# Aquarium Calculator

Calculate aquarium volume in gallons and liters for rectangular, bow-front, and cylindrical fish tanks. See total water weight and filled volume.

## What this calculates

Figure out exactly how much water your aquarium holds. Choose your tank shape, enter the dimensions, and get the volume in gallons and liters along with total water weight. Knowing your actual water volume is essential for dosing medications, fertilizers, and salt mixes.

## Inputs

- **Tank Shape** — options: Rectangular, Bow-Front, Cylindrical
- **Length** (inches) — min 0 — Front-to-back for bow-front tanks
- **Width** (inches) — min 0 — Side-to-side measurement (flat back for bow-front)
- **Height** (inches) — min 0
- **Bow Depth** (inches) — min 0 — Extra depth at the center of the bow (bow-front only)
- **Fill Level** (%) — min 0, max 100 — Tanks are typically filled to about 95% to prevent overflow

## Outputs

- **Volume**
- **Volume**
- **Volume**
- **Water Weight**
- **Water Weight**
- **Filled Volume**

## Details

Volume formulas by tank shape:

  - Rectangular: Length x Width x Height

  - Bow-front: Rectangular volume + the curved bow section (approximated as a half-ellipse)

  - Cylindrical: pi x radius^2 x Height

Useful conversions:

  - 1 cubic inch = 0.004329 US gallons

  - 1 US gallon = 3.785 liters

  - 1 gallon of freshwater weighs about 8.34 lbs (3.78 kg)

  - 1 gallon of saltwater weighs about 8.56 lbs (3.88 kg)

Why fill level matters: Most aquariums are only filled to 90-95% capacity. Substrate, decorations, and equipment displace water too, so your actual water volume is usually 10-15% less than the full tank volume. Keep this in mind when dosing chemicals.

## Frequently Asked Questions

**Q: How do I measure a bow-front aquarium?**

A: Measure the length (left to right), the width of the flat back panel, and the height. Then measure the bow depth, which is the extra distance the curved front glass extends beyond the flat back. This calculator uses these measurements to approximate the bow section volume.

**Q: Why does water weight matter for aquariums?**

A: Water is heavy. A 55-gallon tank weighs over 450 lbs when filled, not counting the tank, stand, substrate, and rocks. You need to make sure your floor and stand can handle the total weight, especially for tanks over 30 gallons.

**Q: How much substrate displaces water volume?**

A: A typical 2-inch gravel bed in a standard aquarium displaces about 5-10% of the tank volume. Planted tanks with thicker substrate layers may displace even more. Subtract this when calculating doses for medications or treatments.

**Q: What size aquarium do I need for my fish?**

A: A common guideline is 1 inch of fish per gallon for small community fish, but this varies widely. Active swimmers need more space, and larger fish need much more. Research the specific species you plan to keep for proper tank size recommendations.

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Source: https://vastcalc.com/calculators/everyday/aquarium-volume
Category: Everyday Life
Last updated: 2026-04-08