# Fish Weight Calculator

URL: https://speedycalculator.com/calculators/sports/fish-weight/
Last updated: 2026-10-30

> The fish weight calculator estimates a fish's weight from its length and girth – or length alone – with species-specific formulas for bass, trout, salmon, pike, walleye, panfish and more, so you can release your catch quickly.

## Inputs

- Species
- Custom factor k
- Length (in, cm)
- Girth (0 = estimate) (in, cm)

## Results

- Girth used
- Estimated weight

## Formula

```
Weight (lb) = length × girth² ÷ k  (inches) · k = 800 for most fish, 900 for trout and shad, 1,200 for panfish; girth ≈ 0.58 × length if not measured
```

## Explanation

Anglers who catch and release don't want to keep a fish out of the water to weigh it. A quick length and girth measurement with these formulas gives a good estimate.

### How to use the Fish Weight Calculator

- **Species**
- **Custom factor k**
- **Length**
- **Girth (0 = estimate)**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Choose the species, enter the length (nose to tail fork) and girth (around the widest part) – or leave girth at 0 to estimate it.

### Tips

- Check local conditions and safety rules before going out.
- Start with conservative equipment choices and adjust with experience.
- Every field has its own unit menu.
- Everything is calculated in your browser.

### Common mistakes to avoid

- Using estimates instead of a proper check in the water.
- Mixing feet and metres, or knots and km/h.
- Overestimating your skill in strong wind.

### Inputs explained

FieldWhat to enterSpeciesChoose one: Bass / striper, Carp, catfish, walleye, Trout, herring, shad, Salmon, sturgeon …Custom factor kA numberLengthUnits: in, cmGirth (0 = estimate)Units: in, cm

### Example values

How the main result changes when **Custom factor k** changes and everything else stays at the example values above:

Custom factor kEstimated weight (lb)4003.3646003.3648003.3641,0003.3641,2003.3641,6003.364

## Worked example

Inputs — Species: Bass / striper; Length: 20 in; Girth (0 = estimate): 0 in.

Results — Girth used = 11.6 in; **Estimated weight = 3.364 lb**.

## Key terms

- **Girth**: Circumference at the widest part.

## FAQ

**How do I measure girth?**
Wrap a soft tape around the fish just in front of the dorsal fin.

**Is the estimate accurate?**
Usually within 10–15%; spawning fish may be heavier.

**Why do panfish use a different factor?**
Their deep, flat bodies change the shape relation.

**Can I use it for records?**
No – records need a certified scale.


## Sources

- [In-Fisherman – Weight formulas](https://www.in-fisherman.com/)
- [NOAA Fisheries](https://www.fisheries.noaa.gov/)