Aquarium planning, volume and equipment

Aquarium Volume Calculator

Calculate gross and estimated usable aquarium volume for six tank shapes. Account for glass, waterline, substrate, décor and a sump, then plan water changes, filtration, heating and label-based dosing.

Plan the water that actually fits inside the tank, not only the outside box.

Build your aquarium profile

Choose a tank shape and enter its dimensions. Advanced adjustments refine the usable-water estimate.

Aquarium type

Tank shape

Measured dimensionsLength unit

Inside dimensions are more accurate. When outside dimensions are selected, glass thickness is deducted automatically.

Inside lengthInside widthTank height

Usable-water adjustments

Optional values estimate the water displaced by the tank structure, air gap, substrate and décor.

Glass thicknessGap below the topAverage substrate depthDécor and equipment displacement (%)Operating sump volumeSump volume unit

Temperature and equipment estimate

These planning ranges are starting points. Always check the requirements of your livestock and the equipment manufacturer.

Room temperatureTarget water temperatureTemperature unit

Optional product-dose helper

Enter the ratio printed on a conditioner, fertiliser or treatment label. The calculator scales that label ratio to the estimated usable water volume.

Label dose amount (mL)For this water volume (L)

Estimated usable water volume

Your aquarium volume plan

–L

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Gross internal volume–

Estimated water weight–

Space removed by adjustments–

Live tank profile

The water and substrate levels update with your entries. The diagram is illustrative and not an engineering drawing.

Gross volume retained–

Calculation breakdown

Shape formula: –
Volume after glass adjustment: –
After waterline and substrate: –
After décor displacement: –
Operating sump contribution: –
Water density used: –

Water-change amounts

Use the estimated usable volume when preparing replacement water.

10% water change–

20% water change–

25% water change–

30% water change–

50% water change–

Planning estimates

Starting filter-flow range–Estimated hourly turnover based on the selected aquarium type.

Estimated heater capacity–A rough range based on usable litres and the temperature rise. Room conditions, tank covers and manufacturer guidance can change the requirement.

Product amount from your label ratio–Enter a product-label ratio to calculate an amount.

This calculator provides planning estimates, not structural, electrical, veterinary or chemical-treatment advice. Confirm load-bearing capacity, equipment sizes and all treatment doses with the relevant qualified professional or manufacturer.

Measure the inside of the tank

Measure clear internal dimensions wherever possible. Outside dimensions can overstate capacity because glass, frames and seams occupy space.

Plan water changes from usable volume

A nominal 200-litre tank rarely contains 200 litres of water after the air gap, substrate, rocks, wood and equipment are included.

Size equipment for the real water volume

Filter and heater labels often use aquarium capacity. Start with usable litres, then account for livestock, room temperature and manufacturer instructions.

Canister filter, aquarium heater, thermometer and circulation pump beside a planted aquarium — Use the result as a starting point, then verify each product’s specifications.

Freshwater, planted and marine tanks

Different aquarium styles may need different circulation and equipment choices. The calculator keeps volume geometry separate from husbandry decisions.

Realistic planted freshwater community aquarium — Freshwater and planted aquariums often lose substantial water space to substrate and hardscape.

Realistic marine reef aquarium with corals and reef fish — Marine systems may include a sump; enter only its normal operating water volume.

Tank shapes and assumptions

Rectangular, cube, cylinder, quarter-circle and regular-hexagon volumes use standard geometry. Bow-front and corner tanks vary by manufacturer, so their results are estimates.

Accuracy checklist

Measure the inside glass surfaces instead of the cabinet or outside frame.
Use the real fill line, not the full glass height.
Estimate average substrate depth, including slopes.
Use a conservative displacement percentage for rocks, wood and internal equipment.
For a sump, enter the normal operating volume rather than its empty capacity.
Do not use a simple volume rule alone to decide how many fish to keep.

Realistic cylindrical planted aquarium in a home interior — For a cylinder, measure the inside diameter through the centre and the usable height.

Aquarium Volume Calculator FAQ

Should I measure the inside or outside of my aquarium?

Inside measurements usually give the best volume estimate. If only outside measurements are available, select outside dimensions and enter the glass thickness so the calculator can make an adjustment.

Why is usable volume lower than the advertised tank size?

Manufacturers often quote nominal or outside volume. The air gap, glass, substrate, rocks, wood, equipment and incomplete sump fill all reduce the water actually present.

Does aquarium water weigh one kilogram per litre?

Fresh water is close to one kilogram per litre, while saltwater is slightly denser. The displayed water weight excludes the tank, stand, substrate, décor and equipment.

How much water should I prepare for a water change?

The page shows common percentages based on estimated usable volume. Match the amount and frequency to your aquarium, livestock and water-quality plan.

Is the filter-flow estimate a strict requirement?

No. It is a starting range based on hourly turnover. Media, head height, plumbing, livestock and aquarium style can change the appropriate filter and circulation flow.

Can I use the dose helper for medicine?

Only use the exact ratio printed on the relevant product label or supplied by a qualified professional. The helper scales that ratio; it does not recommend a treatment or dose.

How accurate is the bow-front calculation?

It models the front bulge as half of an ellipse added to a rear rectangle. Real bow-front shapes differ, so a manufacturer’s internal-capacity figure or direct filling measurement is more accurate.

Can I use aquarium volume to calculate stocking?

Volume is only one factor. Adult fish size, behaviour, swimming space, filtration, oxygenation and water quality must also be considered for each species.