Fish Tank Size Calculator – Find the Perfect Aquarium Size for Your Fish Instantly

Fish Tank Size Calculator

Estimate aquarium volume and recommended tank size fast — convert dimensions to gallons & liters and get stocking guidance.

Input Parameters (Dimensions)

Tip: Use inside dimensions (water level) for the most accurate result. 1 US gallon = 231 cubic inches.

Input Parameters (Stocking Recommendation)

Note: This rule-of-thumb uses 1 gallon per 1 inch of fish as a baseline. Adjust up for messy or territorial species.

Result

How to Use Fish Tank Size Calculator?

1. Choose the calculator tab: Dimensions → Volume to convert tank measurements to gallons and liters, or Fish Count → Recommendation to estimate recommended tank size based on the number and length of fish.
2. Enter values into the input fields (placeholders show examples).
3. Click the green button to calculate. Results and friendly messages will appear below. Use Clear to reset fields.

What is a Fish Tank Size Calculator?

A Fish Tank Size Calculator helps hobbyists and fish keepers determine aquarium volume (gallons & liters) from length/width/height, and recommends an appropriate tank size for your fish count using common stocking rules. It's great for planning purchases, choosing filters, and ensuring healthy stocking levels.

How Fish Tank Size Calculator Works?

It uses straightforward math and aquarium best-practice rules:

• Formula (dimensions → gallons): gallons = (length_in × width_in × height_in) / 231
• Liters: liters = gallons × 3.78541
• Stocking rule: baseline 1 gallon per 1 inch of fish, then adjust by species, adult size, and filtration.

Purpose of Fish Tank Size Calculator

The main purpose is to remove guesswork: quickly estimate aquarium volume, choose the right filter/heater, determine suitable fish load, and avoid overcrowding — which improves fish health and water quality.

Examples of Fish Tank Size Calculator

• Input: 36" × 12" × 18" → Result: ~33.6 gallons (127.3 liters)
• Input: 24" × 12" × 16" → Result: ~19.9 gallons (75.3 liters)
• Stocking: 5 fish averaging 2" → Baseline need = 5 × 2 = 10 gallons (choose 10–20 gal tank depending on species)

Fish Tank Size Calculator Formula

Volume (in cubic inches) = length_in × width_in × height_in
US Gallons = cubic_inches ÷ 231
Liters = gallons × 3.78541

Tips for Fish Tank Size Calculator

• Measure inside dimensions (water level) for accuracy.
• Round up tank size to nearest common model (10, 20, 29, 55 gallons) for equipment compatibility.
• Consider adult fish size — always base stocking on adult length.
• Account for filter capacity and bioload: bigger tanks are more stable.

Benefits of Fish Tank Size Calculator

• Quickly converts measurements to gallons & liters.
• Provides stocking guidance to prevent overcrowding.
• Helps select tank, filter, and heater sizes.
• Useful for beginners and experienced hobbyists planning setups.

Frequently Asked Questions

The calculator is accurate when you use inside tank dimensions and measure in inches. It uses the standard conversion 1 US gallon = 231 cubic inches. For best results, measure the usable water height (not the total glass height).

It's a simple rule-of-thumb for small community fish, useful for initial planning. However, adjust upward for large, messy, or territorial species (cichlids, goldfish). Always consider adult size, not juvenile size.

Liters are useful if you live outside the U.S. The calculator automatically converts gallons to liters. Use the liters value to purchase supplies that use metric labels.

Convert cm to inches first (1 inch = 2.54 cm) and then enter values. You can also use an online converter then paste inches into the calculator for accurate gallons calculation.

Tanks, filters, and lids are sold in standard sizes (10, 20, 29, 55 gal). Rounding up helps you select compatible equipment and gives extra water volume for stability.

Yes — volume calculations are the same for freshwater and saltwater. Stocking guidance differs for marine species, so pair this tool with species-specific research.