# Aquarium sump volume calculator

> Add your display tank, sump chamber, and refugium to get the total system water volume in US gallons and liters. A 48 × 18 × 21 in (≈ 122 × 46 × 53 cm) display with a 36 × 12 × 12 in (≈ 91 × 30 × 30 cm) sump and an 18 × 12 × 8 in (≈ 46 × 30 × 20 cm) refugium holds 108.5 US gal (≈ 411 L) of system water — the worked example below uses the same inputs, so the numbers shown here always match the calculator.

Use the interactive calculator on the page: https://petguidecalc.com/aquarium/sump-volume-calculator/. Add the display tank, sump, and refugium dimensions to get the total system water volume.

> **Research note**: Optimal sump sizing has no peer-reviewed study (research gap as of 2026); the table is a hobby convention. System volume math is standard geometry.

## What is the total water volume of my system?

The total system volume is the display tank plus the sump chamber plus the refugium, summed as US gallons with the liter total alongside. Measure the sump at its operating water level, not the glass height, because only the water actually in each chamber counts.

## Common sump sizes by display tank

| Display tank | Minimum sump | Recommended | Note |
|---|---|---|---|
| 30–55 gal | 10 gal | 15–20 gal | Standard 20 gal long fits most stands |
| 56–75 gal | 15 gal | 20–29 gal | 29 gal common |
| 76–120 gal | 20 gal | 30–40 gal | Dedicated sump |
| 121–180 gal | 30 gal | 40–55 gal | Common two-chamber |
| 180+ gal | 40 gal | 55–75 gal | Custom |

Hobby convention, not a peer-reviewed standard. Verify the sump fits the stand and cannot overflow when the return pump is off.

## How the system volume is calculated

Each component uses the same geometry as the shape volume calculators — a 48 × 18 × 21 in display is a rectangular box of 78.5 US gal (297 L), and the 36 × 12 × 12 in sump chamber adds 22.4 US gal (85 L) of water at its run level.

The sump and refugium heights are the run-level water height: measure the operating water level, because the water line sits below the glass rim in most sump compartments.

Worked example from the calculator: 78.5 US gal (display) + 22.4 US gal (sump) + 7.5 US gal (refugium) = 108.5 US gal (410.6 L) of total system water. Change any component and the total updates from the same shared formula.

## Sump sizing questions

**Q: What should the sump water height be set to?**

Set it to the run-level water height — the operating water level you measure while the system runs, not the glass height of the sump. Only the water actually in the chamber counts toward the system volume.

**Q: How big should my sump be for my display tank?**

The sizing table on this page is a hobby convention, not a peer-reviewed standard: roughly 15–20% of display volume for most tanks, with bigger custom builds going higher. There is no published optimal-sump study as of 2026.

**Q: Does a bigger sump always help?**

A larger sump adds water volume, which dilutes waste and gives the biofilter more room, but it must fit the stand and must never overflow when the return pump shuts off. Balance size against cabinet space and the sump volume you can actually service.

**Q: What is a refugium for?**

A refugium is a separate chamber for macroalgae, live rock, or copepods that adds both water volume and biological filtration capacity. It counts as part of the total system water.

**Q: How does sump volume relate to the nitrogen cycle?**

More water volume means a larger reservoir for ammonia, nitrite, and nitrate, and a bigger sump gives the biological filter more surface area. Aquarium-scale biofilter research (Pungrasmi et al. 2013) is the background for why sump volume matters to filtration.

## References

The geometry is standard; the density anchors back the liter-to-gallon and weight conversions, and Pungrasmi provides the aquarium-scale biofiltration context for why sump volume matters.

- [Guide for the Use of the International System of Units (SI) — Special Publication 811 (2008 Edition)](https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication811e2008.pdf) — Thompson A, Taylor BN, NIST Special Publication 811, 2008. Defines the liter–cubic-meter relationship and the US gallon ≈ 3.785412 L used for volume conversion on this page.
- [NIST Handbook 44 — Appendix C: General Tables of Units of Measurement (2024 Edition)](https://www.nist.gov/document/nist-hb-44-2024-appendix-c-general-tables-units-measurement) — National Institute of Standards and Technology, NIST Handbook 44, 2024. Confirms 1 US gallon = 231 cubic inches exactly (statutory definition) — the conversion anchor for the cubic-inch result.
- [ITS-90 Density of Water Formulation for Volumetric Standards Calibration](https://pmc.ncbi.nlm.nih.gov/articles/PMC4909168/) — Jones FE, Harris GL, Journal of Research of the National Institute of Standards and Technology, 1992. Freshwater density ρ = 0.99820 g/cm³ at 16.67 °C (62 °F) via the ITS-90 formulation — basis of the ≈8.34 lb/US gal freshwater weight shown here.
- [International one-atmosphere equation of state of seawater](https://www.sciencedirect.com/science/article/pii/0198014981901229) — Millero FJ, Poisson A, Deep-Sea Research Part A. Oceanographic Research Papers, 1981. Standard seawater density at 25 °C, S = 35: ρ ≈ 1.024 g/cm³, specific gravity ≈ 1.025 relative to pure water at 25 °C; adopted by UNESCO/IOC/ICES/SCOR/IAPSO and superseded by TEOS-10 (2010). Basis of the saltwater weight shown here.
- [Optimization and evaluation of a bottom substrate denitrification tank for nitrate removal from a recirculating aquaculture system](https://doi.org/10.1016/s1001-0742(12)60248-4) — Pungrasmi W, Playchoom C, Powtongsook S, J Environ Sci (China), 2013. Aquarium-scale experimental biofilter in an 8 L recirculating system — background for why sump volume matters to biological filtration and the nitrogen cycle.

_Educational resource, not veterinary advice. PetGuideCalc — https://petguidecalc.com_