Fish Weight Calculator
Estimate fish weight from length and girth measurements for different fish species
Calculate Fish Weight
Popular game fish, chunky body
Measure from tip of snout to where tail fin starts (standard length)
Leave unchecked to estimate girth automatically (girth = length × 0.58)
Fish Weight Estimate
Formula used: length × girth²/800
Measurements: Length: 0.0 cm, Girth: 0.0 cm (estimated)
Species: Largemouth Bass
Measurement Tips
Measure length as a straight line from snout to tail base
Girth is the maximum circumference around the body
Use a flexible measuring tape for best accuracy
Estimates are approximate - actual weight may vary
Example Calculations
20-inch Trout
Length: 20 inches (50.8 cm)
Estimated girth: 50.8 × 0.58 = 29.5 cm
Formula: length × girth²/900
Weight: 50.8 × (29.5)²/900 ≈ 49.4 cm²/900 ≈ 3.0 lbs
27-inch Largemouth Bass
Length: 27 inches (68.6 cm)
Estimated girth: 68.6 × 0.58 = 39.8 cm
Formula: length × girth²/800
Weight: 68.6 × (39.8)²/800 ≈ 135.6 cm²/800 ≈ 8.3 lbs
30-inch Pike
Length: 30 inches (76.2 cm)
Formula: length³/2700 (girth not needed)
Weight: (76.2)³/2700 ≈ 442,097/2700 ≈ 10.0 lbs
Fish Species Formulas
Largemouth Bass
length × girth²/800
Trout
length × girth²/900
Pike/Muskie
length³/2700 (girth optional)
Walleye/Salmon
length × girth²/950
Fishing Tips
Use a bump board or measuring tape for accurate length
Soft measuring tape works best for girth measurements
Take photos for documentation before release
Digital scales provide most accurate weights
Keep fish in water during measurement when possible
Practice catch and release for conservation
Understanding Fish Weight Calculations
How Fish Weight Formulas Work
Fish weight estimations are based on mathematical relationships between length, girth, and species-specific body density. Different fish species have different body shapes and proportions, requiring unique formulas.
Two Main Formula Types
Length + Girth Formula
weight = length × girth²/coefficient
Used for most species (bass, trout, salmon)
Length-Only Formula
weight = length³/coefficient
Used for long, slender fish (pike, muskie)
Accuracy and Limitations
- •Formulas provide estimates within ±10-20% accuracy
- •Fish condition and season affect actual weight
- •Spawning fish may weigh significantly more
- •Regional variations in body proportions exist
Best Practices
For tournament fishing or scientific purposes, use certified scales. These formulas are excellent for quick estimates, catch documentation, and when scales aren't available.