Aquarium math, done for you.
Free calculators for freshwater and planted-tank keepers — from tank volume and heater wattage to CO2, glass thickness, and running costs. Every tool shows the formula it uses and where it comes from, so you can trust (and check) the result.
Setup & Sizing
Plan the tank itself — size, stock, and what goes in it.
Tank Volume Calculator
Litres and gallons for rectangular, cube, cylinder and bowfront tanks — with a realistic fill-level correction.
Stocking Level Estimator
A cm-per-litre starting estimate for how much fish your tank can hold — with an honest list of when the rule fails.
Substrate Calculator
Litres, kilograms and bag count for gravel, sand or aquasoil — with sloping support.
Nitrogen Cycle Timeline
A personalised week-by-week fishless cycling timeline from your start date — and what each test reading means.
Water Chemistry
Understand what your test kits are telling you.
Water Change Calculator
How many litres to change — and what % it takes to dilute nitrate from where you are to where you want to be.
Salinity Converter (SG ↔ ppt)
Convert hydrometer specific gravity to ppt salinity and back, calibrated for 25 °C readings.
CO2 Concentration Estimator
Estimate dissolved CO2 from pH and KH using the classic carbonate-equilibrium formula — limits included.
pH / KH / CO2 Chart
Interactive colour-coded chart of dissolved CO2 across pH and KH — with an honest note on when the chart lies.
Equipment & Running Costs
Pick the right gear and know what it costs to run.
Heater Wattage Calculator
Wattage from tank size and the room-to-tank temperature gap — not just a flat watts-per-gallon guess.
Filter Flow Rate Calculator
Turnover targets (4–10× per hour) with the correction most sites skip: rated flow isn't real flow.
Lighting Level Calculator
Lumen and LED-watt targets per litre for low, medium and high-light planted tanks — and why watts-per-gallon died.
Fish Food Cost Calculator
How long a container really lasts, cost per month — and whether it will expire before you finish it.
Electricity Cost Calculator
kWh and cost per month for heater, light, filter and air pump — with realistic heater duty cycles, not rated watts.
Pipe Flow Velocity Calculator
Water velocity from flow rate and pipe size — size drains and return lines that stay quiet and safe.
Structure & Safety
The physics of a heavy box of water.
Glass Thickness Reference
Hydrostatic pressure and a reference glass-thickness estimate for DIY builds — with a serious disclaimer.
Tank Weight Calculator
Filled weight in kg and lb, plus the floor-loading question every large-tank owner should ask before filling.
Why another calculator site?
Most aquarium calculators are black boxes: you type a number, you get a number, and you have no idea whether to trust it. AquaCalcs takes the opposite approach. Every page documents the formula it uses, the assumptions behind it, and — just as important — where the rule of thumb breaks down. The stocking calculator tells you why the centimetre-per-litre rule is only a starting point. The glass thickness page tells you plainly that it is a reference, not an engineering sign-off.
All tools run entirely in your browser. Nothing you type is sent to a server, and no account is required. If you spot an error or want a new tool, tell us — the site improves through reader feedback.