Fish Tank Size Calculator
Rough tank-volume estimates from a simplified fish-length model; check species-specific care needs.
Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)
About this calculator
This page applies fixed fish-length and filter multipliers to produce rough tank-volume and turnover estimates. They are not stocking recommendations: adult size, species behavior, group needs, tank footprint, filtration, cycling and water quality all matter.
Worked example
calculated with the default values below
Small fish under 2 in 10 · Medium fish 2-4 in 6 · Large fish over 4 in 2 · Fish type Tropical community · Bottom dwellers (cory, pleco) 3 Model bioload score (unitless) 46 in · Rough model lower estimate 46 gal · Rough model estimate (×1.3) 60 gal · Illustrative filter turnover 239 gal/h · Note Cycle the tank before adding fish, and stock gradually over several weeks
Method and assumptions
L = s + 3m + 6g + 2b; Grec = 1.3 × f × L This uses arbitrary category weights and gallon multipliers as a rough heuristic, not a husbandry guideline. The bioload score is unitless; results omit adult size, behavior, tank footprint, filtration capacity and water quality. This page applies fixed fish-length and filter multipliers to produce rough tank-volume and turnover estimates. They are not stocking recommendations: adult size, species behavior, group needs, tank footprint, filtration, cycling and water quality all matter. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Data sources
The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
Disclaimer
These calculators offer general guidance and do not replace veterinary advice. Individual animals vary with breed, weight, health status and medication. Suspected poisoning from chocolate, medication, plants or chemicals is an emergency — contact your veterinarian or a pet poison control service immediately rather than relying on a calculator.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
L = s + 3m + 6g + 2b; Grec = 1.3 × f × L
- s
- small fish count
- m
- medium fish count
- g
- large fish count
- b
- bottom-dweller count
- L
- unitless model bioload score
- Grec
- rough model gallon estimate
This uses arbitrary category weights and gallon multipliers as a rough heuristic, not a husbandry guideline. The bioload score is unitless; results omit adult size, behavior, tank footprint, filtration capacity and water quality.
Frequently asked questions
Is the recommended tank size a stocking recommendation?
No. These figures come from fixed fish-length multipliers, a 1.3 factor and a turnover estimate. The model does not account for adult size, behavior, schooling, territory, filtration capacity, cycling or water quality. Check species-specific husbandry guidance before choosing a tank.
Which inputs and limits apply to Fish Tank Size Calculator?
Use the units shown beside each field. These are form limits, not recommended settings. Small fish under 2 in: 0–500; Medium fish 2-4 in: 0–200; Large fish over 4 in: 0–100; Bottom dwellers (cory, pleco): 0–100 L = s + 3m + 6g + 2b; Grec = 1.3 × f × L This uses arbitrary category weights and gallon multipliers as a rough heuristic, not a husbandry guideline. The bioload score is unitless; results omit adult size, behavior, tank footprint, filtration capacity and water quality. This page applies fixed fish-length and filter multipliers to produce rough tank-volume and turnover estimates. They are not stocking recommendations: adult size, species behavior, group needs, tank footprint, filtration, cycling and water quality all matter. The references provide context and limitations. They do not validate this page’s illustrative multipliers, lookup values or predictions.
What is a complete worked example for Small fish under 2 in = 10; Medium fish 2-4 in = 6?
Inputs: Small fish under 2 in = 10; Medium fish 2-4 in = 6; Large fish over 4 in = 2; Fish type = Tropical community; Bottom dwellers (cory, pleco) = 3. Calculation: L = s + 3m + 6g + 2b; Grec = 1.3 × f × L. Results: Model bioload score (unitless) = 46 in; Rough model lower estimate = 46 gal; Rough model estimate (×1.3) = 60 gal; Illustrative filter turnover = 239 gal/h; Note = Cycle the tank before adding fish, and stock gradually over several weeks.