Everything you might want to know about Fishing Toolbox — our tools, how accurate they are, and how we build them.
Is Fishing Toolbox really free?
Yes. Every calculator and guide on the site is free to use. There’s no sign-up, no account, and no app to download — just open the tool in your browser and go. The site is supported by ads, which is what keeps the tools free for everyone.
Do I need to create an account or log in?
No. Nothing on Fishing Toolbox requires an account. All the calculators run right in your browser, including on your phone at the water.
How accurate is the fish weight calculator?
When you enter both length and girth, the calculator is typically accurate to within 5–10% of a certified scale — good enough for catch-and-release records, slot-limit decisions, and settling bets at the ramp. Length-only estimates (like our charts) are less precise, because two fish of the same length can differ in weight by 20% or more depending on how well-fed or egg-heavy they are. For the closest number, always measure girth too.
What formula do you use to estimate fish weight?
For most species we use the standard length-and-girth formula:
Weight (lb) = Length × Girth² ÷ 800
(with length and girth in inches). Some long, slender species use a slightly different divisor. Our species length-to-weight charts use length-only formulas — for example, walleye use length³ ÷ 2,700 and northern pike use length³ ÷ 3,500 — matched to published fisheries data.
Why is my fish’s actual weight different from the chart?
Charts show an average for a fish in typical condition. Your fish can be heavier or lighter because of the spawn (pre-spawn females are the heaviest of the year), how much it’s been eating, its body depth, and regional genetics. That’s why girth is the single best predictor of true weight — measure it and use the fish weight calculator for a number tailored to your exact fish.
How do I measure a fish’s girth?
Wrap a soft (cloth or fabric) tape measure around the fattest part of the fish’s body, just behind the pectoral fins, and read the measurement in inches. If you only have a stiff tape, a piece of string works — wrap it, mark it, then measure the string. Our guide on how to estimate a fish’s weight walks through it step by step.
Can I use the tools on my phone?
Yes — the calculators are designed to work on a phone browser right at the water, with no app to install.
Do the tools work for saltwater fish?
The length-and-girth weight formula works for many species, fresh and salt, though the best divisor varies by body shape. Our length-to-weight charts currently focus on popular North American freshwater gamefish and panfish, and we’re adding more over time.
Who writes and checks the content?
Fishing Toolbox is founded and run by Matt Bush, a lifelong angler. Tools are built on established angling formulas, and species facts are checked against authoritative sources like the IGFA and state DNR fisheries agencies. Read more on our About page.
I found a number that looks wrong. How do I report it?
Please tell us — accuracy is the whole point. Send a note via the contact page with the tool or chart and the fish details, and we’ll take a look.
Can you add a calculator or species I don’t see?
Very possibly. We’re always expanding the toolbox. Send your request through the contact page and tell us what you’d find useful.