Shop math, sourced and explained.
Woodworking calculators and wood reference, every number sourced
Woodworking Math is a free reference for the shop: wood species, finishes and glue, joinery, lumber and plywood, tools and machines, fasteners and drilling, with a calculator wherever there is math to do. Every number says where it came from: the median of three or more published sources when they exist, both sources named when only two print it, and no answer at all when the sources are not there. We would rather refuse than guess.
Find your way in
- WoodSpecies and wood types: hardness, weight, movement, color and what each is good for.
- FinishingFinishes, glues and fillers: dry and cure times, which to use, and how they compare.
- JoineryJoints and how to size them: dovetails, mortise and tenon, rabbets, dadoes and more.
- Lumber & plywoodBoard feet, actual and nominal sizes, hardwood quarters, plywood sizes and grades.
- Tools & machinesSetup and choice for the table saw, miter saw, router, planer, jointer, lathe and CNC.
- Fasteners & drillingScrew sizes, pilot and clearance holes, countersinks and drill bit sizes.
Calculators
- Wood movement calculatorHow much a board will swell or shrink, by species, width and grain, from moisture content or temperature and humidity, by USDA Wood Handbook data.
- EMC calculatorThe moisture content wood settles at for a given temperature and relative humidity, by the USDA Wood Handbook equation, with its full EMC chart.
- Wood weight calculatorWhat a board or a stack of lumber weighs, by species and moisture content, worked from USDA Wood Handbook specific gravity. In lb or kg, live as you type.
- Shellac cut calculatorHow many ounces of shellac flakes for a 1, 2 or 3 lb cut, and how much alcohol thins a premixed 3 lb can to the cut you want. Sourced and shown.
- Finish coverage calculatorHow much polyurethane, lacquer, oil or stain a job takes, from each maker’s own coverage rate or the range across makers. Sq ft or m², any coats.
- Dovetail calculatorLay out dovetails for any board: tail and pin widths on both faces, marks from the edge, and the slope as a ratio or an angle (1:6, 1:8).
- Box joint calculatorFinger joint spacing that fits your board: how many fingers a dado stack or bit gives, the leftover, and the even width for an adjustable jig.
- Mortise and tenon calculatorTenon thickness for your stock by the one-third rule, rounded to a mortise chisel you can buy, with the shoulder on each cheek. Inches or mm.
- Board foot calculatorBoard feet for a stack of lumber: several sizes at once, cost per board foot, overage, metric, and the hardwood yard’s NHLA tally rules.
- Log board feet calculatorBoard feet in a log by the Doyle, Scribner Decimal C and International 1/4-inch log rules, side by side, from the small-end diameter and length.
- Miter and crown angle calculatorMiter and bevel settings for picture frames, polygons, any corner, crown molding laid flat or nested, and sloped-sided boxes. Geometry, shown step by step.
- Five-cut sled calculatorEnter the two ends of your five-cut test strip and get the fence error per foot, the angle and how far to move the fence. Inches or millimetres.
- Cuts per inch calculatorCuts per inch for a thickness planer or jointer from cutterhead RPM, knives and feed rate, checked against the figure each planer's maker states.
- Router bit speed calculatorMaximum router speed for a bit's diameter: the median of four makers' charts, never above the speed marked on the bit. Chart from 1/4 in to 3 1/2 in.
- CNC feeds and speeds calculatorFeed rate for a CNC router bit in softwood, hardwood, MDF or plywood from the median of bit makers' chip loads, with the depth-of-cut step. Inches or mm.
- Wood lathe speed calculatorWood lathe speed for roughing, general cutting and finishing by blank diameter, the median of three lathe makers' charts, with rim speed shown.
- Forstner bit speed calculatorDrill press speed for a Forstner bit by diameter, in hardwood or softwood, from a bit maker, a drill press maker and Fine Woodworking, each figure shown.
- Pilot hole calculatorThe pilot hole for a wood screw in hardwood or softwood, with the clearance hole and countersink: the median of the published charts, in inches and mm.
- Countersink depth calculatorHow deep to drill a countersink so a flat-head screw sits flush or below the surface: head diameter, 82°, 90° or 100° bit, and a combination bit’s pilot.
How it works
Each number carries a small source tag: three marks when three or more sources agree, two when only two publish the figure, one when a single source is the authority for it, such as the maker of that exact product. A shop rule that was never measured is labelled as a traditional rule and names the references that state it. Open "Why these numbers?" under any result to see the reasoning step by step, and read how we source for the whole method.
It works on a phone at the bench and on a desktop, in a light or dark theme, and keeps working with no signal once you have opened the site. Nothing you type leaves your device.