Aquarium Volume Calculator (Gallons & Liters)

Calculate the water volume of your fish tank in US Gallons, UK Gallons, and Liters. Supports Rectangle, Cube, Cylinder, Bowfront, and Hexagon shapes.

1Tank Dimensions

Length (inch)

Width (inch)

Height (inch)

2Adjustments

Filled Percentage90%

Most tanks are not filled to the brim, and gravel/decor takes up space. 85-90% is a safe estimate.

Estimated Water Volume

17.95US Gal

Metric Volume

68 Liters

UK Volume

14.95 UK Gal

Total Weight (Approx)

~149.7 lbs / ~68 kg

Recommended Heater

75 Watts

Based on ~4-5 watts per gallon

Filter Flow Rate

72-108 GPH

Target 4-6x turnover per hour

Understanding Aquarium Water Volume

Knowing the exact water volume of your aquarium is critical for maintaining a healthy aquatic environment. It's not just about knowing how much water fits in the tank, but also about dosing medication, water conditioners, and fertilizers accurately.

Why 'Actual' Volume Matters

Most manufacturers list the "nominal" volume of the tank (e.g., a "20 Gallon" tank). However, this calculation assumes the tank is an empty glass box filled to the very brim. In reality, you lose volume to:

Glass Thickness: Internal dimensions are smaller than external ones.
Substrate: A 2-inch layer of gravel can displace 10-15% of water.
Decorations: Rocks, driftwood, and filters take up space.
Water Level: You rarely fill water to the absolute top edge.

Use the "Filled Percentage" slider in our calculator to account for these factors. A safe estimate for a decorated tank is usually 85-90% of the mathematical volume.

Why "Gallon" matters?

Many medications and water conditioners are dosed by US Gallons. Knowing your exact water volume prevents overdosing. Remember that substrate (gravel/sand) can reduce actual water volume by 10-20%.

Stocking Guide

A common rule of thumb is "1 inch of fish per gallon", but this is outdated. Surface area (Length × Width) is often more important for oxygen exchange than total volume.

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Frequently Asked Questions

How do I calculate the volume of my aquarium?

Measure the internal Length, Width, and Height of your tank. For a rectangular tank, multiply Length × Width × Height to get cubic inches or cm, then convert to gallons (1 gallon ≈ 231 cubic inches).

Is US Gallon different from UK Gallon?

Yes. 1 US Gallon is approximately 3.785 liters, while 1 UK (Imperial) Gallon is about 4.546 liters. Our calculator provides both for accuracy.

Does the substrate affect the water volume?

Yes! Gravel, sand, and decorations displace water. The actual water volume is usually 10-15% less than the total tank volume. Use our 'filled percentage' or estimate margin to account for this.

Understanding Aquarium Water Volume

Why 'Actual' Volume Matters

Glass Thickness: Internal dimensions are smaller than external ones.
Substrate: A 2-inch layer of gravel can displace 10-15% of water.
Decorations: Rocks, driftwood, and filters take up space.
Water Level: You rarely fill water to the absolute top edge.

Use the "Filled Percentage" slider in our calculator to account for these factors. A safe estimate for a decorated tank is usually 85-90% of the mathematical volume.

Aquarium Volume Calculator (Gallons & Liters)

1Tank Dimensions

2Adjustments

Estimated Water Volume

Recommended Heater

Filter Flow Rate

Understanding Aquarium Water Volume

Why 'Actual' Volume Matters

Why "Gallon" matters?

Stocking Guide

Frequently Asked Questions

How do I calculate the volume of my aquarium?

Is US Gallon different from UK Gallon?

Does the substrate affect the water volume?

More Aquarium Tools

Bowfront Aquarium Volume Calculator

Cylinder Aquarium Volume Calculator

Hexagon Aquarium Volume Calculator

Cube Aquarium Volume Calculator

Aquarium Volume Calculator (Gallons & Liters)

1Tank Dimensions

2Adjustments

Estimated Water Volume

Recommended Heater

Filter Flow Rate

Understanding Aquarium Water Volume

Why 'Actual' Volume Matters

Why "Gallon" matters?

Stocking Guide