Fish Weight Calculator
Estimate weight from length and girth, then see how your catch compares to the world record.
Quick answer: Measure total length in inches and girth at the widest point. Most bass and trout estimates use (length × girth²) ÷ 800. Pike uses ÷ 900. Results are field estimates only—not certified record weights.
Standard bass formula: (length × girth²) ÷ 800
of the 22.25 lb largemouth bass world record
Montgomery Lake, Georgia / Lake Biwa, Japan
View species guide →Species calculators
Estimate largemouth or smallmouth bass weight from length and girth, then compare your catch to the world record.
Estimate trout weight from length and girth for rainbow, brown, brook, and related stocked trout.
Estimate walleye weight from length and girth and compare it to the world record.
Estimate northern pike weight from length and girth and compare it to the world record.
How to calculate fish weight
How do you calculate the weight of a fish?
The most common recreational method multiplies length by girth squared, then divides by a species constant (often 800 for bass and trout, 900 for pike). Length-only formulas are used when girth is unavailable. Estimates are approximate and not official for records.
Is a length-and-girth calculator accurate?
It is a useful field estimate for comparing fish of similar body shape. Condition, stomach contents, and species variation affect true weight. Use a certified scale for official records.
Which species does this calculator support?
Bass, trout, walleye, and northern pike, with species-specific formulas and world-record comparisons. Open a species page for stocking and catching context.