Aquarium Volume Calculator — Water Level, Substrate & Sump

Measure tank water in six shapes, account for substrate and decor, add operating sump water, and compare your estimate with a measured fill.

Measure the inside of your tank. Separate its full capacity from the water it holds at your chosen level. Enter decimals such as 5.5 or 5,5, without thousands separators.

Estimated operating water · display + sump

50.4 L

13.3143 US gal · 11.0865 Imperial gal

Inside 60 × 30 × 30 cm; water depth 28 cm. No displacement or sump added.

Calculated example. Loading interactive controls…

Your tank

ShapeVertical walls and a flat bottom.

Dimension unitChanging units preserves your measurements.

Inside length / front chordStraight distance across the front, in cm.

Inside front-to-back depthFor a bow front, measure only to the straight chord line.

Inside height to the rimBottom to the top edge.

Water depth from the bottomInclude the submerged substrate layer. Do not measure from its top.

Plan view · measurement guide

Water and solids · schematic section

Internal dimensions. The section is schematic, not a tank or stand design.

Account for substrate, decor or a sump

Gravel contains water between its particles. Enter a known solid displacement, or estimate solids from a submerged uniform bed. Choose one method for the same material.

Substrate accountingNo automatic deduction for a “typical” aquarium.

Volume unitApplies to entered volumes and the main answer.

Other submerged solid displacementRock, wood or equipment; do not count the same material twice.

Additional operating waterSump/filter/pipe water at operating level, not their rim capacity.

Check against water actually added

Use a measured fill for this exact level and configuration. Record only the water present now; exclude discarded water and avoid counting existing water twice.

Measured fill volumeIn the selected volume unit. This measurement stays in this browser tab.

What did you measure?Display-only measurements compare the tank, not the whole system.

No measured fill recorded. The answer uses the geometric estimate.

Plan a water quantity

Choose your own percentage of the whole-system volume. This gives a quantity to prepare; it does not prescribe a safe change rate or predict a level drop.

Planning percentage (%)0–100%, using a current whole-system measurement when recorded.

Prepare 12.6 L for 25% of estimated whole-system water.

Where the volume goes

Capacity to the rim: 54 L
Space below the rim: 3.6 L
Filled space before solids: 50.4 L
Solid displacement: 0 L
Estimated display water: 50.4 L
Additional operating water: 0 L

No substrate deduction is included.

Estimate and measurement are different

A geometric estimate uses your inside dimensions and a flat-bottom, vertical-wall model. A bow front uses an ideal circular segment; a real manufacturer’s curve may differ. A regular hexagon needs six equal sides. Display water = filled space − submerged solid displacement. Whole-system water adds separately entered operating sump, filter and pipe water.

For a submerged uniform bed, solid displacement = footprint × bed depth × (1 − pore fraction). Water in pores remains part of the contained volume, but it is not evidence that all water mixes instantly or can be removed in a water change. A measured fill is usually more informative than choosing a generic displacement percentage. Recheck it after changing the level, substrate, decor or equipment.

Illustrative presets use declared assumptions, not branded tank specifications. “Gravel + sump” uses a user-editable 40% pore fraction solely as an example. This tool does not determine fish stocking, medicine or salt doses, glass construction, or floor/stand capacity.

Inputs behind the four editable examples

All examples use centimetres and litres, 25% planning quantity, no recorded measurement, and a flat bottom. Choose an example above to load its complete inputs.

60 cm bare tank: rectangular 60 × 30 × 30 cm; water depth 28 cm; substrate, decor and sump displacement/addition 0 L. Estimated system water 50.4 L; 25% = 12.6 L.
Gravel + sump: same rectangle and level; uniform 5 cm bed with illustrative 40% water-filled pores, 3 L other solids, 12 L operating sump. Bed 9 L = 5.4 L solids + 3.6 L pores; display water 42 L, system 54 L; 25% = 13.5 L.
Bow-front tank: front chord 80 cm; straight body depth 30 cm; circular bow depth 10 cm; height 45 cm; water depth 42 cm; known substrate solids 5 L, other solids 2 L, sump 0 L.
Round tank: full inside diameter 40 cm; height 50 cm; water depth 45 cm; no substrate deduction, other solids 2 L, sump 0 L. Estimated water 54.5487 L; 25% = 13.6372 L.

Sources: LSU tank-volume geometry; Wolfram circular segment; USGS porosity definition; NIST volume units.