Aquarium Volume Calculator 🐠
Calculate the exact water volume of your fish tank in US gallons, Imperial gallons, and liters. Perfect for aquarium setup, fish stocking decisions, water treatments, and filter sizing. Supports rectangular, cylindrical, hexagonal, bow front, and spherical tanks.
What Is an Aquarium Volume Calculator?
An aquarium volume calculator is a free online tool that computes the exact water volume of your fish tank based on its dimensions and shape. Knowing your aquarium's volume is essential for proper fish stocking, dosing medications, adding water conditioners, and selecting the right filter and heater.
Our calculator supports multiple tank shapes, rectangular, cylindrical, hexagonal, bow front, and spherical, and provides results in US gallons, Imperial gallons, and liters.
How Does the Aquarium Volume Calculator Work?
The calculator uses standard geometric formulas to compute the volume of your tank shape:
Rectangular Tank: Volume (in³) = Length × Width × Height
Cylindrical Tank: Volume (in³) = π × (Diameter/2)² × Height
Hexagonal Tank: Volume (in³) = (3√3/2) × Side² × Height
Bow Front Tank: Approx. volume = (Length × Width × Height) + (Length × Bow Depth × Height × 0.5)
Spherical Tank: Volume (in³) = (4/3) × π × (Diameter/2)³
Conversions: US Gallons = in³ ÷ 231 | Imperial Gallons = in³ ÷ 277.42 | Liters = in³ × 0.0163871
The calculator then converts cubic inches to US gallons, Imperial gallons, and liters using standard conversion factors. Advanced options let you account for substrate, decorations, and water level to calculate your actual water volume.
Why Use This Aquarium Volume Calculator?
- Multi-Shape Support: Handles rectangular, cylindrical, hexagonal, bow front, and spherical tanks.
- Multiple Units: Results in US gallons, Imperial gallons, and liters.
- Advanced Options: Account for substrate, decorations, and water level for accurate actual water volume.
- Free & Easy: No registration, no fees, just enter your dimensions and get results instantly.
- Mobile-Friendly: Use it on any device.
What Factors Affect Actual Water Volume?
- Substrate: Gravel, sand, and other substrates displace water. A 55-gallon tank with 2 inches of gravel may lose 3-5 gallons of water volume.
- Decorations: Rocks, driftwood, and ornaments take up space and reduce water volume.
- Water Level: Most tanks are filled to 90-95% of their height, not to the brim.
- Glass Thickness: The outside dimensions of a tank are larger than the inside water volume.
Always measure medications and conditioners based on your calculated water volume, not the tank's maximum capacity.
Fish Stocking Guidelines by Volume
- Freshwater Tropical: 1 inch of adult fish per US gallon
- Goldfish: 1 inch per 3 gallons (they produce more waste)
- Saltwater: 1 inch per 4-5 gallons (more sensitive ecosystem)
- Shrimp/Snail Tanks: 10-20 small shrimp per gallon
Equipment Sizing Guide
- Heater: 2.5-5 watts per gallon
- Filter: 4-6 times tank volume per hour (GPH)
- Lighting (planted): 2-5 watts per gallon
❓ Aquarium Volume FAQ
How do I calculate the volume of my rectangular aquarium?
Multiply the length, width, and height of your tank in inches: Volume (in³) = Length × Width × Height. Then divide by 231 to get US gallons.
What is the difference between US gallons and Imperial gallons?
A US gallon is 231 cubic inches, while an Imperial gallon (used in the UK and Canada) is 277.42 cubic inches. One US gallon is about 3.785 liters, and one Imperial gallon is about 4.546 liters.
How do I calculate the volume of a cylindrical aquarium?
Use the formula: Volume (in³) = π × (Diameter/2)² × Height. π ≈ 3.14159.
What is a bow front aquarium and how is its volume calculated?
A bow front aquarium has a curved front panel. Its volume is approximately: (Length × Width × Height) + (Length × Bow Depth × Height × 0.5). This treats the curved section as roughly half a cylinder.
How do I calculate the volume of a hexagonal tank?
Volume (in³) = (3√3/2) × Side² × Height. The area of a hexagon is approximately 2.598 × side².
How do I calculate the volume of a spherical aquarium?
Volume (in³) = (4/3) × π × (Diameter/2)³. Note that spherical aquariums are typically filled below the top.
Why is my actual water volume less than the tank's volume?
Substrate (gravel/sand), decorations, rocks, and driftwood all displace water. A heavily decorated 55-gallon tank may only hold 45-50 gallons of actual water.
How much water does substrate displace?
It depends on the depth and type of substrate. As a rough guide, 1 inch of gravel in a 48"×18" tank displaces about 3-4 gallons of water. The calculator allows you to enter substrate volume for a more accurate result.
What is the "inch per gallon" rule for fish stocking?
The rule suggests 1 inch of adult fish per gallon for freshwater tropical fish. However, this is a rough guideline, consider fish behavior, waste production, and swimming space. Goldfish need 1 inch per 3 gallons, and saltwater fish need 1 inch per 4-5 gallons.
How do I choose the right heater for my aquarium?
A general rule is 2.5-5 watts per gallon of water. For a 55-gallon tank, a 150-250 watt heater is typically sufficient. Consider room temperature and desired water temperature when sizing.
What filter flow rate do I need for my aquarium?
Your filter should turn over 4-6 times the tank volume per hour (GPH). For a 55-gallon tank, look for a filter rated at 220-330 GPH.
How do I convert gallons to liters?
1 US gallon = 3.785 liters. 1 Imperial gallon = 4.546 liters. The calculator provides both conversions automatically.
What are the most common aquarium sizes and their volumes?
Common sizes include: 10 gal (20"×10"×12"), 20 gal long (30"×12"×12"), 29 gal (30"×12"×18"), 55 gal (48"×13"×21"), 75 gal (48"×18"×21"), and 125 gal (72"×18"×21").
How much does aquarium water weigh?
Freshwater weighs approximately 8.34 pounds per US gallon. Saltwater is slightly heavier at about 8.55 pounds per gallon. A 55-gallon tank holds about 460 pounds of water.
Should I measure medications based on tank size or actual water volume?
Always measure medications and water conditioners based on your actual water volume, not the tank's maximum capacity. Overdosing can harm your fish.
How do I calculate the volume of an irregularly shaped tank?
For irregular shapes, you can fill the tank with water and measure the amount used, or break the shape into simpler geometric forms and sum their volumes. This calculator supports the most common aquarium shapes.
What is the difference between a "breeder" tank and a standard tank?
Breeder tanks are wider and shallower than standard tanks, providing more surface area for breeding. For example, a 40-gallon breeder is 36"×18"×16", while a standard 40-gallon is often 48"×13"×16".