Fish Weight — Length & Girth Estimation
General: L³/800. Bass: L×G²/1200, trout: L³/1600, pike: L³/3500. 22 lb record bass. 1200+ IGFA species. Species-specific K values.
Why This Stat Matters
Why: Catch-and-release: estimate weight without scale. IGFA uses length for records. Species-specific formulas more accurate.
How: Enter length and girth. Choose species (general, bass, trout, pike, walleye, catfish). Get estimated weight in lb and kg.
- ●L³/800 general; bass L×G²/1200
- ●22 lb record largemouth bass
- ●1200+ IGFA species with formulas
📋 Quick Examples — Click to Load
📊 Species Constants
K value by species
📈 Length vs Weight
Bass vs trout (lb)
🍩 Formula Constants
K by formula type
📊 Typical Records
Record weights (lb)
For educational and informational purposes only. Verify with a qualified professional.
🏅 Sports Records
22 lb record largemouth bass
General formula: L³/800; bass L×G²/1200
1200+ IGFA species with length-weight formulas
Fish weight = Length³ × Girth² / 800 (general). Species-specific: bass = L×G²/1200, trout = L³/1600, pike = L³/3500. World record bass 22 lb. IGFA tracks 1200+ species. Use length and girth for best accuracy; release without weighing.
Sources: IGFA, State fish & wildlife agencies, In-Fisherman.
Key Takeaways
- • General: Weight = L³ × G² / 800. Bass: L×G²/1200. Trout: L³/1600. Pike: L³/3500.
- • 800 is the general constant; species vary (1200 bass, 1600 trout, 3500 pike).
- • World record largemouth bass: 22 lb 4 oz (1932).
- • IGFA tracks 1200+ species with length-weight data.
Did You Know?
How Does Fish Weight Estimation Work?
The General Formula
Weight = Length³ × Girth² / 800. Assumes fish volume scales with L³ and cross-section with G². 800 is empirical for "average" fish.
Species Constants
Bass (1200) stockier; trout (1600) slimmer; pike (3500) very elongated. Lower K = heavier for same length. Some formulas use L×G², others L³ only.
Accuracy
With girth: ±5–10%. Length-only: ±10–20%. Condition (fat/lean) matters. IGFA and state agencies provide species-specific constants.
Expert Tips
Species Formula Comparison
| Species | Formula | Constant |
|---|---|---|
| General | L³×G² | 800 |
| Bass | L×G² | 1200 |
| Trout | L³ | 1600 |
| Pike | L³ | 3500 |
Frequently Asked Questions
How is fish weight estimated from length?
General formula: Weight = Length³ × Girth² / 800. Species-specific: bass = L×G²/1200, trout = L³/1600, pike = L³/3500. Girth is the fattest circumference. More accurate with both length and girth.
What is the L³ formula?
Weight ∝ Length³ assumes similar body shape. The constant (800 general, 1200 bass, 1600 trout, 3500 pike) adjusts for species body density. L³/800 is a rough estimate without girth.
Why does the 800 constant vary by species?
Bass are stockier (1200), trout slimmer (1600), pike very elongated (3500). The constant reflects body shape and density. Rounder fish need lower constants.
What is the world record bass weight?
22 lb 4 oz (10.09 kg) largemouth bass, George Perry 1932. IGFA and state agencies track records. 1200+ species in IGFA database.
How accurate are length-weight estimates?
With girth: typically within 5–10%. Length-only: 10–20% error. Condition (fat vs lean) affects accuracy. Release without weighing—use the formula.
Which species have the best formulas?
Bass (L×G²/1200), trout (L³/1600), pike (L³/3500) are well-studied. IGFA provides constants for 1200+ species. Check state wildlife agencies for local formulas.
Key Statistics
Official Data Sources
⚠️ Disclaimer: This calculator is for educational purposes only. Estimates vary by condition, species strain, and measurement technique. Release fish without weighing when possible. Not professional fishing advice.