Fishing Toolbox is a free set of fishing calculators and plain-English guides built by anglers who’d rather run the numbers than guess. It started with a simple frustration: doing the same quick math by hand at the boat ramp over and over — estimating a fish’s weight, dialing in drag, working out how deep a lure was running. So we put the calculations we actually use into one free, no-login place that works on your phone right at the water.
Everything here is free. No sign-up, no app to download, no paywall. Our calculators are built on established, widely-used angling formulas, and our guides explain the how and why behind them so you can fish smarter, not just harder.
Who’s behind it
Matt Bush is the founder of Fishing Toolbox. A lifelong angler with a soft spot for the math behind the sport, he built the site’s calculators to answer the everyday questions that come up on the water — how much a fish weighs, where to set the drag, how deep a lure is running — so anglers can spend less time guessing and more time fishing. When he isn’t refining a formula, he’s on the water putting it to the test.
Matt writes and reviews the guides and tools on the site. Have a question, a correction, or a tool you’d like to see? Reach him on the contact page.
How we build our tools (and where the numbers come from)
We don’t make up formulas. Our calculators use the same length-and-girth and length-only equations that fisheries biologists and long-running publications rely on:
- The fish weight calculator uses the standard length-and-girth formula (Weight = Length × Girth² ÷ 800 for most species), which typically lands within 5–10% of a certified scale.
- Our length-to-weight charts are built from published, species-specific data and the length-only formulas commonly cited by In-Fisherman and state fish & wildlife agencies (DNRs).
- Species facts — sizes, records, habitat, spawning — are checked against authoritative sources such as the IGFA world-record database, state DNR species profiles, and university extension resources.
A calculator is only as trustworthy as its math, so if a number ever looks off to you, tell us — we’d genuinely like to know.
What you’ll find here
A fish weight estimator, a reel line capacity calculator, a drag-setting tool, a trolling depth estimator, a sunrise/sunset bite-window finder, a water-temperature species guide, and handy unit converters — plus a growing library of how-to guides and species length-to-weight charts.
We’re anglers first and number-crunchers second (okay, maybe it’s a tie). Tight lines.