What this calculator does
Fish weight from length works out estimated fish weight from length and girth, or length alone, using standard angler formulas. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaTrout-like: W = L × G² / 900; Largemouth bass: W = L × G² / 800; Pike: W = L³ / 2700; girth (if unknown) ≈ 0.58 × L, all in inches, W in lb
The inputs explained
| Field | What to enter |
|---|---|
| Fish type | Choose from Trout-like (salmon, walleye, etc.), Largemouth bass, Pike. |
| Length (in) | A number, measured in in. Starts at 20. |
| Girth (0 to estimate from length) (in) | A number, measured in in. Starts at 0. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with length
Every other input is held at the calculator’s starting values while length varies. Select any row to load that scenario into the calculator.
How the answer changes with length
| Length (in) | Estimated weight | Girth used | In kilograms |
|---|---|---|---|
| 10 | 0.37 lb | 5.80 in (estimated from length) | 0.17 kg |
| 15 | 1.26 lb | 8.70 in (estimated from length) | 0.57 kg |
| 20 | 2.99 lb | 11.60 in (estimated from length) | 1.36 kg |
| 30 | 10.09 lb | 17.40 in (estimated from length) | 4.58 kg |
| 40 | 23.92 lb | 23.20 in (estimated from length) | 10.85 kg |
| 60 | 80.74 lb | 34.80 in (estimated from length) | 36.62 kg |