KerfMath: Computed, Not Guessed

Why this site exists

Most woodworking calculators online are ad-heavy single-purpose pages: one page for board feet, a different site entirely for wood movement, a third for miter angles, none of them linked, none of them sharing a species or dimension reference. That fragmentation is the actual problem this site solves — not by building a smarter board-foot calculator (the math is the same math everywhere), but by building a coherent, linked set of tools that all read from the same real species and dimension data, so a number you get from one calculator agrees with the reference pages around it.

What's actually here

Five calculators cover the arithmetic that comes up on nearly every project: board feet and lumber cost, a cut-list optimiser that lays out pieces to minimize waste and draws the layout to scale, wood movement (the calculation most likely to prevent a ruined build), miter and compound-bevel angles for flat frames and sloped work, and finished weight. Behind them sits a reference layer — a page per common wood species with real density, hardness, and movement figures; a joinery reference covering roughly forty real joints with the numbers behind why each one holds; and a dimension and conversion reference covering everything from nominal-vs-actual lumber sizes to sandpaper grit progression.

Why "computed, not guessed"

Every number on this site that looks like an answer either came out of one of the five tools or was checked against it before publishing. Wood movement in particular is the calculation most woodworkers either skip entirely or approximate with a rule of thumb that doesn't account for species, board width, or the actual humidity swing involved — and it's the single most common cause of a cracked panel or a jammed drawer months after a project looked finished. Guessing at that number, or copying a generic "wood moves about a quarter inch" rule from a forum post, is exactly the failure mode this site is built to avoid.

Who this is for

Anyone who wants a real answer instead of a rule of thumb: a hobbyist sizing their first dovetailed box, someone buying rough lumber for the first time and trying to understand what the yard is actually charging for, or an experienced maker who wants to double-check a compound miter angle before committing an expensive piece of stock to the saw. The tools assume no special software or account — enter numbers, get an answer, and the URL updates as you go so you can bookmark or share the exact result.

Most-used starting points

If you're not sure where to start: the board foot calculator is the single most useful tool for pricing out a project before you buy material, the wood movement calculator is worth running on any wide panel or breadboard-end design before you cut, and the species reference is the fastest way to compare two candidate woods on hardness, movement, and typical cost before committing to one.

FAQ

Do I need to create an account? No — every tool runs entirely in your browser, and results are shareable via the URL rather than a saved account.

Where do the species numbers come from? Density, hardness and movement figures are sourced from published reference data (USDA Forest Products Laboratory and equivalent citable sources) and cited per species — see each species page for its specific source.

Is the cut-list optimiser guaranteed to find the mathematically perfect layout? No — it uses a fast, well-understood packing heuristic (first-fit-decreasing) that typically lands within a few percent of the theoretical minimum waste, and is explainable and deterministic rather than a black box.

Can I use this for a paying job, not just a hobby project? Yes — the tools and reference data are free to use for any project. The Shop Reference Pack is a separate, optional printable PDF for anyone who wants the core tables at the bench without a screen.

A note on accuracy

Wood movement figures in particular are the one dataset on this site where a wrong number can genuinely ruin a piece of finished work — a shrinkage coefficient that's off by even a small margin compounds across a wide panel into a real, visible gap or crack. Every species entry states its source, and the movement math itself (ΔD = D x ΔMC x C, where C is derived from the species' published shrinkage percentage and the fiber saturation point) is documented and tested rather than hidden inside a black-box widget — see the wood movement will destroy your build post for the full arithmetic worked through a real example.