Fish Tank Volume Calculator
Free fish tank volume calculator for rectangular, bow front, and cylinder tanks. Get gallons and liters instantly.
Calculate aquarium volume in gallons and litres for rectangular, bowfront, and cylinder tanks. Perfect for determining medication doses and equipment needs.
Tank Volume Tips
- • Measure the inside dimensions for most accurate results
- • For rimless tanks, measure to the actual water line
- • Bowfront tanks have a curved front panel that adds volume
- • Consider displacement from substrate (typically 1-2 inches deep)
- • Large rocks and driftwood can displace significant water volume
How do I calculate aquarium volume?
For rectangular tanks: Length × Width × Height ÷ 231 = Gallons
Quick Reference
Knowing your aquarium's exact water volume is crucial for proper medication dosing, determining filtration requirements, calculating stocking levels, and choosing the right equipment. Our aquarium volume calculator supports rectangular, bow front, and cylindrical tanks.
Measure Your Tank
Use a tape measure to get the length, width, and height of your aquarium. Measure from the inside edges for accuracy. For bow front tanks, also measure the bow depth at the center.
Select Tank Shape
Choose between rectangular (standard), bow front (curved front), or cylinder shapes. Each shape uses a different calculation formula.
Enter Measurements
Input your measurements in either inches or centimeters. The calculator automatically converts between units and provides results in both gallons and liters.
Account for Displacement
Remember that substrate, decorations, and equipment reduce actual water volume by 10-15%. Consider this when dosing medications or planning livestock.
10 Gallon
20" × 10" × 12"
Nano tank, good for bettas
20 Gallon Long
30" × 12" × 12"
Great for bottom dwellers
29 Gallon
30" × 12" × 18"
Popular community tank
40 Gallon Breeder
36" × 18" × 16"
Excellent footprint
55 Gallon
48" × 13" × 21"
Classic large tank
75 Gallon
48" × 18" × 21"
Show tank size
125 Gallon
72" × 18" × 21"
Large fish compatible
Why it matters: Overestimating water volume by 10-20%, leading to medication overdose
Do this instead: Always measure from the inside edges of the glass, accounting for glass thickness
Why it matters: Actual water volume is 10-15% less than calculated
Do this instead: Subtract displacement volume or use 85% of calculated volume for dosing
Why it matters: Water overflow when adding hands or equipment
Do this instead: Leave 1-2 inches of space at the top for safety
Why it matters: Incorrect dosing and equipment sizing
Do this instead: Always calculate actual water volume, not nominal tank size
Pro tip: Taking time to measure accurately and understand these common pitfalls will save you money on equipment, prevent fish losses, and create a healthier aquatic environment. When in doubt, double-check your measurements!
Recommended Products:
Available Services:
FishStores.org helps you find local aquarium shops with the products and expertise you need. Our directory includes over 5,000 fish stores across the United States.
Frequently Asked Questions
How to calculate volume of water tank?
For rectangular tanks: multiply length x width x height. For cylinders: π x radius² x height. For bow fronts: use our specialized calculator that accounts for the curved front. All measurements should be internal dimensions.
How do I calculate gallons in my water tank?
Measure internal dimensions in inches, multiply length x width x height, then divide by 231 (cubic inches per gallon). Our calculator does this automatically and handles different tank shapes.
How many gallons is a 24x24x48 tank?
A 24x24x48 inch tank holds approximately 120 gallons when completely full. However, actual water volume is typically 100-105 gallons after accounting for substrate, decorations, and not filling to the brim.
What's the difference between actual and advertised tank volume?
Advertised volume assumes filling to the very top. Actual water volume is 10-15% less due to substrate (2-3 inches), decorations, equipment, and leaving space at the top to prevent overflow.
How do I measure a bowfront aquarium?
Measure length and height normally. For bow depth, measure from the center of the curved front to the back glass. Our calculator uses the bow measurement to accurately calculate the additional volume from the curve.
Why is knowing exact tank volume critical?
Accurate volume ensures proper medication dosing (overdosing can be fatal), correct filter flow rates (8-10x turnover per hour), appropriate heater wattage (3-5 watts per gallon), and safe stocking levels.
Setting Up Your Tank?
After calculating volume, use these tools to complete your setup:
More Aquarium Calculators
All calculators are free to use and designed by aquarium experts. Browse all aquarium tools or find fish stores near you.
Related Topics
Learn how tank volume affects filter selection and flow rates
Explore aquarium filtration guide →How many fish can your tank safely hold?
Explore fish stocking calculator →Calculate weekly water change volumes for your tank
Explore water change calculator →Why Accurate Calculations Matter
Precise measurements are the foundation of successful aquarium keeping. Whether you're calculating water volume for medication dosing, determining substrate amounts for a planted tank, or sizing equipment like heaters and filters, accuracy prevents costly mistakes and ensures the health of your aquatic pets. Our calculators take the guesswork out of aquarium math, helping both beginners and experienced aquarists make informed decisions.