What is a Fish Tank Volume Calculator?
A fish tank volume calculator helps aquarists measure the gross and net water capacity of rectangular, bowfront, or cylinder aquariums to maintain healthy aquatic environments for fish and corals.
Learn more about aquarium sizing and capacity in the Aqueon Choosing the Right Aquarium guide.
Aquarium Volume Formulas
Rectangular Aquarium (Inches to US Gallons):
Volume (US Gal) = (Length × Width × Height in inches) / 231
Metric Aquarium (Centimeters to Litres):
Volume (Litres) = (Length × Width × Height in cm) / 1,000
How to Calculate Aquarium Volume
- Measure Tank Dimensions: Measure internal length, width, and height in inches or cm.
- Calculate Gross Volume: Apply the formula to find total gross volume.
- Deduct Substrate & Aquascaping: Subtract 10% to 15% for gravel, sand, and rock displacement.
- Establish Net Water Volume: Use net volume for water conditioner and medicine dosing.
Aquarium Sizing Walkthrough
For a standard 55-gallon rectangular aquarium measuring 48 inches long, 13 inches wide, and 21 inches high:
Gross Volume = (48 × 13 × 21) / 231 = 13,104 / 231 ≈ 56.73 US GallonsNet Water Volume (after 10% substrate displacement) = 56.73 × 0.90 ≈ 51.05 US Gallons
Standard Aquarium Size & Capacity Reference Table
| Aquarium Model | Dimensions (Inches: L × W × H) | US Gallons | Litres |
|---|---|---|---|
| 10 Gallon Standard | 20" × 10" × 12" | 10 gal | 38 L |
| 20 Gallon Long | 30" × 12" × 12" | 20 gal | 75 L |
| 29 Gallon Standard | 30" × 12" × 18" | 29 gal | 110 L |
| 55 Gallon Standard | 48" × 13" × 21" | 55 gal | 208 L |
| 75 Gallon Aquarium | 48" × 18" × 21" | 75 gal | 284 L |
| 120 Gallon Extra Large | 48" × 24" × 24" | 120 gal | 454 L |
Substrate Displacement & Water Weight Safety
Water weighs 8.34 lbs per gallon (1 kg per litre). A filled 55-gallon tank with substrate weighs over 600 lbs (270 kg). Ensure your aquarium stand is level and structurally rated for heavy static loads.