Quick answer
Aquarium volume in gallons = length × width × water height (inches) ÷ 231. A 48 × 13 × 21 inch tank filled to 100% holds 56.7 gallons (214.7 litres) and about 473.4 lb of water.
Enter the tank dimensions, unit and how full it is. The calculator returns capacity and water weight.
Related tools: Pool Volume Calculator: Gallons of water in a rectangular, round or oval pool. Volume Converter: Convert litres, gallons, cups, spoons and more. Barrel Volume Calculator: Approximate capacity of a barrel from head diameter, bung diameter and length.
How to use the Aquarium Volume Calculator
- Enter length (above 0).
- Enter width (above 0).
- Enter water height (above 0).
- Choose unit: Inches and Centimeters.
- Enter filled to (%) (between 0 and 100). It starts at 100.
- Optionally, enter empty tank weight (optional) (lb) (0 or more).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Length | A number | > 0 |
| Width | A number | > 0 |
| Water height | A number | > 0 |
| Unit | Choose one: Inches; Centimeters | Starts at Inches |
| Filled to | A number, in % | > 0, ≤ 100, starts at 100 |
| Empty tank weight (optional) (optional) | A number, in lb | ≥ 0 |
Formula and method
Formula
gallons = length × width × height ÷ 231 (inches); water weight ≈ 1 kg per liter
IEEE-754 double precision; shown to the decimals indicated.
Fresh water is taken as 1 kg per liter; substrate and décor displace some water. Plan geometry only; confirm quantities with your supplier and local code before ordering.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Length = 48; Width = 13; Water height = 21; Unit = Inches; Filled to = 100.
| Result | Value |
|---|---|
| Capacity | 56.7 gal |
| Liters | 214.7 |
| Water weight (lb) | 473.4 |
Example 2
Inputs: Length = 60; Width = 18; Water height = 20; Unit = Inches; Filled to = 90; Empty tank weight (optional) = 40.
| Result | Value |
|---|---|
| Capacity | 84.2 gal |
| Liters | 318.6 |
| Water weight (lb) | 702.3 |
| Total weight with tank (lb) | 742.3 |
Example 3
Inputs: Length = 100; Width = 40; Water height = 50; Unit = Centimeters; Filled to = 100.
| Result | Value |
|---|---|
| Capacity | 52.8 gal |
| Liters | 200 |
| Water weight (lb) | 440.9 |
The first line is the headline result (capacity). Below it the aquarium Volume Calculator lists liters and water weight (lb), which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Water weight matters
Water weighs about 8.34 lb per US gallon, so 56.7 gallons is 473 lb before glass, gravel and stand. Check the floor and stand can bear it. A 100 gallon tank weighs well over 1,000 lb filled.
Fill level
Tanks are never filled to the brim: rimless tanks are often filled lower. Use the percentage filled input, and subtract about 5 to 10% for substrate and decor, which displace water.
How the result changes with length
Holding every other input at the first worked example, this table changes only length. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Length | Capacity | Liters | Water weight (lb) |
|---|---|---|---|
| 24 | 28.4 gal | 107.4 | 236.7 |
| 48 | 56.7 gal | 214.7 | 473.4 |
| 96 | 113.5 gal | 429.5 | 946.8 |
| 192 | 226.9 gal | 858.9 | 1,893.6 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Length: entering "0" shows "Length must be greater than 0." beside that field and no result.
- Filled to: entering "0" shows "Filled to must be greater than 0." beside that field and no result.
Choosing between the Aquarium Volume Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Pool Volume Calculator](/construction/pool-volume-calculator/) | shape, length and average depth | Pool volume |
| [Volume Converter](/converters/volume-converter/) | value, from and to | US gallon → Litre (L) |
| [Barrel Volume Calculator](/math/barrel-volume-capacity-calculator/) | head diameter, bung diameter and inside length | Capacity |
| [Aquarium Tank Volume Calculator](/math/aquarium-tank-volume-calculator/) | length, width and water height | Volume |
| [Cubic Yards Calculator](/construction/cubic-yards-calculator/) | length, width and height or depth | Volume |
Background: construction estimates
Material quantities are geometry plus a margin. Calculate the exact volume or area, add an allowance for waste, spillage, cuts and uneven ground (calculator pages commonly mention 5 to 10 percent, a rule of thumb that varies by material and job) and round up to whole units. One cubic yard is exactly 27 cubic feet.
Suppliers often have minimum order sizes and may charge for small loads, so confirm quantities, product yields and local code with your supplier or a qualified estimator before ordering.
Assumptions and limitations
- Rimless tanks are filled to a lower level
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for length and filled to to confirm this.
Frequently asked questions
How do I convert gallons to litres?
Multiply gallons by 3.785 to get litres.
Should I use inside dimensions?
Yes, inside measurements give true capacity.
Does it work for a cylinder tank?
Use the Cylinder Cubic Footage calculator.
What does the Aquarium Volume Calculator calculate?
Capacity and filled weight of a rectangular aquarium. It returns Capacity, Liters and Water weight (lb).
What formula does the Aquarium Volume Calculator use?
gallons = length × width × height ÷ 231 (inches); water weight ≈ 1 kg per liter. Fresh water is taken as 1 kg per liter; substrate and décor displace some water.
What do I need to enter in the aquarium Volume Calculator?
You enter Length, Width, Water height, Unit and Filled to (%). Optional: Empty tank weight (optional) (lb).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Rimless tanks are filled to a lower level.
What does the “Unit” option change?
It sets how the aquarium Volume is worked out. The choices are Inches and Centimeters.
What is an example of a aquarium Volume result?
With length 48, width 13, water height 21, unit Inches and filled to 100, the capacity is 56.7 gal.
Can I rely on this calculator for a decision?
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work. For this calculator in particular: Rimless tanks are filled to a lower level.
Related calculators
- Pool Volume Calculator — Gallons of water in a rectangular, round or oval pool.
- Volume Converter — Convert litres, gallons, cups, spoons and more.
- Barrel Volume Calculator — Approximate capacity of a barrel from head diameter, bung diameter and length.
- Aquarium Tank Volume Calculator — Volume of a rectangular tank in litres and US gallons.
- Cubic Yards Calculator — Cubic yards, cubic feet and cubic meters from length, width and height.
- Cylinder Cubic Footage Calculator — Volume of a cylinder (pipe, tank, column) in cubic feet, cubic yards, gallons and liters.
- Beer Volume Converter — Convert kegs, cans, bottles, pints and litres of beer.
- Workout Volume Calculator — Total lifted volume from sets, reps and weight.
- Excavation Volume Calculator — Soil volume to dig for a pit, trench or foundation, with an optional swell factor.
Sources
- OpenStax, Prealgebra 2e (Rice University): perimeter, area, volume, circumference and the Pythagorean theorem
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B conversion factors (international foot 0.3048 m, inch 25.4 mm, US gallon 3.785411784 L)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.