Aquarium Size Calculator

Bow front aquariums have a curved front panel, making the capacity calculation slightly complex. A simple way to estimate is to use the Rectangular shape in our calculator: take a measurement of the length, the height, and find the average width (measure the width at the edge, measure it at the center peak, add them together, and divide by two). Entering these dimensions will give you a very close approximation.

Yes. Manufacturers usually list the "gross" volume based on the outside dimensions of the glass. If you have a tank with thick glass (or acrylic), the inside capacity in liters or gallons is actually smaller. For the most accurate calculation of your actual water volume, always measure the inside dimensions of the tank.

As a rule of thumb, subtract about 10% to 15% from your calculated gross volume to account for substrate, rocks, driftwood, and other hardscape elements in your setup. This also accounts for the fact that you don't fill the water to the very brim of the glass.

Yes, due to dissolved salts. Freshwater weighs approximately 8.34 pounds per US gallon (or roughly 1 kg per liter). Saltwater (depending on salinity or specific gravity) weighs about 8.55 pounds per gallon—roughly 2.5% heavier.

The "one inch of adult fish per gallon of water" is a classic beginner guideline used for stocking planning. While useful for small, slender fish like neon tetras, it falls apart for thick-bodied fish, high waste producers (like goldfish or cichlids), or active swimmers. Proper stocking also heavily depends on your filtration system's efficiency. Always research the specific bioload, adult size, and footprint requirements of each species.

It is standard practice to leave about 1 to 2 inches of space between the water surface and the top rim of the tank. This prevents accidental spills, allows room for surface agitation (essential for oxygen exchange), and gives jumping fish a buffer before hitting the lid.

Yes. Every piece of driftwood, large rock, and layer of substrate displaces water. A heavily aquascaped 20-gallon setup might only hold 15 to 16 gallons of actual water. This is why you should always dose medications or water conditioners conservatively based on estimated net water volume.

Manufacturers often round tank size figures to the nearest standard number for marketing (e.g., a "55-gallon" tank might actually hold 53 gallons). Furthermore, manufacturers usually base their numbers on the outside dimensions of the tank, which includes the thickness of the glass, leading to a slightly higher gross volume than its actual, usable capacity.