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Aquarium Volume
Calculator

Get gross and net liters from your tank dimensions, subtract substrate, and calculate your water change amount – right here, no registration needed.

Dimensions & Settings
Inner dimensions
Substrate & decor deduction
Typically 15–25% for standard substrate. Heavily planted tanks are more like 25–30%.
Fill level
Typically 90–95% of height – leave room at the top for air exchange.
Water change
What percentage of the net volume you change.
Result
Enter your tank dimensions.
Help – understanding gross, net & deductions

Gross volume: length × width × height ÷ 1000. This is what's printed on the sales label – but no tank actually holds that much water in practice.

Net volume: gross minus substrate, rocks, decor and fill level. This figure is what matters for stocking density, dosing and water changes.

Substrate deduction: normal 5 cm gravel layer ≈ 15–20% deduction. Deep sand plus large rocks ≈ 25–30%. Lightly planted with little decor: 10–15%.

Water changes: 25–30% per week is a proven guideline. During cycling or with high stocking: 30–50%. Net volume × change % = liters of replacement water needed.

With a free account
Set up your tank once – volume always at hand.

Instead of recalculating every time: your tank dimensions and net volume are saved in your profile. Dosing amounts, water change volume and reminders are calculated automatically.

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Track water changes

Log every water change. Always see your history and last-change date at a glance. Reminders when it's been a while.

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Water parameter history

Log pH, GH, KH, NO₂ and NO₃ after each water change – and see how the values develop over time.

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Automatic dosing amounts

Water conditioner, fertilizer or medication: get the right dose instantly, calculated from your net volume.

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More features

Your tank, fully under control

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Substrate calculator

How much gravel, sand or aqua soil do you need? Calculate the amount in liters and kg – including two-layer setups.

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RO/DI mixing calculator

Use your net volume directly: instantly calculate the RO/tap water mixing ratio for your next water change.

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Fish stocking calculator

How many fish can your tank support? Check stocking density based on net volume and cross-check with the species database.

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CO₂ calculator

How long does it take for the tank to reach the CO₂ target level after startup? Ramp-up time based on your net volume.

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Maintenance reminders

Filter maintenance, water changes, CO₂ refills – all reminders based on your tank profile, via push or email.

Frequently asked questions
How do you calculate the net volume of an aquarium?
Net = gross × (1 – substrate deduction %) × fill level %. Gross = length × width × height ÷ 1000 L. Example: 100 × 40 × 50 cm = 200 L gross. With a 20% deduction and 90% fill level: 200 × 0.8 × 0.9 = 144 L net.
Why does net volume differ so much from the manufacturer's stated volume?
Manufacturers state the gross volume (outer dimensions or inner dimensions × full height). In real operation, substrate, decor and the safety gap at the top reduce that. For a well-set-up tank, 75–85% of the gross volume is realistic.
Which volume do I use for dosing amounts?
Always the net volume. Whether it's fertilizer, water conditioner or medication – all dosing instructions refer to the actual water volume, not the tank's outer dimensions.
How often should I do a water change?
As a rule of thumb: 25–30% per week for a normal tank. More heavily stocked tanks or tanks without plants: 30–50%. During cycling, daily partial changes may be needed depending on NH₃/NO₂ levels.
Do I need net volume to choose a filter?
For filter sizing, use gross volume as the baseline – filters should cover the total volume. For filter biology and nitrate breakdown, however, net volume (the actual water mass) is what matters.
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Set up & track your tank

Add your tank, save its volume, and track water changes and water parameters – free, no download.

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