Fish & Aquarium
Calculators
From fish weight formulas for anglers to aquarium stocking and tank volume tools — every calculator is free, instant, and vet-informed. No sign-ups needed.
Fish Calculators
20+ free tools for anglers, fish owners, and aquarium enthusiasts.
Fish Weight Calculator
Estimate fish weight from length and girth using species-specific formulas. Works for 30+ species.
Calculate →Fish Length to Weight Calculator
Convert fish length to estimated weight using empirical formulas for bass, trout, salmon and more.
Calculate →Bass Weight Calculator
Estimate largemouth or smallmouth bass weight from length and girth. Uses the standard 1200 divisor formula.
Calculate →Trout Weight Calculator
Calculate rainbow, brown, or lake trout weight using the 800 divisor formula (Length × Girth² ÷ 800).
Calculate →Catfish Weight Calculator
Estimate blue, channel, or flathead catfish weight using body shape-adjusted weight formulas.
Calculate →Salmon Weight Calculator
Estimate Atlantic, Chinook, or Coho salmon weight from length and girth measurements.
Calculate →Walleye Weight Calculator
Calculate walleye weight from length using the standard formula (Length³ ÷ 2700) used by anglers.
Calculate →Pike Weight Calculator
Estimate northern pike or muskellunge weight from length measurements using species-specific formulas.
Calculate →Saltwater Fish Weight Calculator
Weight estimates for redfish, snook, striped bass, flounder, and other common saltwater species.
Calculate →Aquarium Stocking Calculator
Calculate how many fish your tank can hold based on adult size, bioload, and species compatibility.
Calculate →Fish Tank Volume Calculator
Convert your tank’s dimensions (length × width × height) into total water capacity in gallons or liters.
Calculate →Fish Tank Size Calculator
Find the minimum tank size for your chosen fish species based on adult length and schooling requirements.
Calculate →Fish Tank Gallon Calculator
Calculate exact gallons for rectangular, bow-front, hexagonal, and cylindrical aquarium shapes.
Calculate →Koi Pond Stocking Calculator
Determine safe koi stocking levels for your pond volume, using the 10-gallon-per-inch guideline and filtration.
Calculate →Betta Tank Size Calculator
Calculate the ideal tank size and setup for betta fish based on sex, tank mates, and enrichment needs.
Calculate →Goldfish Tank Calculator
Goldfish need far more space than the “inch per gallon” myth suggests. Get the right tank size for your variety.
Calculate →Stocking Density Calculator
Calculate the stocking density of your community tank in inches-per-gallon and compare to recommended maximums.
Calculate →Fish Feeding Calculator
How much should you feed your fish? Calculate daily portion sizes by species, weight, and food type.
Calculate →Fish Food Portion Calculator
Prevent overfeeding and poor water quality — calculate the right flake, pellet, or live food portions per fish.
Calculate →Fish Consumption Calculator
Calculate safe weekly fish consumption based on species, mercury levels, and body weight for adults and children.
Calculate →Aquarium Water Change Calculator
Calculate the volume of water to change and how often to maintain safe ammonia, nitrite, and nitrate levels.
Calculate →Fish Tank Heater Size Calculator
Find the right wattage heater for your aquarium based on tank volume and target vs. ambient temperature difference.
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Frequently Asked Questions
Common questions about our fish calculators and how to use them.
The most common formula is: Weight = (Length × Girth²) ÷ Factor. The divisor varies by species shape — 800 for cylindrical fish like trout, 900 for salmon, 1,200 for bass using length and girth, and 2,700 for the long, slender walleye using only length cubed. Enter your measurements in inches to get weight in pounds.
The old “one inch of fish per gallon” rule is outdated. Modern fishkeeping recommends considering the fish’s adult size, waste output (bioload), swimming style, and filtration capacity. A good starting point is 1 inch of adult fish per 2 gallons for most community fish, but bottom-dwellers, schooling species, and active swimmers need more space. Our Aquarium Stocking Calculator applies these modern guidelines automatically.
Fish weight calculators give a close estimate — typically within 5–15% of actual weight for average-condition fish. Accuracy improves when you enter the girth measurement (taken just in front of the dorsal fin), as body shape varies significantly between individuals, seasons, and spawning condition. For competition weigh-ins, always use a certified scale.
Absolutely! Visit our contact page and describe the tool you need. Popular requests — like a carp weight calculator or pond liner size calculator — go straight to the top of our build queue.