Answer first
What this calculator tells you
Calculate an aquarium's volume in gallons and liters, and the weight of the water it holds. Check the size of the tank before you buy a filter, a heater or a stand. Formula: Gallons = length × width × height ÷ 231 (cubic inches per US gallon); water weight = gallons × 8.34 lb. At the worked-example inputs, the volume (US gallons) is 54. Holding every other input steady, moving length (in) from 38 to 58 moves the result from 42.8 to 65.3.
Transparent method
The formula
Check the size of the tank before you buy a filter, a heater or a stand.
Worked example
Example inputs
How to interpret the result
Tank size drives everything you buy for it, from the heater to the filter to the stand. A 48 by 13 by 20 inch tank holds about 54 gallons when filled to the top of that height. Water weighs 8.34 pounds a gallon, so the water alone is over 450 pounds, before the glass, the gravel and the stand. That weight is why the floor under a large tank matters.
At the worked-example inputs the volume (US gallons) is 54. It rises with length (in), water height (in) and width (in).
Formulas assume ideal geometric shapes. Real-world measurements carry their own error, and every input must use the same unit: mixing feet and inches silently produces a wrong answer.
Before you rely on it
What to check
Measure the water height, not the outside height of the glass. A tank filled to two inches below the rim holds noticeably less than its label says.
The common error
Where people go wrong with aquarium volume calculator
Trusting the gallon number printed on the box. Glass thickness and the water line change the real volume, and a measured figure is more reliable.
Sensitivity evidence
How length (in) changes the volume (US gallons)
Holding every other input at the worked-example value, moving length (in) from 38 to 58 moves the volume (US gallons) from 42.8 to 65.3: a spread of 22.5, or 42% of the worked-example result.
| Length (in) | Volume (US gallons) | Water weight (lb) | Volume (liters) |
|---|---|---|---|
| 38 | 42.8 | 356.7 | 161.9 |
| 43 | 48.4 | 403.6 | 183.2 |
| 48worked example | 54 | 450.6 | 204.5 |
| 53 | 59.7 | 497.5 | 225.8 |
| 58 | 65.3 | 544.4 | 247.1 |
Every input, tested
Which input moves the volume (US gallons) most
Of the 3 inputs, length (in) moves the volume (US gallons) most (11.3 across the range tested) and width (in) moves it least (8.3).
| Input | Tested from | To | Volume (US gallons) at each end | Swing |
|---|---|---|---|---|
| Length (in) | 43 | 53 | 48.4 to 59.7 | 11.3 (21%) |
| Water height (in) | 18 | 22 | 48.6 to 59.4 | 10.8 (20%) |
| Width (in) | 12 | 14 | 49.9 to 58.2 | 8.3 (15%) |
Two variables at once
Volume (US gallons) by length (in) and width (in)
Across the grid the volume (US gallons) runs from 32.9 to 80.3. Moving length (in) from 38 to 58 shifts it by 22.5 at the middle column, and moving width (in) from 10 to 16 shifts it by 24.9 at the middle row, so width (in) is the bigger lever here.
| Length (in) \ Width (in) | 10 | 13 | 16 |
|---|---|---|---|
| 38 | 32.9 | 42.8 | 52.6 |
| 43 | 37.2 | 48.4 | 59.6 |
| 48 | 41.6 | 54 | 66.5 |
| 53 | 45.9 | 59.7 | 73.4 |
| 58 | 50.2 | 65.3 | 80.3 |
The highlighted cell is the worked example: 54.
Step by step
The worked example, input by input
| Input | Value used | What it means |
|---|---|---|
| Length (in) | 48 | Enter the length (in) used in this calculation. |
| Width (in) | 13 | Enter the width (in) used in this calculation. |
| Water height (in) | 20 | Measure the water level, not the top of the glass. |
| Volume (US gallons) | 54 | |
| Water weight (lb) | 450.6 | |
| Volume (liters) | 204.5 | |
Inputs, definitions and assumptions
Length (in)
Enter the length (in) used in this calculation. The prefilled worked-example value is 48.
Width (in)
Enter the width (in) used in this calculation. The prefilled worked-example value is 13.
Water height (in)
Measure the water level, not the top of the glass. The prefilled worked-example value is 20.
How to use this calculator
- 1Verify the inputs. Gather length (in), width (in) and water height (in) from your own documents; the prefilled values are examples.
- 2Save a baseline. The worked example puts the volume (US gallons) at 54. Store your own version of it as Scenario A.
- 3Test one change. Start with length (in), the input with the biggest effect here: moving length (in) from 43 to 53 takes the volume (US gallons) from 48.4 to 59.7, a swing of 21% of the worked-example figure.
- 4Check the extremes. At half the example length (in) (24) the volume (US gallons) is 27; at double (96) it is 108.1.
People also ask
Frequently asked questions
How do you calculate aquarium volume?
Gallons = length × width × height ÷ 231 (cubic inches per US gallon); water weight = gallons × 8.34 lb. At the worked-example inputs the volume (US gallons) is 54.
What does the aquarium volume result mean?
Check the size of the tank before you buy a filter, a heater or a stand. At the worked-example inputs the volume (US gallons) is 54. It rises with length (in), water height (in) and width (in).
How much does length (in) change the volume (US gallons)?
Holding every other input at the worked-example value, moving length (in) from 38 to 58 moves the volume (US gallons) from 42.8 to 65.3, a spread of 22.5.
What are the limits of this aquarium volume calculator?
Formulas assume ideal geometric shapes. Real-world measurements carry their own error, and every input must use the same unit: mixing feet and inches silently produces a wrong answer. The tables on this page test length (in) only from 38 to 58; a value outside that range is not tabulated here.
Which input moves the volume (US gallons) most in the aquarium volume calculator?
Ranked by how far each moves the volume (US gallons) across the range tested: length (in) (11.3, 21%), water height (in) (10.8, 20%) and width (in) (8.3, 15%).
If I double length (in) in the aquarium volume calculator, does the volume (US gallons) double?
Doubling it from 48 to 96 takes the volume (US gallons) from 54 to 108.1, which is 2.00 times the worked-example figure. So the result scales almost exactly in proportion. Halving it to 24 gives 27.
How much does width (in) matter in the aquarium volume calculator?
The worked example uses 13. With the other inputs left at the worked example, moving width (in) from 12 to 14 takes the volume (US gallons) from 49.9 to 58.2, a swing of 15% of the worked-example figure.
How much does water height (in) matter in the aquarium volume calculator?
The worked example uses 20. Holding every other input at its worked-example value, moving water height (in) from 18 to 22 takes the volume (US gallons) from 48.6 to 59.4, a swing of 20% of the worked-example figure.
Which inputs change the water weight (lb) in the aquarium volume calculator?
At the worked-example inputs it is 450.6. Length (in) takes it from 403.6 to 497.5, width (in) takes it from 415.9 to 485.2 and water height (in) takes it from 405.5 to 495.6.
Which inputs change the volume (liters) in the aquarium volume calculator?
At the worked-example inputs it is 204.5. Length (in) takes it from 183.2 to 225.8, width (in) takes it from 188.8 to 220.2 and water height (in) takes it from 184.1 to 225.
What is the difference between a radius and a diameter?
The diameter is the full width through the center and the radius is half of it. Each field label says which one it wants. Entering a diameter where a radius is asked makes an area four times too large and a volume eight times too large.
Sources and evidence
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