kilogram per litre, and glass and substrate add more.

internal dimensions less substrate and freeboard, which is a fifth less than the outside suggests

t: Glass thickness
s: Substrate depth
f: Freeboard

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

a 90 by 35 by 45 cm tank

Length: 90 cm
Width: 35 cm
Height: 45 cm
Substrate depth: 5 cm
Gap below the rim: 3 cm
Glass thickness: 0.8 cm

Water volume106.88

88.4 x 33.4 x 36.2 / 1000

Open this example

no substrate or freeboard leaves more water

Length: 90 cm
Width: 35 cm
Height: 45 cm
Substrate depth: 0 cm
Gap below the rim: 0 cm
Glass thickness: 0.8 cm

Water volume130.5

boundary: only the glass displaces

Open this example

Method and limits

What it assumes

Water at one kilogram per litre and substrate at about 1.5 times that.

What it deliberately does not model

Rocks, wood and equipment displace further volume not counted here.
A bowed-front or curved tank needs its own calculation.

Formula version 1.0.0 · definition 1.0.0 · India · Report a problem with this calculator

Frequently asked questions

Why does my tank hold less than its rating?: Tank ratings use outside dimensions. Glass thickness, substrate and the gap below the rim typically remove about a fifth, which matters when dosing per litre.
How heavy will it be?: Water is a kilogram per litre, plus glass and substrate. A 100 litre tank is comfortably over 130 kg filled, which is more than many pieces of furniture are built for.