Tools in This Collection
Fish Tank Volume Calculator
Calculate exact water volume for rectangular, bowfront, and hexagonal tanks
Aquarium Stocking Calculator
Estimate how many fish a tank can support based on bioload and filtration
Aquarium Fertilizer Calculator
Dose macro and micronutrients for planted tanks to EI or PPS-Pro targets
Aquarium Heater Wattage Calculator
Determine correct heater wattage at 3–5 watts per gallon for your setup
Planted Tank CO2 Calculator
Calculate CO2 injection rate to maintain 30 ppm in planted aquariums
Reef Dosing Calculator
Calculate two-part dosing for reef alkalinity, calcium, and magnesium
Brackish Water Salinity Calculator
Calculate salt amounts to achieve target specific gravity for brackish tanks
Aquarium Setup Workflow
Aquarium success depends on getting the numbers right before adding fish. Tank volume determines medication doses, stocking levels, filtration needs, and heater wattage. Running these calculations before purchase prevents the costly mistakes that come from overstocking or underpowering your system.
Tank Volume Calculation
The Fish Tank Volume Calculator determines exact water volume for rectangular, bowfront, and hexagonal tanks. Formula for rectangular tanks: length (in) × width (in) × height (in) ÷ 231 = gallons. A standard 40-gallon breeder (36" × 18" × 16") holds approximately 40 gallons — but fill only to 80–85% capacity (32–34 gallons) after substrate and decor displace water. Accurate volume is critical for medication and chemical dosing.
Stocking and Bioload
The Aquarium Stocking Calculator provides better guidance than the simplified "1 inch of fish per gallon" rule. Bioload depends on fish species temperament, adult size, activity level, and filtration capacity. A heavily planted, well-filtered 40-gallon tank can support 8–10 small tetras plus a school of corydoras — where the inch-per-gallon rule would only suggest 40 inches total. The calculator factors in filtration rating and plant density adjustments.
Planted Tank Requirements
CO2 injection is the single biggest factor in planted tank success. The Planted Tank CO2 Calculator calculates injection rate needed to maintain 30 ppm CO2 based on tank volume and target pH/KH relationship. The Aquarium Fertilizer Calculator doses macro (NPK) and micronutrients to the Estimative Index or PPS-Pro target concentrations.
Reef Tank Parameters
Reef tanks require tighter parameter control than freshwater. The Reef Dosing Calculator calculates two-part dosing quantities to maintain alkalinity (8–11 dKH), calcium (420–450 ppm), and magnesium (1250–1350 ppm) at your target levels. The Aquarium Heater Wattage Calculator determines correct heater size: 3–5 watts per gallon for most setups, with higher wattage needed for large temperature differentials in cold rooms. The Brackish Water Salinity Calculator calculates salt amounts to achieve specific gravity targets for brackish species (0.003–0.015 SG for low-end brackish; 0.018–0.025 for high-end).
Frequently Asked Questions
How many fish can I put in a 40-gallon aquarium?
The traditional 1-inch-per-gallon rule is a rough starting point — a 40-gallon tank could theoretically hold 40 inches of fish. However, bioload depends more on species than length. A 40-gallon tank can comfortably house 6–8 medium tetras, a school of 6 corydoras, and a centerpiece fish with good filtration and regular water changes. Overstocking the filter capacity causes ammonia spikes and fish stress.
How do I calculate the volume of my fish tank?
For a rectangular tank: multiply length × width × height (all in inches), then divide by 231 to get US gallons. A 48" × 12" × 18" tank = 10,368 cubic inches ÷ 231 = approximately 44.9 gallons. For non-rectangular tanks (bowfront, hexagonal), use the Fish Tank Volume Calculator which handles these shapes automatically.
What wattage aquarium heater do I need?
A general rule is 3–5 watts per gallon. For a 40-gallon tank in a room that's 65–68°F maintaining 78°F: a 150–200W heater is typically sufficient. In a cold room (below 60°F) or large temperature differential, use 5 watts per gallon. For tanks over 75 gallons, two smaller heaters placed at opposite ends provide more even temperature distribution than one large heater.
What CO2 level should I target for a planted tank?
Most planted tanks perform best at 20–30 ppm CO2. Consistent CO2 at 30 ppm significantly improves plant growth rates and helps outcompete algae. Signs of adequate CO2: plants produce visible bubble streams during peak light hours. Signs of too much CO2: fish gasping at the surface. The Planted Tank CO2 Calculator uses your tank's pH and KH readings to estimate current CO2 and calculate the injection rate needed to reach your target.