Aquarium Volume Calculator
Cubic inches
2400
Gallons
10.4
How it works
Accurate aquarium volume calculation is essential for: correct fish stocking density (volume per fish rules), medication dosing (underdosing is ineffective; overdosing harms fish), chemical treatment quantities (dechlorinator, fertiliser, salt), and heater/filter sizing. The Aquarium Volume Calculator handles rectangular tanks, cylinder tanks, bowfront and corner tanks, and adjusts for substrate and decorations.
**Rectangular tank** Volume (litres) = length (cm) × width (cm) × height (cm) / 1000. For a standard 60cm × 30cm × 36cm tank: V = 60 × 30 × 36 / 1000 = 64.8 litres.
**Common tank sizes (typical volume)** Nano tank (30cm cube): ~27 litres. Standard 60cm: ~60–70 litres. 4-foot (120cm × 45cm × 45cm): ~243 litres. 6-foot (180cm × 60cm × 60cm): ~648 litres.
**Net water volume adjustments** Actual water volume is less than tank volume due to: substrate (gravel/sand: typically 5cm deep in a 60cm tank = 60×30×5/1000 = 9 litres displaced). Rocks and decorations: estimate displacement by volume. Filter equipment in sump: sump volume counts toward total system volume for fish stocking calculations.
**Stocking rules** Traditional "inch per gallon" rule: maximum 1 inch of adult fish body length per gallon (3.78 litres). More modern guidance accounts for fish body mass, activity level, and filtration quality. Heavily planted tanks with good filtration can support higher stocking densities.
**Medication dosing** Most fish medications are dosed per litre or per gallon. Using total tank volume (not net water volume) typically over-doses slightly — safe for most medications but potentially harmful for some copper-based treatments. The calculator outputs both total volume and estimated net water volume.
Privacy: all calculations run in the browser. No data is transmitted.
Frequently Asked Questions
- 20 US gallons = 75.7 litres. Traditional 'inch per gallon' rule: 20 inches of adult fish body length maximum. That's approximately 4–5 small tropical fish (neon tetras ≈ 1.5in adult size = 13 fish; guppies ≈ 2in = 10 fish; a betta alone = 2.5in = just one per tank due to aggression). Modern guidance updates the rule: small, active schooling fish: 1cm per litre for fish up to 5cm body length. Medium community fish: 2–3 litres per fish. Large fish or messy fish (cichlids, goldfish): 10–15 litres per fish minimum. Always err on the side of fewer fish — overstocking leads to poor water quality, disease, and stress.
- Yes — surface area (not volume) determines oxygen exchange and bio-loading capacity. Tall narrow tanks (high aspect ratio: height > width) have less surface area per litre than shallow wide tanks. A 100-litre tall column tank (30cm × 30cm × 110cm) has 900 cm² surface area; a 100-litre standard tank (80cm × 35cm × 36cm) has 2800 cm² surface area. The wider tank supports significantly more fish because more surface area = more gas exchange + more gallons of established filtration media. Bowfront tanks and hexagonal tanks are aesthetically appealing but have less efficient surface-to-volume ratios than rectangulars.
- Dechlorinator (sodium thiosulphate based) is typically dosed at 1ml per 40–50 litres to neutralise chlorine and chloramine in tap water. For a 100-litre water change: 2–2.5ml of standard dechlorinator. Use actual tank volume, not net water volume — it's safe to slightly over-dose dechlorinator. Important: chloramine (used by many water utilities) requires a dechlorinator that specifically states it treats chloramine — not all do. Check your water supplier's annual water quality report or phone them to confirm whether your water is chlorinated or chloraminated.
- For a properly cycled, moderately stocked community tank: 25–30% weekly water change is the maintenance standard. More frequent changes: lightly stocked planted tanks can go 2 weeks. Heavily stocked or messy fish (cichlids, goldfish): 2–3 times per week may be needed to keep nitrates below 20ppm. Never change more than 50% at once — the osmotic shock and temperature change stress fish. Planted tanks with CO2 injection: nitrate uptake by plants reduces change frequency but phosphate and micronutrient depletion still require regular partial changes. Always use dechlorinated water at the same temperature (±2°C) as the tank.