Aquarium calculators that show their math
Free, fast tools for fishkeepers: tank volume for any shape, water changes, substrate, heater sizing, unit conversion and dose scaling. Every result shows the formula, and the constants come from NIST and USGS.
Calculators
Tank volume by shapeGallons and liters for rectangle, bow-front, cylinder, corner and hexagon tanks.Gallons ↔ liters & water weightConvert units and see how much the water weighs.Water change & nitrate dilutionVolume to change and how fast nitrate drops over several changes.Substrate / gravel amountGravel, sand or soil for flat or sloped beds, and bags needed.Heater size & warm-up timeWattage from two published guidelines, plus warm-up time.Product dose scalingScale a label dose like “5 mL per 10 gal” to your volume.
Why another aquarium calculator?
Many answers online are a forum post with no working shown. Here you can see exactly how each number is produced, check it by hand, and adapt it to your setup. Where advice differs (heater sizing, for example) we show the competing published guidelines side by side instead of picking a single number.
All tools run in your browser and work offline once loaded.