How we calculate.

Every calculator on this site runs on one geometry engine. It holds all dimensions in millimetres at full precision, rounds only when it prints, and counts pieces by cutting real polygons against real boundaries rather than dividing one area by another.

Millimetres inside, sixteenths outside

Internally there are no inches and no fractions, only millimetres in double precision. Switching a page between imperial and metric does not re-read your measurement, so nothing drifts: type 12 3/8", switch to metric and back, and you still have 12 3/8 inches rather than 12.375 rounded twice.

On screen the numbers come back in sixteenths of an inch, reduced — 18 3/16", not 18.1875 in and not 18 6/32". A value smaller than a sixteenth prints as < 1/16" rather than collapsing to zero.

Pieces are cut, not estimated

Where a layout meets a boundary, each piece is clipped against that boundary and the remaining polygon is kept with its own vertices. Nothing is inferred by dividing a surface by a piece size. An independent geometry library was used to check that the pieces tile the space exactly and do not overlap, across five patterns and thirty configurations.

What we round, and what we never round

• Displayed dimensions are rounded to the nearest 1/16 inch, or 0.1 mm in metric.
• Quantities are rounded up, always. A part board is a board.
• Angled pieces are reported by their bounding box in tables; the true vertices are in the CSV.
• The geometry itself is never rounded. Rounding happens at the last step, on the way out.

What the engine does not model

• Rectangular spaces without obstacles, unless a page says otherwise.
• Offcut reuse is excluded unless a tool explicitly provides a source-piece allocation.
• Cutting plans are workable, not proven optimal, and they say so on the page.
• Walls are assumed flat and square. They are not.
• Product tolerances, movement joints and installation standards are outside the model.

A calculator that hides its assumptions is asking to be trusted. One that prints them can be checked. That is the whole difference, and it is why every page carries a limits section.

Where the numbers come from

The flooring source-board schedule can pair a starter and an end cut on opposite factory ends of one plank. It reserves two crosscut kerfs and keeps both destinations traceable; it does not claim a globally optimal cutting plan.

The wall opening calculation intersects a window with the tiled-height range. Only that overlap leaves the wall field; selected return surfaces enter the count separately.

The ceiling panel comparison shows how rotating the same rectangular module changes perimeter cuts. Complete cells reserved for fixtures remain on the drawing but leave the panel purchase count.

The tile layout and cutting calculator makes polygon clipping visible: inspect an individual piece, then compare its discarded material with the separate reserve and carton-rounding entries in the purchase ledger.

No board width, roll size or coverage figure is written into the code. Each one lives in a register with its source, its status and the date it was last verified — see data and sources. The first tool built on all of this works out even batten spacing and the boards to buy.