Calculate the volume, water weight, heater size, and filter flow rate for your fish tank or aquarium.
Total volume
64.8L
17.1 US gal
Actual water vol.
51.8L
~80% fill with substrate
Water weight
52kg
water only
Total weight (est.)
65kg
inc. substrate + glass
Heater
52W
Minimum. Use 104W in cold rooms.
Filter flow rate
260 L/h
5x turnover/hr. Use 520 L/h for heavy stocking.
Fish stocking guide
13 cm
Total adult fish length (1cm per 4L). Rough guide only.
Water change volume
13 L
25% weekly change recommendation.
Recommendations are general guidelines. Always research the specific needs of your fish species. Consult an aquatics specialist for large or specialist setups.
A full glass tank holds less water than its total volume suggests — substrate (gravel, sand) typically takes up 10–20% of the volume, decorations another 5–10%, and you should leave 2–5 cm of air gap at the top. Multiply the calculated volume by 0.75–0.85 to estimate actual water volume.
The traditional guideline is 1 inch of fish per gallon of water (roughly 4 litres). However, this is a crude approximation — a 10-inch pleco needs far more space than 10 neon tetras. Research the adult size and swimming behaviour of each species you plan to keep.
As a rule of thumb, plan 1 watt of heater power per litre of water. For tanks in cooler rooms (below 18°C), use 2 watts per litre. A 100-litre tank in an average room needs a 100W heater; in a cold garage or outhouse, use 200W.
A filter should turn over the full tank volume at least 4–6 times per hour. For a 100-litre tank, look for a filter rated at 400–600 litres per hour (l/h). For heavily stocked tanks or aggressive fish, aim for 8–10x turnover.
A new tank must be biologically 'cycled' before adding fish — this means establishing beneficial bacteria in the filter media that convert ammonia (from fish waste) into less harmful nitrate. Cycling takes 4–8 weeks with fish food or an ammonia source, or 1–2 weeks with established filter media from an existing tank.
Water weighs approximately 1 kg per litre. A 200-litre aquarium with substrate and decorations can easily weigh 250–300 kg when full. Always ensure your cabinet and floor can support this weight — furniture-grade cabinets rated for the purpose are recommended.
Calculate the volume, water weight, and equipment recommendations for your aquarium based on its dimensions and shape.
60x30x36 cm rectangle
64.8 litres total, ~49 litres water, 49 kg
120x45x45 cm rectangle
243 litres total, ~182 litres water, 182 kg
The world's largest aquarium is the Haiyang Guanlan in China, holding approximately 22 million litres of water. The largest home aquarium on record holds over 400,000 litres and is built into the wall of a private home in Germany.
Begin with the decision or task you want this page to support. Calculate the volume, water weight, heater size, and filter flow rate for your fish tank or aquarium. Write down the expected kind of answer before entering values, so you can notice if a default, unit, or mode does not fit your situation. If more than one input could change the result, hold the others steady while you test one value at a time. This makes it easier to understand what the tool is responding to instead of treating the first number on screen as a complete recommendation.
Follow the page instructions in order and check the labels as you go. The first step is: Select your tank shape: rectangular, cylindrical, or hexagonal.. Next, choose your unit of measurement (cm or inches). Use consistent units and a consistent time period, and avoid replacing an unknown value with zero unless the tool explicitly treats zero as a valid input.
The page's worked example is a reference point, not a forecast for every situation. It shows how the inputs lead to an output: 64.8 litres total, ~49 litres water, 49 kg Compare the assumptions in that example with your own values, then check the units, rounding, and any optional settings before comparing results. If your scenario differs, describe that difference explicitly rather than expecting the example's answer to transfer unchanged.
Use the result as one part of a decision rather than a substitute for the context around it. If you are comparing alternatives, run each one with the same definitions and change only the factor you want to compare. For repeated tasks, save a short note of the inputs and date; this makes later results easier to reproduce and helps distinguish a real change from a difference in how the values were entered.
A useful final check is to compare the answer with a second route: a hand calculation, a known example, an official reference, or the instructions for the service that will receive the result. One point worth checking on this page is “Why is the usable water volume lower than the tank volume?” A close match on a simple case can confirm the basic method; it does not prove that every complex case is covered.
For low-consequence tasks, a quick spot check may be enough. For anything that affects money, health, safety, access, or a deadline, verify the result against an authoritative source or the system that will use it. The tool can make routine work faster, but you remain responsible for confirming that the inputs and intended use are appropriate.
The outside dimensions describe a geometric maximum. Gravel, décor, equipment, substrate, water level, and the glass or frame reduce the water actually present. Use the result as an estimate, and measure the fill volume when dosing medication, conditioner, salt, or other products where an accurate amount protects fish.
Estimated volume provides a starting point for heater wattage, filter turnover, water changes, and treatment doses. The right choice also depends on room temperature, stocking, plant load, flow preferences, species, and the manufacturer’s instructions. Avoid treating a single litres-per-hour or watts-per-litre rule as a substitute for aquarium-specific advice.
Only after checking the actual water volume and the product label. Many treatments are dosed by litres or gallons, and overdosing can harm livestock or biological filtration. Account for water removed during a change, never mix products unless the manufacturer says it is safe, and ask an aquatic veterinarian or specialist when fish are unwell.
Record how much conditioned water you add during a refill, or calculate the filled dimensions after subtracting substrate, décor, and the unfilled space at the top. Keep the measured volume separate from the tank’s advertised capacity. Use that more conservative figure for treatments and record it where it can be checked before dosing.