Fish Tank Size Calculator

Calculate the perfect tank size for your aquarium and ensure a healthy environment for your fish

Calculator Mode

Default Mode is perfect for beginners who want a quick estimate of their tank's stocking level.

Shape
Units
Dimensions
cm
Decor & Substrate Density
Total Volume 0 Liters
Usable Volume 0 Liters90% usable
L | 0 cm
H | 0 cm
W | 0 cm

Default Mode: Fish Groups

Aquarium Analysis

Usable Tank Volume
0 L
Estimated Volume Needed
0 L
Tank Load:

🫧 Very Low - Plenty of space left! Add more fish if you like.

0%

Very Light

Minimal bioload 🫧 Just 10–15% water change weekly keeps your tank fresh and stress-free.

Fish Tank Size & Stocking Calculator: Smart, Science-Based & Beginner Friendly

Whether you're setting up your first 20L betta bowl or designing a planted community tank, planning matters β€” and that's where this tool comes in. Our Fish Tank Size and Stocking Calculator was built for both newcomers and veteran aquarists to help answer the most common (and most crucial) question: "How many fish can I keep?"

Why This Calculator Was Created

Overcrowded tanks are one of the most common mistakes in fishkeeping, especially for beginners. Too many fish lead to high waste production, ammonia spikes, stress, and ultimately disease or death.

  • Beginner-friendly planner that feels approachable and easy to use
  • Science-based tool that factors in fish size, waste output, and tank layout
  • Flexible experience with both simple and advanced options
  • Clean UI that delivers actionable insights, not just raw numbers

The result? A tool that helps you stock your tank safely, maintain balance, and enjoy the hobby more.

Key Features
  • Default Mode (Beginner-Friendly): Choose fish by size, add quantity, get visual feedback & maintenance tips.
  • Expert Mode (Advanced): Select from 200+ species, customize bioload, and build detailed plans.
  • Bioload Feedback System: Get bioload tier, water change advice, and clear tooltips/icons.
  • Tank Volume Calculator: Supports rectangle/cylinder tanks, metric/imperial, and usable volume adjustment.
How the Math Works (Under the Hood)
  1. Volume Calculation: Rectangle = L Γ— W Γ— H; Cylinder = Ο€ Γ— (RΒ²) Γ— H; Usable = minus % for dΓ©cor, etc.
  2. Default Mode Stocking: Total Fish Length = Qty Γ— Avg Size; 1L per cm of fish.
  3. Expert Mode Stocking: Bioload = Qty Γ— Avg Size Γ— Bioload Factor; sum for all species.
  4. Tank Load Indicator: Load % = (Required / Usable) Γ— 100; Tiers: Very Light to Overstocked.
Glossary of Aquarium Terms
  • Bioload β€” How much waste (poop, ammonia, organics) a fish produces. Bigger fish or messy eaters have higher bioloads.
  • Stocking Level β€” A measure of how full your tank is, factoring in both size and fish waste output.
  • Usable Volume β€” The actual amount of free water after accounting for decorations, filters, gravel, etc.
  • Bioload Factor β€” A multiplier (e.g. 0.8–2.5) estimating how "messy" a fish is compared to average.
  • Tank Load β€” The strain your aquarium is under. Higher load means more frequent cleaning and filtration needs.
  • Schooling Requirement β€” Minimum group size needed to keep social fish healthy and stress-free.
  • Maintenance Tier β€” Our advice for how often you should clean or change water, based on the overall load.

Disclaimer

This calculator provides guidance based on general aquarium science, expert consensus, and best practices β€” but it is still just a tool.

  • Real-world conditions vary (filtration, feeding, water chemistry)
  • Always research individual species behavior and compatibility
  • Bioload and volume estimations are not absolute; they are suggestions to help guide safe and ethical stocking decisions

When in doubt: understock, overfilter, and observe. Healthy fish are active, alert, and swimming in clean water.

Final Thoughts

Fishkeeping is a mix of science, patience, and care. With this calculator, we hope to simplify the science part so you can focus on what matters most β€” creating a peaceful, thriving underwater world. πŸŸπŸ’§

Built with ❀️ for aquarists of all levels.