Aquarium Calculators
GallonMath is a free set of aquarium calculators for home fishkeepers. Work out your fish tank volume in US gallons or litres, check how heavily it is stocked, size the substrate bed and the heater, and convert a specific-gravity reading into salinity for a saltwater tank. Every tool is simple, honest math, cited to primary sources — NIST and USGS for the physics, and university-extension and oceanographic standards for the husbandry — and every guideline comes with its limits spelled out.
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Aquarium Volume Calculator
Find your fish tank volume in US gallons and litres from its shape and dimensions — rectangular, bowfront, cylinder, hexagonal or corner — plus filled weight.
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Aquarium Stocking Calculator
Estimate how heavily your aquarium is stocked from its volume, filter turnover and total adult fish length — a guideline understocked, ok or overstocked read.
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Aquarium Substrate Calculator
Work out how much aquarium gravel, sand, planted aggregate or crushed coral to buy from the footprint and bed depth — weight in pounds, kilograms and bags.
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Aquarium Heater Size Calculator
Size an aquarium heater in watts from your tank volume, room temperature and target temperature — physics-based (Q = m·c·ΔT), cross-checked to watts per gallon.
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Aquarium Salinity Calculator
Convert specific gravity to salinity in ppt with a temperature correction, check it against reef, FOWLR, brackish or hyposalinity targets, and dose the fix.