Aquarium Volume Calculator | Size in Gallons or Liters
Instantly find your tank's precise size in gallons or liters. Accurate volume is the first step to a thriving aquatic ecosystem.
Calculated Volume
Gross vs. Net Estimate
VisualizerNet volume assumes ~15% displacement for substrate and decor.
Why Precision Matters
A healthy tank starts with knowing exactly how much water you have.
Safe Dosing
Medicines and conditioners are potent. Accurately knowing your volume prevents toxic overdoses or ineffective underdosing.
Stocking Logic
Your tank's biological capacity is limited by volume. Use this number to calculate stocking density and keep stress levels low.
Equipment Sizing
Heaters and filters are rated by gallonage. Matching equipment to your true volume ensures efficiency and stability.
Gross vs. Net Volume
The calculator provides the Gross Volume (empty tank). However, substrate, rocks, and decorations displace water. Most aquarists subtract 10-20% to find the Net Volume (actual water).
How to Use the Aquarium Volume Calculator
- Pick your unit: Toggle between inches and centimeters — every input and placeholder updates to match.
- Choose a tank shape: Rectangle, Cylinder, Bow-Front, or Hexagon. The input fields change to ask for exactly the measurements that shape needs.
- Enter your measurements: Type each dimension. The result updates instantly as you type — no submit button.
- Read the result: The main figure is your gross volume, shown in US gallons (or liters), with the alternate unit and UK gallons below. The chart compares gross volume against a net estimate.
Gross vs. Net Volume
The calculator reports gross volume — the capacity of an empty tank. In practice, substrate, rocks, driftwood, and decorations displace water, so the actual water volume (the net volume) is lower. Most aquarists subtract 10–20%; the chart uses a ~15% displacement estimate as a visual reference. Use net volume, not gross, when dosing medications or water conditioners, since dosing by the larger gross figure risks overdosing your tank.
Shape Formulas
Each shape uses a standard geometric volume formula. Rectangular tanks multiply length × width × height. Cylinders use π × radius² × height. Hexagonal tanks compute the regular-hexagon area from the flat-to-flat measurement, then multiply by height. Bow-front tanks combine a rectangular body with a circular-segment "bulge," calculated from the maximum and side widths. All results convert from cubic inches (231 in³ per US gallon) or cubic centimeters (1000 cm³ per liter), with 3.78541 liters per US gallon and 4.54609 liters per UK gallon.
Frequently Asked Questions
Why does the calculator show gross volume instead of net volume?
Gross volume is a fixed, measurable property of your tank; net volume depends on how much substrate and decor you add, which varies from setup to setup. The calculator gives you the reliable gross figure and a ~15% net estimate so you can adjust for your own aquascape.
Which volume should I use for dosing medications?
Always use net volume — the actual water in the tank. Dosing against the larger gross figure means you add more medication or conditioner than the water can safely carry, which risks overdosing sensitive fish and invertebrates.
How do I measure a bow-front tank?
You need four numbers: length, height, the maximum width (at the center of the curved front), and the side width (at the flat ends). The calculator adds the curved "bulge" to the rectangular body to get an accurate volume, rather than treating the tank as a plain rectangle.