Plant care calculator

Paludarium Water Volume & Land-to-Water Ratio Calculator

Calculate net paludarium water volume, land and water surface areas, false bottom void capacity, and minimum pump flow in metric or imperial units.

Quick Answer

The calculator estimates paludarium land and water volumes from the enclosure dimensions, land-to-water ratio, substrate depth, and selected false-bottom setup. For an eggcrate false bottom, it models the hidden void at about 95% usable water-filled space, while other drainage-layer setups use their specified assumptions. The result helps estimate how much land and water volume your paludarium provides before accounting for irregular hardscape, plants, or other displacement.

Updated Reviewed Reading time: 6 min

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Scenario Presets

cm
cm

Internal length of the enclosure. Imperial entries are converted with 2.54 cm per inch.

cm
cm

Internal depth from front glass to back glass.

cm
cm

Internal height from the base to the top rim, used for gross volume and the headroom check.

cm

Depth of standing water. Also used as the height of the void under the land.

%

Percentage of the total floor footprint allocated to the terrestrial land section.

Eggcrate voids provide open water reservoirs under the land; LECA holds water only in inter-particle pore spaces.

%

Estimated percentage of submerged volume occupied by rocks, driftwood, and foam backgrounds.

Determines minimum delivered pump flow required at operating head height.

Recommended Output

Architectural Cross-Section
Air Headroom: --
CANOPY AIR HEADROOM TERRESTRIAL BANK (50%) AQUATIC COLUMN NET WATER DRAINAGE VOID (95%)
Net Water Capacity -- %
--

Actual water available for filtration, dosing, and aquatic life after subtracting land footprint, substrate void, and hardscape displacement.

Min Pump Flow Target
--

Required delivered turnover flow for water features and filtration.

Terrestrial Zone

Land Footprint Area

--

False Bottom Void Volume

--
Aquatic Zone

Water Surface Area

--

Open Water Basin Volume

--
Gross Enclosure Size
--

Total internal glass volume (L × W × H).

The Problem

A paludarium's glass volume says very little about its real water volume, because land, hardscape and the false bottom void all change it. Keepers need a net water figure to size pumps, dose treatments, plan water changes and choose livestock.

When to Use This Tool

When planning a new paludarium and deciding how much of the footprint should be land versus water.,When sizing a pump or filter from the true water volume instead of the glass volume.,When estimating how much water an eggcrate or LECA false bottom void adds to the system.,When working out how much water to prepare for a first fill or a large water change.,When comparing eggcrate, LECA and solid-bank builds for the same tank.

Who is this for?

  • Paludarium and riparium builders
  • Keepers planning vampire crab or other semi-aquatic setups
  • Aquascapers adding waterfalls, streams and hidden pump chambers

Why Glass Volume Misleads in a Paludarium

Paludarium false bottom land terrace and water barrier
Land Terrace & Water Barrier Division: Constructing a false bottom barrier to separate land substrate from the submerged aquatic water reservoir.

A paludarium's glass volume overstates its water. Part of the footprint is land, part of the height is air, and rock, wood and foam take up room. This calculator turns your dimensions into a net water figure you can use for pump sizing, dosing and water changes. If you are still deciding how much of the tank should be land, the riparium vs paludarium comparison explains how the land-to-water split changes what the build can support.

How to Use the Calculator

  1. Enter the internal tank dimensions: length, width (front to back) and height, measured inside the glass.
  2. Set the water depth: the depth of standing water. With a false bottom, this is also the height of the water-filled void under the land.
  3. Choose the land footprint: the share of the floor that is land, from 10% to 90%.
  4. Pick the false bottom type: an eggcrate void holds the most hidden water, LECA or gravel holds less, and a solid bank holds none.
  5. Estimate hardscape displacement: rock-heavy and foam-heavy builds hold less water than sparse ones.
  6. Select the turnover rate: 5x for circulation only, 8x for a stream or waterfall, 10x for a heavy waterfall.

What Each Result Means

  • Total tank volume: gross glass volume, useful for stand weight and glass planning, not for dosing.
  • Water zone and land zone area: the footprint split in cm² and sq in.
  • Open water volume: the exposed pool before displacement.
  • False bottom void volume: hidden water under the land before displacement.
  • Net water volume: the figure to use for dosing and water changes.
  • Minimum delivered pump flow: the flow you need at the outlet after head loss. The paludarium water circulation pumps guide explains how to convert it into a nominal pump rating that accounts for vertical lift.

Choosing a False Bottom Type

An eggcrate void gives the most hidden water and the easiest maintenance access. A LECA or gravel layer is simpler to build and holds less water because it only fills the gaps between particles. A solid bank holds no water under the land, so all water sits in the open pool. Construction details for each approach are in the paludarium land-to-water barrier guide.

Sizing Water Volume for Plants and Animals

Semi-aquatic animals such as the species in our vampire crab paludarium guide care more about land area, humidity and easy exits than about a large water volume. Fish need real net volume and filtration. Shoreline plants such as Bucephalandra and Anubias nana grow on rock at the water margin and are not limited by net volume, but they need that margin to exist, so keep some shallow water and exposed rock in your layout.

Presets and Worked Examples

The three presets show how land share, void type and displacement change the result across tank sizes. Each worked example lists every step, so you can audit the numbers by hand.

Preset names are labels for the tank footprint class. The actual net water volumes are much smaller than the nominal gallon figures, which is normal for a land-heavy build.

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Troubleshooting & Diagnostics Guide

1 Net water volume is far lower than the tank's gross volume

Diagnosis: Gross volume includes land, the air above the waterline and hardscape. In land-heavy builds the net figure is often 15% to 30% of gross.

Treatment: This is expected. Use net volume for pump sizing, dosing and water changes, and use gross volume only for glass and stand planning.

2 A warning says there is too little height above the waterline

Diagnosis: Tank height minus water depth is under 10 cm (4 in), leaving little room for land, plants and an air gap above the water table.

Treatment: Lower the water depth or choose a taller tank. A land surface that sits too close to the water invites capillary wicking.

3 Calculated pump flow seems too small for the waterfall

Diagnosis: The result is a delivered-flow target at the outlet, and a pump's nominal rating drops sharply with vertical lift.

Treatment: Measure the vertical distance from the waterline to the outlet and check the pump's flow curve at that head. See the circulation pumps guide for a sizing procedure.

4 Real water volume is lower than the calculator result

Diagnosis: More hardscape than estimated, an eggcrate void partly blocked by substrate or mesh, or a waterline below the assumed depth.

Treatment: Raise the hardscape displacement percentage, confirm the void is open, and re-measure the water depth.

Glossary of Terms

False Bottom
A supported panel, often eggcrate, that holds the land substrate above a water-filled void so soil does not touch standing water.
Capillary Break
An air gap or non-porous barrier that stops soil from wicking water upward from the water table.
Net Water Volume
The volume of standing water in the system after accounting for land, the false bottom void and hardscape displacement.
Turnover Rate
The number of times per hour a pump moves the full water volume.
LECA
Lightweight expanded clay aggregate, a porous drainage material with open space between particles.

Frequently Asked Questions

How do I calculate water volume for a bowfront or curved tank?
The calculator assumes a rectangular box. For a bowfront, approximate the bulge as a parabolic segment: add two thirds of the bow depth to the front-to-back width and enter that effective width. For a cylinder, enter a length and width that give the same footprint (pi times radius squared). Treat the result as an estimate, because curved glass and trim also change the real figure.
How much water volume do vampire crabs need compared with fish?
Vampire crabs and similar semi-aquatic animals depend more on land area, humidity and easy exits than on water volume, so a land-heavy build with a modest pool can suit them. Fish need real net water volume, filtration and depth, so size them from the net water figure and plan a larger water zone. Check each species' care requirements, and see the vampire crab paludarium guide for layout needs.
Does saturated substrate count as water volume?
No. The calculator counts standing water only. Wet substrate holds water in its pores, but that water is not available for pumping or water changes and should not count toward pump sizing. It does mean your first fill drops faster than the arithmetic suggests, because the substrate absorbs water while it saturates.
How do I plan for evaporation and evapotranspiration refills?
Land plants, waterfalls, splash and heating all increase water loss. The simplest method is to measure it: mark the waterline, let the tank run for a week and record how far the level drops. Liters lost equals water zone area in cm² times the drop in cm, divided by 1000. Use that figure to size an auto top-off or reservoir, and top up with dechlorinated or RO water to avoid mineral buildup.
How does pump head height affect the recommended flow?
The recommended flow is the flow you need delivered at the outlet. A pump's flow falls as vertical lift rises, and a pump rated at 100 GPH can deliver only 30 to 40 GPH at 60 cm (24 in) of head. Choose a pump whose flow curve meets the target at your real head height and add a margin for friction in tubing and valves. The paludarium water circulation pumps guide walks through this.
Why does the false bottom void count as water?
Water fills the open space under the land up to the waterline, so an eggcrate void is a real reservoir that mixes with the pool. It dilutes waste and stabilizes temperature and chemistry. LECA or gravel only holds water in the gaps between particles, which is why it uses a lower void fraction of 0.40.
How should I estimate hardscape displacement?
Sparse builds with a few rocks and a branch are often around 10% to 15%. Dense rockwork, thick foam backgrounds and large driftwood can reach 25% to 40%. These are rules of thumb. For better accuracy, fill a bucket to a mark, add the hardscape and measure the rise.
Why is displacement applied to the void as well as the pool?
It is a simplification that keeps the model easy to use. Most hardscape sits in the pool or on the land, so applying displacement to the whole total can understate water slightly when the void is kept clear. Reduce the percentage if your void is largely empty.
Which turnover rate should I choose?
Use 5x for a still pool with basic circulation, 8x when the pump feeds a stream or waterfall, and 10x for a heavy waterfall or a deliberately higher-circulation target. A higher rate adds noise, splash and evaporation, so choose the lowest rate that keeps the water moving.
Is the land footprint percentage the same as land volume?
No. It is a share of the floor area. Land volume depends on how high you build the land above the water, which the calculator does not track. It uses the footprint only to split water and land areas.