Workshop Calculators
The Math Behinda Better Build.
BenchRoot calculators handle the repetitive workshop arithmetic — board footage, stock layouts, sheet quantities, angles, spacing and measurement conversions — directly at the bench.
Works in the browser, on a phone at the bench. Fractions like 3/4 or 1 3/8 are accepted wherever a length is asked for.
Six instruments for the bench.
Calculation index
- 01Board Foot CalculatorEstimate rough lumber quantity.
- 02Cut List LayoutLay parts out on boards or sheets.
- 03Plywood EstimatorEstimate sheet quantity from rectangular parts.
- 04Miter AngleFind the cut angle for regular multi-sided frames.
- 05Equal SpacingLay out slats, spindles or dividers evenly.
- 06Fraction / Decimal / MetricConvert common shop measurements.
Calculator 01
Board Foot Calculator.
How much rough lumber to buy. A board foot is 144 cubic inches — one inch thick, twelve inches wide and twelve inches long.
Formula
bd ft = T × W × L × qty ÷ 144
purchase = bd ft × (1 + waste %)
One board foot = 1″ × 12″ × 12″ = 144 cu in
Net board feet
21.33bd ft
Waste allowance
+0.00bd ft
Purchase quantity
21.33bd ft
(1 × 8 × 96 in × 4) ÷ 144 = 21.33 bd ft
Convert board feet
Board feet are a volume. They turn into square feet only at a known thickness, and into linear feet only at a known thickness and width. Thickness and width are optional.
- Cubic inches
- 2880cu in
- Cubic feet
- 1.67cu ft
- Square feet
- 20sq ft
- Linear feet
- needs more
- Linear feet need the board's width.
Calculator 02
Stock Cut Layout.
Lay repeated parts out on boards or on sheet goods, allowing a kerf between every cut and keeping grain-locked panels in line with the grain.
Formula
board ≥ Σ parts + kerf × (cuts − 1)
sheets: largest part first, straight cuts
Boards required
2
Parts total
138in
Waste
54in
Waste share
28.1%
Layout · 96″ boards
- Board 1A 30″ · A 30″ · B 18″ · C 12″ — offcut 5.625″
- Board 2B 18″ · B 18″ · C 12″ — offcut 47.75″
Parts are placed longest first, each on the first board with room for it and one kerf. It is an efficient layout from a fast rule, not a proven minimum: for a few parts it is usually what you would draw by hand. Hatching marks the offcut; a lighter band marks any trim.
Calculator 03
Plywood Estimator.
Estimate how many sheets a set of rectangular parts will need, from total area plus a waste allowance.
Formula
sheets = ⌈ Σ(W × L × qty) × (1 + waste %) ÷ sheet area ⌉
Raw area
46.31sq ft
With waste
53.26sq ft
Est. sheets
2
53.26 ÷ 32.00 sq ft per sheet = 1.66 → rounded up to 2
This is an area estimate. It does not account for grain direction, part orientation, kerf or exact nesting.
Blocks show area used per sheet, by part; hatching is the waste allowance.
Angles and spacing
Calculator 04
Miter Angle.
The cut for each corner of a regular frame — hexagons, octagons, picture frames.
miter = 180° ÷ n · interior = (n − 2) × 180° ÷ n
Each miter cut
30°
Interior corner
120°
Sides
6
Measured from square: set the saw to 30° and cut both ends of every piece.
Calculator 05
Equal Spacing.
Even gaps between slats, spindles, shelves or dividers, including both outside gaps.
gap = (opening − n × width) ÷ (n + 1)
Clear gap
5.6in
Centre to centre
7.6in
(36″ − 4 × 2″) ÷ 5 gaps · nearest 1/32″: ≈ 5 19/32″
Layout marks · left edge of each member, from the left side
- #15.6″
- #213.2″
- #320.8″
- #428.4″
Calculator 06
Fraction · Decimal · Metric.
Convert a shop measurement between fractional inches, decimal inches and millimetres.
Formula
1 in = 25.4 mm exactly
fractions rounded to the nearest mark
Fraction · 1/64″
5/16″
Decimal inches
0.3125″
Millimetres
7.9375mm
One inch, magnified · 1/64″ graduations
The library
Calculators by section.
Lumber and board feet
- Board Foot CalculatorWork out board feet from thickness, width and length, add a waste allowance, and convert board feet to cubic, square and linear feet where the sizes allow.
- Lumber Calculator: Pieces, Board Feet, Linear Feet and CostWork out how many boards to buy with a waste allowance, their board feet and linear feet, and the cost at your price per board foot, linear foot or piece.
- Wood Weight Calculator: Boards by Species and Moisture ContentEstimate the weight of boards from species, moisture content and size, in pounds and kilograms, from Wood Handbook specific gravities and density equations.
- Log Board Foot Calculator: Doyle, Scribner and InternationalBoard feet in a log by the Doyle, Scribner Decimal C and International ¼-inch log rules, from small-end diameter and length, with why the three rules disagree.
- Wood Movement Calculator: Shrinkage, Swelling and Moisture ContentEstimate how much a board's width shrinks or swells between two moisture contents, by species and ring orientation, with equilibrium and ovendry moisture tools.
Sheet goods
Cut lists
Angles and geometry
- Crown Molding Angle Calculator: Miter and Bevel for Any CornerCrown molding angle calculator for crown laid flat: miter and bevel from wall angle and spring angle, checked against Makita's and DEWALT's settings.
- Miter Angle Calculator: Frames and Boxes, Flat or SplayedA miter angle calculator for frames and boxes of 3 to 36 sides, flat or with sloping sides: miter and bevel, the formulas, and a chart of common settings.
Furniture sizing
- Cabinet Door Size Calculator: Overlay or Inset, One Door or a PairA cabinet door size calculator for overlay and inset doors, single or paired, from the opening and the overlays, reveals and gap you enter, in inches or mm.
- Drawer Size Calculator: Box Sizes and Drawer SpacingA drawer size calculator: drawer boxes from the opening and your slide maker's clearances, and drawer spacing for equal or graduated stacks, in inches or mm.
- Shelf Span Calculator: Estimated Shelf Sag on Two SupportsA shelf span calculator that estimates elastic sag for a shelf on two supports, loaded evenly or at the centre, from span, depth, thickness, load and E.
Measurement Reference
One inch, three ways.
The fractions that come up most at the bench, with their exact decimal and metric equivalents. 1 inch = 25.4 mm exactly.
| Fraction | Decimal inch | Millimetres |
|---|---|---|
| 1/16″ | 0.0625 | 1.5875 |
| 1/8″ | 0.125 | 3.175 |
| 3/16″ | 0.1875 | 4.7625 |
| 1/4″ | 0.25 | 6.35 |
| 3/8″ | 0.375 | 9.525 |
| 1/2″ | 0.5 | 12.7 |
| 5/8″ | 0.625 | 15.875 |
| 3/4″ | 0.75 | 19.05 |
| 7/8″ | 0.875 | 22.225 |
| 1″ | 1 | 25.4 |
Before the First Cut
Do the Math BeforeYou Cut the Wood.
A few seconds of arithmetic can save a board, a sheet or an entire glue-up.