Aquarium inputs
Calculated results
Net water volume
0 L
0 US gal
Surface area
0 m²
0 ft²
Total system volume
0 L
0 US gal
Estimated safe system weight
0 kg
0 lb
| Parameter | Value |
|---|---|
| Tank shape | - |
| Measurement system | - |
| Internal water volume (liters) | 0 |
| Internal water volume (US gallons) | 0 |
| Surface area (square meters) | 0 |
| Surface area (square feet) | 0 |
| Total system volume (liters) | 0 |
| Total system volume (US gallons) | 0 |
| Safe system weight (kg) | 0 |
| Safe system weight (lb) | 0 |
| Approximate floor load (kg/m²) | 0 |
| Approximate floor load (lb/ft²) | 0 |
| Community rule: small freshwater fish length | 0 |
| Cautious stocking: reduced total fish length | 0 |
| Estimated fish count (chosen profile) | 0 |
| Assumed rule for chosen profile | - |
Choosing the right aquarium size
Tank size affects water stability, stocking flexibility, and maintenance effort. Larger volumes dilute waste better and offer more swimming space, but require more space, stronger stands, and higher initial budgets for glass, substrate, and equipment.
Room size and viewing distance
Match aquarium length to the main viewing distance so fish remain clearly visible. Avoid tanks that block doors, windows, or access paths. Check that doors, lifts, and staircases can physically accommodate the tank and stand dimensions.
Balancing bioload and filtration capacity
Bioload is the total waste produced by fish, plants, and feeding. Higher bioload demands stronger filtration and more frequent maintenance. This calculator estimates conservative stocking limits so you can choose filters and water-change schedules that match realistic bioload for your planned community.
Matching filter flow to volume
Many freshwater setups target 4–8 system turnovers per hour. Use the calculated total system volume to size hang-on-back, canister, or sump return pumps. Account for head height losses, pre-filters, and flow restrictions from hard plumbing or spray bars.
Assessing stand strength and floor loading
Water, glass, rock, and substrate together create a dense point load. The system weight and floor load estimates help you judge whether lightweight furniture is unsuitable and when you should use purpose-built stands or consult a structural professional, especially in older buildings.
Positioning tanks safely
Where possible, place aquariums along load-bearing walls and spread weight using full-contact stands or foam mats. Avoid concentrating large systems over unsupported spans, flexible floors, or near vibration sources such as heavy doors and frequently used treadmills.
Estimating energy and running costs
Lighting, filtration, and heating draw continuous power. After you know system volume, you can approximate heater wattage and light requirements, then combine them with local electricity prices using tools such as the Electricity Cost Calculator to estimate monthly operating costs.
Lighting schedules and dimming
Shortening photoperiods, using dimmers, and choosing efficient LEDs all reduce running costs and excess algae growth. Plan your light output around plant species, viewing preferences, and typical daily occupancy of the room where the aquarium sits.
Planning water changes and usage
Regular water changes export nitrate and dissolved organics. By combining system volume with your chosen change percentage, you can estimate weekly water use, schedule refills, and understand impacts on your water bill and filtration needs for tap conditioning.
Linking water use with household habits
You can compare aquarium water use with showers, laundry, and dishwashing using tools such as the Water Usage Calculator, helping you adjust maintenance days around other high-demand household activities.
Integrating this calculator into your planning
Treat the results as a planning baseline. Combine tank volume, stocking estimates, and floor loading with species research, aquascape sketches, and budget lists. Update inputs whenever you adjust dimensions, sump size, or decor layout during design.
Saving and comparing scenarios
Use the CSV download to archive different tank concepts and the PDF export for quick reference on mobile devices. Keeping multiple scenarios makes it easier to compare upgrade paths, location options, and ongoing costs before committing to a final build.
Formulas used in this aquarium size calculator
This tool estimates internal water volume by converting your dimensions into cubic units, applying fill level, subtracting substrate volume, and reducing space displaced by decor and equipment.
-
Rectangular tank volume: V = L × W × Hwater
Hwater = (H × fillLevel) − substrateDepth - Cylindrical tank volume: V = π × (D/2)2 × Hwater
- Decor displacement: Vnet = V × (1 − decorPercent / 100)
-
Unit conversions:
1 inch = 2.54 cm
1 liter = 1000 cm³
1 US gallon ≈ 3.78541 liters -
Surface area for gas exchange:
Rectangular: A = L × W
Cylindrical: A = π × (D/2)2 -
Stocking guidelines (approximate and conservative):
Freshwater community: about 1 cm fish length per liter
Imperial equivalent: about 1 inch fish length per US gallon -
System volume and weight:
TotalVolume = TankVolume + ExtraWater
WaterWeight ≈ TotalVolume (kg)
SafeWeight = (WaterWeight + ExtraSolidWeight) × SafetyFactor
These guidelines are simplified. Always consider filtration, species aggression, maintenance habits, and real adult sizes when deciding final stocking levels for an aquarium.
How to use this aquarium size calculator
- Choose your preferred measurement system. Metric uses centimeters and liters, while imperial uses inches and US gallons for all calculations.
- Select your tank shape. Standard glass aquariums are usually rectangular, while columns and barrels are more similar to cylindrical tanks.
- Enter external tank length, width, and height or diameter and height for round tanks. Use measurements close to inside glass dimensions where possible.
- Adjust the fill level percentage to reflect how high you actually fill the tank. Lower levels reduce net water volume and stocking capacity.
- Add expected substrate depth at the bottom and an approximate decor displacement percentage for rocks, driftwood, equipment, and background materials.
- Enter an average adult fish length and choose a stocking profile that best matches your plan, such as community freshwater, goldfish, or marine reef setups.
- If you use a sump or external filter, enter its approximate water volume, plus an estimate of substrate and decor weight to see weight and load.
- Pick a safety factor to build margin into the structural load, then press “Calculate aquarium size” to update all system estimates and exports.
Example aquarium sizes and capacities
The table below shows a few typical rectangular tanks with approximate volumes and community stocking guidelines, assuming moderate filtration and regular maintenance.
| Tank label | Dimensions (L × W × H cm) | Approx. volume (liters) | Approx. volume (US gallons) | Suggested community fish length |
|---|---|---|---|---|
| Small desktop tank | 45 × 25 × 30 | ~27 | ~7 | 20–25 cm total small fish |
| Standard 60 cm tank | 60 × 30 × 35 | ~54 | ~14 | 45–55 cm total small fish |
| Popular 90 cm community tank | 90 × 40 × 45 | ~135 | ~36 | 110–130 cm total small fish |
| Large display aquarium | 120 × 45 × 50 | ~216 | ~57 | 170–200 cm total small fish |
These examples assume similar substrate and decor levels to the calculator defaults. Heavier aquascaping or large territorial species may require lighter stocking than shown.
Frequently asked questions
Is a longer aquarium better than a taller aquarium?
Yes, most fish benefit more from horizontal swimming space than height. Longer tanks provide better gas exchange, more territories, and easier aquascaping, especially for active schooling fish and bottom dwellers that prefer floor area.
Can I exceed the suggested stocking level if filtration is strong?
You can, but it adds risk. Strong filtration helps, yet crowding still increases stress, aggression, and oxygen demand. Use this calculator’s stocking guidance as a conservative limit, especially while you are learning maintenance routines.
How accurate are the floor load and weight estimates?
They are planning estimates, not engineering guarantees. Glass thickness, stand design, and building structure all matter. For very large systems, check local building codes or consult an engineer before placing heavy tanks on suspended floors.
Do I size the heater and filter from tank volume or system volume?
Always use total system volume: display tank plus sump and large external filters. This calculator reports both tank and system volume so you can select heaters, filters, and circulation pumps that match your complete water volume.
How do aquarium water changes affect my utility bills?
Water changes add up over time. Combine system volume and your change schedule with household tools such as the Water Usage Calculator to understand total monthly consumption and adjust frequency if needed.
Can I reuse this calculator when upgrading to a larger tank?
Yes. Simply enter the new dimensions, substrate depth, and sump volume. Export CSV for old and new setups, then compare water volume, weight, and stocking capacity to plan budget, equipment reuse, and livestock transfers.
What if my tank shape is irregular or custom built?
Choose the closest standard shape and slightly underestimate dimensions to stay conservative. For complex designs, divide the tank into simple sections, calculate each volume separately, and combine totals before entering values here.