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Fish Tank Calculator — Minimum Tank Size + Stocking Density for 30+ Species

Fish tank size calculator — input fish species and count, get the minimum tank gallons/liters needed and stocking density warnings.

  • Runs locally
  • Category Calculator
  • Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.
The #1 myth in fishkeeping: a goldfish is NOT a 1-gallon-bowl fish. A common goldfish reaches 20 cm and needs at least 20 gallons (75 L) per fish. This tool uses per-species water-volume requirements from SeriouslyFish, AqAdvisor, and fishbase.org — not the rough "1 inch per gallon" rule.
Add fish species
Common Goldfish
Adult size (cm): 20Per fish (L): 75Temp (°C): 10–22pH: 6.5–8.5Temperament: PeacefulLifespan: 15 years
Adults exceed 20 cm — the 1-gallon bowl is the #1 myth.
Minimum tank
75liters·19.8US gallons
Stocking density
Comfortable
All species fit, parameters overlap, no conflicts.
Warnings
No warnings — this combination works.
Sources: SeriouslyFish, AqAdvisor, FishBase.org adult-size + tank-volume data.

What this tool does

Free fish tank size calculator that answers two questions every new aquarist asks at the pet store and nobody answers honestly: "how big a tank do I actually need?" and "how many fish can I keep in it?" Pick from 30+ common freshwater species — goldfish, guppy, neon tetra, corydoras, angelfish, discus, Malawi cichlids, betta, flowerhorn, silver arowana, koi, oscar, plecos, harlequin rasbora, kuhli loach, cherry shrimp, crystal shrimp, amano shrimp, ghost shrimp, apple snail and more. Each species carries adult size, per-fish water-volume requirement, temperature range, pH range, temperament, lifespan, and a note on what beginners get wrong. Add species and counts; the tool computes the minimum tank in liters and US gallons, scores stocking density as comfortable / tight / overstocked, and surfaces hard incompatibility warnings: temperature ranges that do not overlap, pH ranges that do not overlap, aggressive species mixed with peaceful ones, schooling fish kept below the minimum group size, and species-only fish that cannot be mixed at all (male bettas, rainbow sharks, flowerhorns, arowanas, redtail catfish). Volume data is compiled from SeriouslyFish, AqAdvisor, and FishBase.org — not the outdated "one inch per gallon" rule. 100% in your browser — no signup, no upload, instant calculation.

Tool details

Input
Numbers
The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output
Live result
The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy
Browser-side processing
The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share
No account required
Open the page and use it; whether results survive refresh depends on the tool.
Performance budget
Initial JS <= 22 KB
No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit
Calculator · Content Creator
Category and role tags drive related tools, internal links, and quick fit checks.

How to use

  1. 1. Input

    Paste or drop your content into the tool panel.

  2. 2. Process

    Click the button. All processing is local in your browser.

  3. 3. Copy / Download

    Copy the result or download to disk in one click.

How Fish Tank Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

  • Getting a realistic range before a purchase, plan, workout, or schedule decision.
  • Comparing scenarios by changing one input at a time.
  • Turning rough assumptions into a number you can discuss.

Calculation checks

  • Double-check units, dates, rates, and rounding assumptions.
  • Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
  • Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

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  2. 2 Paint Calculator Wall area → litres & cans of paint, with doors/windows deducted, coats and price — metric & US units, browser-only Open
  3. 3 Electricity Cost Calculator Power × hours × tariff → kWh and cost per day, month, and year — add multiple appliances, account for standby — browser-only. Open

Real-world use cases

  • New aquarist sizing the first tank before buying anything

    You walked into the pet store wanting "a goldfish and maybe a betta." Enter 2 common goldfish and 1 male betta. The tool flags the betta as solo-only and the goldfish needing 75 L plus 38 L, so you learn the real answer before spending a cent: the goldfish go in a 113 L tank, the betta in its own 19 L. Two tanks, not one bowl.

  • Planning a peaceful 60 L community for nano fish

    You have a 60 L tank and want a school. Enter 10 neon tetras and 6 corydoras. The verdict comes back comfortable, temperature overlaps at 22 to 26 C, both meet their group minimum of 6. Now add 1 angelfish to see what breaks: the tool warns the angelfish will eat full-grown neons and needs roughly 75 L on its own. You drop it.

  • Checking whether two cichlids can share a tank

    A friend offers you discus and you already keep Malawi cichlids. Enter both. The pH ranges do not overlap at all, Malawi want 7.8 to 8.6 and discus want 5.5 to 7.0, so the tool returns overstocked and incompatible on parameters alone. You keep them in separate setups instead of guessing a middle pH that stresses both species.

  • Stopping an impulse arowana buy at the store

    The silver arowana in the tank looks 15 cm and cute. Enter 1 arowana plus your existing 4 tetras. The tool flags it as solo-only and notes adults reach 90 to 100 cm and eat anything that fits in their mouth, including the tetras. It also shows the real tank floor is far past a 200 L home tank. You walk away before a 400 dollar mistake.

Common pitfalls

  • Counting only adult length, not waste load. Ten 3 cm neons and one 30 cm pleco have similar total length but the pleco produces far more waste, so it needs roughly 75 L while the neons share 60 L.

  • Buying schooling fish in pairs. Three neon tetras stay stressed and glass-surf, color fades within weeks. Enter 6 or more, the tool clears the group-size warning only at the real minimum.

  • Trusting a 24 C compromise for non-overlapping fish. Discus at pH 5.5 to 7.0 and Malawi at 7.8 to 8.6 share no pH at all, so the tool flags overstocked. Pick one biotope, not a middle value.

Privacy

Everything runs in your browser. The species you pick and the counts you enter are computed locally and never sent to a server, so there is no account and no upload. When you share a result link, your selected species and counts are encoded in the URL so the other person sees the same tank plan, which is the only place your inputs travel.

FAQ

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Made by Toolora · 100% client-side · Updated 2026-06-13