Aquarium Calculator — Tank Volume in Gallons & Liters
Calculate tank volume and unit conversions, then estimate weight, stocking, substrate, and CO₂ values with practical aquarium planning guidance.
Aquarium Volume Calculator
Calculate your fish tank volume in US gallons, UK gallons, and liters from your tank dimensions.
Tank Volume Calculator
Calculate exact water volume in US Gallons, Liters, and UK Gallons for Rectangular, Bowfront, Cylinder, Hexagon, and Cube tanks.
Stocking Level Calculator
Estimate bio-load capacity based on fish length, surface area gas exchange, and filtration turnover rate.
Filled Tank Weight Calculator
Determine combined load of water, glass thickness, substrate, and equipment to assess floor loading.
CO₂ Bubble Rate Calculator
Calculate target CO₂ bubble rates per minute targeting 30 ppm dissolved CO₂ using pH and dKH water hardness metrics.
Substrate & Soil Calculator
Determine required pounds, kilograms, or bag counts (9L soil / 5lb retail) of aqua-soil, sand, or gravel for target bed depth.
Liters ↔ Gallons Converter
Convert aquarium volumes between liters, US gallons, and UK gallons instantly with freshwater weight per conversion.
Heater Wattage Calculator
Size your aquarium heater based on tank volume, room temperature, and target water temperature with split-heater advice.
Filter Flow Calculator
Calculate required filter GPH and turnover rate for your tank volume, water type, and filtration level.
Enter your aquarium's length, width, and height to calculate tank volume quickly. Use the result to understand your aquarium's water capacity for stocking, water changes, equipment sizing, and other aquarium planning calculations.
Fish Tank Volume Calculator: Gallons, Liters & Tank Size
Use this fish tank volume calculator to find your aquarium's capacity from its dimensions. Calculate tank volume in US gallons and liters, check common aquarium sizes, and estimate the actual water volume available after leaving space below the rim.
How to Calculate Aquarium Volume
For a rectangular aquarium, multiply the inside length × width × water height. If you measure in centimeters, divide the result by 1,000 to get liters. If you measure in inches, divide by 231 to get US gallons.
Gross Tank Volume vs. Actual Water Volume
A tank's calculated volume is its gross capacity. The actual water volume can be lower because of the water level below the rim, substrate, rocks, decorations, and equipment. For dosing and other calculations that depend on water volume, use the most accurate measured water volume available. Once calculated, apply your volume to the water weight calculator, aquarium stocking calculator, substrate calculator, and CO₂ calculator.
Common Aquarium Sizes: Gallons, Liters & Dimensions
Use these common aquarium sizes as a quick reference. Actual water volume can vary depending on the tank's internal dimensions, water level, glass thickness, substrate, and decorations.
| Aquarium Size | Approx. Liters | Common Dimensions |
|---|---|---|
| 5 gallon | 18.9 L | 16 × 8 × 10 in |
| 10 gallon | 37.9 L | 20 × 10 × 12 in |
| 20 gallon | 75.7 L | 24 × 12 × 16 in |
| 20 gallon long | 75.7 L | 30 × 12 × 12 in |
| 29 gallon | 109.8 L | 30 × 12 × 18 in |
| 40 gallon breeder | 151.4 L | 36 × 18 × 16 in |
| 55 gallon | 208.2 L | 48 × 13 × 21 in |
| 75 gallon | 283.9 L | 48 × 18 × 21 in |
How Many Liters Are in a Gallon?
1 US gallon equals approximately 3.785 liters. Aquarium sizes sold in gallons are usually referring to US gallons, so check the unit before converting or comparing tank capacities.
Fish Tank Dimensions to Gallons & Liters
Know your aquarium dimensions but not its capacity? Use the table below for common tank measurements, or enter your own length, width, and height in the calculator above.
| Tank Dimensions | Approx. Liters | Approx. US Gallons |
|---|---|---|
| 60 × 30 × 30 cm | 54 L | 14.3 gal |
| 60 × 30 × 40 cm | 72 L | 19.0 gal |
| 80 × 30 × 40 cm | 96 L | 25.4 gal |
| 90 × 30 × 40 cm | 108 L | 28.5 gal |
| 100 × 40 × 40 cm | 160 L | 42.3 gal |
| 120 × 40 × 50 cm | 240 L | 63.4 gal |
| 120 × 50 × 50 cm | 300 L | 79.3 gal |
| 150 × 50 × 60 cm | 450 L | 118.9 gal |
How Many Liters Is My Fish Tank?
Multiply the inside length × width × water height in centimeters, then divide by 1,000 to calculate liters. For US gallons, divide the cubic-centimeter result by 3,785.41. For the most accurate result, measure the actual inside dimensions and water height.
2 Foot, 3 Foot, 4 Foot and 5 Foot Aquarium Sizes
Aquarium length alone does not determine volume because width and height also matter. A 2-foot tank, 3-foot tank, 4-foot tank, or 5-foot tank can have different capacities depending on its dimensions. Enter all three measurements into the calculator for an accurate result.
Actual Aquarium Water Volume Calculator
Your aquarium's advertised size is not always the amount of water it actually holds. Water level, substrate, rocks, driftwood, decorations, and equipment can all reduce the usable water volume.
Gross Volume vs. Net Water Volume
Gross volume is the theoretical internal capacity of the empty tank. Net or actual water volume is the amount of water the aquarium contains after accounting for the normal water level and anything that displaces water inside the tank.
Why Actual Water Volume Matters
Actual water volume is useful when calculating water changes, aquarium treatments, medication doses, fertilizers, salt, and other products that are based on the amount of water in the tank. Knowing your net capacity is also useful for the aquarium water weight calculator. Use the manufacturer's dosing instructions and the most accurate water-volume measurement available.
How Much Water Does My Fish Tank Really Hold?
Enter your aquarium's inside length, width, and actual water height into the calculator above. For a more realistic estimate, account for substrate and other objects that displace water.
Aquarium Gallons to Liters Conversion
Convert aquarium volume between US gallons and liters using the table below. Aquarium gallons normally refer to US gallons, which are different from UK imperial gallons.
| US Gallons | Liters |
|---|---|
| 1 gallon | 3.79 L |
| 2 gallons | 7.57 L |
| 5 gallons | 18.93 L |
| 10 gallons | 37.85 L |
| 20 gallons | 75.71 L |
| 29 gallons | 109.77 L |
| 40 gallons | 151.42 L |
| 55 gallons | 208.20 L |
| 75 gallons | 283.91 L |
| 100 gallons | 378.54 L |
How Many Liters Are in an Aquarium Gallon?
One US gallon equals 3.78541 liters. To convert US gallons to liters, multiply the number of gallons by 3.78541. To convert liters to US gallons, divide the number of liters by 3.78541.
US Gallons vs. UK Gallons
A US gallon is approximately 3.785 liters, while a UK imperial gallon is approximately 4.546 liters. Check which gallon measurement a tank specification or aquarium product uses before comparing volumes.
Fish Tank Volume Formula
The fish tank volume formula depends on the shape of the aquarium. For a standard rectangular aquarium, multiply the inside length by the inside width and the water height, then convert the result to liters or US gallons.
Rectangular Fish Tank Formula
Liters = length (cm) × width (cm) × water height (cm) ÷ 1,000
US gallons = liters ÷ 3.78541
For measurements in inches:
US gallons = length (in) × width (in) × water height (in) ÷ 231
Example: Calculate a 60 × 30 × 30 cm Fish Tank
60 × 30 × 30 = 54,000 cubic centimeters.
54,000 ÷ 1,000 = 54 liters.
54 ÷ 3.78541 = approximately 14.27 US gallons.
So a 60 × 30 × 30 cm rectangular aquarium has a gross volume of approximately 54 liters or 14.27 US gallons before accounting for substrate, decorations, glass thickness, or space below the rim.
Why Use Inside Dimensions?
Use the inside dimensions and actual water height when possible. Manufacturer-listed tank dimensions can include glass thickness and may represent the tank's nominal capacity rather than the amount of water it actually contains.
For accurate calculations, use the aquarium volume calculator.
Essential aquarium constants.
How to plan an aquarium setup without guessing.
Start with real volume
Every other number — stocking, weight, heater size, filter flow — depends on how much water your tank actually holds, not the number printed on the box. Measure the interior glass, pick your shape, and use the tank volume calculator to get gross and net volume. If you're comparing tanks in litres and gallons, the liters ↔ gallons converter handles the conversion including UK imperial gallons.
Size the structure and equipment
Water is surprisingly heavy at 8.34 pounds per US gallon. A filled 55 gallon commonly exceeds 600 pounds once glass, substrate, and stand are included, so check your floor and stand before filling. Then size the heater and filter flow against the real volume, not the label. Substrate depth comes next — the substrate calculator converts footprint and bed depth into the bags you'll actually carry home.
Stock conservatively
The one-inch-per-gallon rule is a rough ceiling, not a target. Plan around adult sizes, group minimums, and how much maintenance you'll actually do. The stocking calculator turns your net volume and filter turnover into a bioload estimate, and the stocking guide gives realistic plans for 10, 20, 30, and 55 gallon community tanks. For planted tanks, read the CO₂ injection guide before you buy a regulator.
Built on standard aquatic chemistry benchmarks.
AquaTankCalc uses transparent formulas, standard aquarium conversions, and practical planning guidelines to make each calculation easy to understand and apply :
- 01/ Water Density: 8.34 lbs / US Gal (1.00 kg/L at 25°C)
- 02/ CO₂ Equilibrium: pH - log10(dKH) Henderson-Hasselbalch
- 03/ Substrate Density: ~1.4 - 1.6 kg/L for Aqua-Soil & Sand
// Recommended Planted Tank CO2 Targets (Target = 30 PPM) { "dKH_1.0": { "pH_6.0": "30 ppm (OPTIMAL)", "pH_6.4": "12 ppm (LOW)" }, "dKH_4.0": { "pH_6.6": "30 ppm (OPTIMAL)", "pH_7.0": "12 ppm (LOW)" }, "dKH_8.0": { "pH_6.9": "30 ppm (OPTIMAL)", "pH_7.3": "12 ppm (LOW)" } }
Frequently Asked Questions About Aquarium Volume
Common questions about calculating fish tank capacity, converting units, and measuring actual water volume.