Estimate Fish Weight from Length (W = aL^b)

Estimate weight (g/kg/lb) from length (cm/in). Save/share coefficients a,b, run batch calculations, and back-solve coefficients from samples.

Internal calculation uses cm and g. Inches are auto-converted; output units can be switched anytime.

W=aL^b Save/Share Batch Back-calc

داخل شوي معلومات

Calculate and save on one screen

Optional. Internal names are fine.

Match the coefficient basis

Coefficients (a, b)

Confirm source and assumptions (cm TL) before use.

حواله

0 < a

1 < b < 5 is typical

Coefficient basis:
%

Adjust for regional/seasonal variation (guideline)

Additional features

Open only if needed

Estimation helpers

  • Recalculates on input changes (button stays, but updates are live)
  • Pin saved coefficients at the top
  • One-click copy for results

Presets (reference)

Confirm source and assumptions (cm TL) before use.

Japanese horse mackerel (Trachurus japonicus)

a=0.01096, b=2.97 / TL

FishBase (Bayesian length-weight)

Chub mackerel (Scomber japonicus)

a=0.00741, b=3.05 / TL

FishBase (Bayesian length-weight)

Japanese flounder (Paralichthys olivaceus)

a=0.00794, b=3.07 / TL

FishBase (Bayesian length-weight)

Japanese seabass (Lateolabrax japonicus)

a=0.01259, b=3.02 / TL

FishBase (Bayesian length-weight)

Red sea bream (Pagrus major)

a=0.01288, b=3.03 / TL

FishBase (Bayesian length-weight)

Black seabream (Acanthopagrus schlegelii)

a=0.02138, b=2.99 / TL

FishBase (Bayesian length-weight)

Mode A: assume b and solve for a

Estimated a

فارمول: a = W / L^b

Mode B: fit a,b from multiple data points

L W

Fit results

a:
b:
R²:
Error % (suggested):

Fit with least squares on log(W) = log(a) + b log(L)

Set coefficients at the top. Enable per-row coefficients if needed.

Species اوږدوالی Estimated weight Range min Range max عملونه

Save & share

Shows “shortening not supported” if URL is too long

Example JSON schema

{
  "version": "1.0",
  "baseUnits": { "length": "cm", "weight": "g" },
  "coefficients": [
    {
      "id": "myset-001",
      "name": "PlantA_RedSeaBream_2026Spring",
      "species": { "common": "Red sea bream", "scientific": "Pagrus major" },
      "lengthType": "TL",
      "a": 0.01288,
      "b": 3.03,
      "defaultErrorPct": 20,
      "source": { "label": "FishBase (Bayesian length-weight)", "url": "https://fishbase.se/Summary/SpeciesSummary.php?id=445&lang=japanese" },
      "notes": "Adjust by region/season"
    }
  ]
}

یادښتونه

  • This estimate is a guideline. Results vary widely by region, season, maturity, and measurement type (TL/FL/SL).
  • Use coefficients with the same length type and unit basis.

よくある質問

I don't know a and b

In the “Unknown coefficients” tab you can (1) back-solve a from one sample with assumed b, or (2) fit a,b from multiple data points.

I want to calculate multiple individuals

Use the “Batch” tab to enter a table or paste CSV. You can download results as CSV.

Can I switch cm/in and g/lb?

Yes. Length and weight units can be switched anytime (internal calculation uses cm and g).

Why is the error large?

Even within a species, weight varies by region, season, body condition, and age. Viewing estimates as a range is recommended.

اړوند اوزار

Length–weight calculator for fish (W=aL^b). Save/share coefficients as JSON.