Fish Weight Calculator

Estimate a fish's weight from length and girth.

Length

Girth

Estimated weight 3.6

Estimated weight 1.633

Formula: weight (lb) = length × girth² ÷ 800

Step-by-step with your numbers:

1. Values used:

2. Length = 20

3. Girth = 12

5. Estimated weight = 3.6

6. Estimated weight = 1.633

Did we solve your problem today?

Estimate a fish's weight without a scale, using length and girth.

The math behind it

weight (lb) = length × girth² ÷ 800 (a common formula for many species).

20 in long, 12 in girth → 3.6 lb.

Species vary?

Yes — slender fish use ÷900, fatter ones ÷700.