How do I calculate aquarium gallons?

Multiply the interior length × width × height in inches, then divide by 231 (cubic inches per gallon). This calculator does that automatically.

What wattage heater do I need?

A general rule is 3–5 watts per gallon of water. This calculator uses 4 W/gallon as a midpoint estimate. For cold rooms, use 5 W/gallon.

What size filter do I need for my tank?

Your filter should turn over the tank volume at least 4 times per hour. A 55-gallon tank needs a filter rated at 220+ GPH.

How many fish can I keep?

The classic rule is 1 inch of fish per gallon of water. This is a rough guide — actual stocking depends on filtration, species, and aquascape.

How much does a full fish tank weigh?

Water weighs about 8.34 lbs per gallon. A 55-gallon tank with water, gravel, and glass can weigh 600–700 lbs total.

Aquarium Volume Calculator

Calculate your aquarium volume in gallons and liters, water weight, heater wattage, filter GPH, and fish stocking capacity.

Length (inches) ?

Width (inches) ?

Height (inches) ?

Tank Shape

Volume (Gallons)

—

Volume (Liters) —

Water Weight (lbs) —

Extended More scenarios, charts & detailed breakdown ▾

Length (in)

Width (in)

Height (in)

Gallons

—

Liters —

Water Weight —

Professional Full parameters & maximum detail ▾

Tank Volume (gallons)

gal

Gravel Depth (inches)

Tank Footprint Length (in)

Tank Footprint Width (in)

Electricity Cost ($/kWh)

Volume

Substrate Displacement —

Effective Water Volume —

Equipment

Heater Wattage Needed —

Filter GPH Needed —

Heater Monthly Cost (est.) —

Stocking & Maintenance

Fish Stocking (inches of fish) —

25% Water Change Volume —

How to Use This Calculator

Enter your tank's interior dimensions in inches (length, width, height).
Select the tank shape (rectangle or bow front).
View volume in gallons and liters plus the total water weight.
Use the Cylinder Tank tab for round tanks.
Use the Partial Fill tab if the tank is not filled to the top.
The Professional tier calculates effective volume after gravel displacement, plus heater and filter recommendations.

Formula

Volume (gal) = Length (in) × Width (in) × Height (in) ÷ 231

Cylinder: π × r² × Height ÷ 231

Water Weight: gallons × 8.34 lbs/gal

Example

Example: Standard 55-gallon tank (48" × 13" × 21"): 48 × 13 × 21 ÷ 231 = 56.7 gallons (slight overage due to nominal sizing). Water weight ≈ 473 lbs.

Frequently Asked Questions

Multiply the interior length × width × height in inches, then divide by 231 (cubic inches per gallon). This calculator does that automatically.
A general rule is 3–5 watts per gallon of water. This calculator uses 4 W/gallon as a midpoint estimate. For cold rooms, use 5 W/gallon.
Your filter should turn over the tank volume at least 4 times per hour. A 55-gallon tank needs a filter rated at 220+ GPH.
The classic rule is 1 inch of fish per gallon of water. This is a rough guide — actual stocking depends on filtration, species, and aquascape.
Water weighs about 8.34 lbs per gallon. A 55-gallon tank with water, gravel, and glass can weigh 600–700 lbs total.