Tool
Aquarium Sump Volume Calculator
Reef dosing, salt mixing and skimmer sizing all depend on the whole system, not the display alone. Add the display tank, sump and refugium together to get total system volume.
Required
Display tank
Display tank:
Optional
Sump
Measure water height to the operating water line, not the sump wall.
Sump:
Optional
Refugium
Include only the water-filled section of the refugium.
Refugium:
Common sump sizing guidelines
| Display tank | Minimum sump | Recommended sump | Notes |
|---|---|---|---|
| 30–55 gal | 10 gal | 15–20 gal | A standard 20 long fits under most stands |
| 56–75 gal | 15 gal | 20–29 gal | A 29 gallon tank is a common choice |
| 76–120 gal | 20 gal | 30–40 gal | Purpose-built sump recommended |
| 121–180 gal | 30 gal | 40–55 gal | Dual-chamber sump common |
| 180+ gal | 40 gal | 55–75 gal | Custom build typical |
Why total system volume matters
Everything dissolved in a reef system is shared across the display, the sump and any refugium. Alkalinity, calcium and magnesium dosing calculators ask for system volume because a dose spread over 100 gallons produces a different concentration than the same dose in 75. Skimmer and return pump ratings are likewise quoted against the whole system. Underestimating by a 25-gallon sump means every dose is a third too strong.
Measure the sump to its operating water line, not the top of the glass; the space above the water line is there to absorb back-siphon when the return pump stops. For refugiums, include only the flooded chamber.