How we calculate.

Every calculator on this site runs on one geometry engine. It holds all dimensions in millimeters 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. Its scope is residential home improvement and nothing else: materials, layouts and project costs for the floors, tile, walls, wallpaper and windows of a house.

Millimeters inside, sixteenths outside

Internally there are no inches and no fractions, only millimeters 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. Running lengths and areas — linear feet, yards, meters, square feet — print as decimals, to the precision shown beside each figure.
• 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.

The spray foam cost estimate counts one quantity, the board foot: one square foot sprayed one inch deep. Its thickness is the target R-value divided by an R per inch the reader can overwrite, it is compared with the dressed depth of the framing, and the price per board foot stays an input because no public source publishes one. Its zone levels and R per inch are dated in the sources box of that page.

The window replacement quote comparison divides each bid twice: by the windows it covers and by the square feet of opening on the reader's list, width times height over 144. A line left blank on a bid is reported as not stated, never as zero, and the per-square-foot figure is withheld when a bid covers fewer windows than the list.

The driveway bid comparison adds the zones of a drive as plane figures: a rectangle, a flare as the mean of its two widths times its depth, a turnaround as π × diameter² ÷ 8. Each bid's all-in total is divided twice, by the area the bid states and by the area measured, and a paver bid's base and bedding sand are read against ICPI Tech Spec 10. No volume or weight of material is computed.

The shower bid comparison treats every itemized line as part of its bid's total, never as an extra. A line one bid states and another leaves blank is taken out of the first before the totals are compared, a blank is reported as not stated rather than zero, and the floor and wall areas come from inside dimensions, three walls to one tiled height, with the open front left out.

The chimney repair worksheet reads two code rules before any price: the height the stack must clear above the roof and nearby parts of the building, and the chimney width that calls for a cricket. The masonry face above the roof is measured from the stack, and every repair rate stays an input taken from the reader's quote.

The basement waterproofing worksheet measures the foundation wall from finished grade down to the depth the code's waterproofing section sets, subtracts openings below grade, checks a quoted membrane against the materials listed for the selected edition, and reads the soil group to say whether a footing drain is required.

The attic insulation price check multiplies the attic floor by each rate you enter, keeps a blank line apart from a line priced at zero, compares the installer's receipt with the items the federal R-value rule lists, and sizes the net free vent area at 1/150 of the floor, or 1/300 when both code conditions for the reduced ratio are confirmed.

The basement finishing worksheet checks an escape window and its area well against the IRC opening rules, measures the ceiling height left under beams and ducts after the floor build-up, takes the wall R-value from the cell of your climate zone without interpolating, and prices each line of your own finishing quote.

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.

The same calculations, for AI assistants

Four of these calculations also run as a remote Model Context Protocol (MCP) server named Calculiva Cut Planner, at https://mcp.calculiva.com/mcp (Streamable HTTP, no account, no key). An assistant that accepts remote MCP connectors can call it and get cut lists and order quantities that were computed, not guessed.

• plan_flooring_order: laminate, vinyl or engineered plank flooring for 1 to 12 rooms, rectangles or L shapes. It returns the cartons to buy, every cut piece traced to its source plank, offcuts carried from one room to the next, and eight layout scenarios side by side — the multi-room version of the one-room plank layout.
• plan_trim_order: board and batten, wainscoting or picture frame molding on one wall, with the spacing, the cut list and the boards to buy at each retail length.
• plan_wallpaper_order: the rolls to buy from the walls, doors, windows and roll label, each drop placed on its roll, with straight, half-drop and random matches compared, as on the roll-by-roll wallpaper plan.
• build_order_sheet: one order for the whole project, with the trim pieces of every wall packed together on the stock boards, compared with ordering wall by wall, and a CSV.

The server only computes. It keeps no record of the measurements it receives and answers each request on its own; every answer links back to the matching calculator on this site.