Fish Weight
Estimate the weight of any fish using its length and girth with our species-adjusted calculator. Supports bass, trout, salmon, pike and more with instant results and charts.
About This Calculator
The Fish Weight Calculator is a practical tool for anglers and fishing enthusiasts who need to estimate the weight of their catch without a scale. By entering the fish length and girth measurements, the calculator provides an instant weight estimate using species-specific formulas that account for different body shapes.
The calculation follows the standard fisheries formula: weight = length × girth² / divisor. The divisor varies by species group — 800 for bass and striper, 900 for trout and salmon, 1000 for bluegill and sunfish, 850 for carp and catfish, and 600 for sturgeon. For elongated species like gar, muskie, and pike, the calculator uses length³ / 2700 which does not require girth. If girth is not provided, it is automatically estimated as 58% of the length, a widely accepted rule of thumb among anglers.
Regional Notes: In the US and UK, anglers commonly measure fish in inches and pounds. The calculator accepts inches and meters for length, and displays results in both pounds and kilograms for international use. Fishing regulations and minimum size limits vary by region — always check local fishing authorities for specific rules in your area. In India, freshwater species like Rohu and Catla can also be estimated using the carp formula (divisor 850) as a close approximation.
This tool is ideal for catch-and-release fishing where you want to estimate weight without harming the fish, for logging fishing records, or for comparing your catch against species records. Remember that the estimate may vary from actual weight due to factors like fish condition, season, and gut content.
Frequently Asked Questions
How does the fish weight calculator work?
The fish weight calculator uses the formula weight = length × girth² / divisor, where the divisor varies by species. For Gar, Muskie, and Pike, the formula weight = length³ / 2700 is used instead. If girth is not provided, it is estimated as 58% of the length.
What measurements do I need?
You need the fish length and optionally the girth. Length is the distance from the tip of the snout to the fork of the tail. Girth is the maximum circumference around the fish body. If you only have length, the calculator estimates girth automatically.
How do I measure fish length correctly?
Measure the fish as a straight line from the tip of the snout to the fork of the tail (fork length). Do not follow the curvature of the body. Lay the fish flat on a measuring board for the most accurate measurement.
How do I measure fish girth?
Fish girth is the maximum circumference around the fish body, typically measured just in front of the dorsal fin. Use a flexible measuring tape and wrap it around the thickest part of the fish.
What if I do not know the girth?
If you do not know the girth, leave the girth field empty. The calculator will estimate the girth as approximately 58% of the fish length, which is a standard rule of thumb used by anglers worldwide.
Why does the formula change by species?
Different fish species have different body shapes. Thicker fish like sturgeon have a higher weight-to-length ratio, while slender fish like pike are lighter for the same length. Using species-specific divisors ensures accurate weight estimates.
How accurate is the estimated fish weight?
The fish weight calculator provides a close estimate but may not match the actual weight exactly. Factors like fish condition, fat content, and stomach fullness affect weight. For tournament or record purposes, always use a certified scale.