Formulas and assumptions

Every calculator starts with measurable geometry, converts to a common unit, applies the selected allowance once, and rounds only where an order must use whole products or packages.

Area and coverage calculations

Flooring, tile, roofing, siding, insulation, drywall, decking, and paint calculations use area or linear coverage. Product counts divide the adjusted requirement by the coverage entered for one sheet, box, board, bundle, carton, package, or container, then round up.

Layout-dependent materials

Deck boards, joists, fence posts, rails, pickets, wall studs, plates, masonry units, and pavers are estimated from the dimensions and spacing entered. These are material takeoffs rather than structural designs; spans, footing sizes, fastener schedules, and assemblies must follow the chosen product, approved plans, and local requirements.

Stair rise, run, and stringer geometry

The stair calculator divides the total rise into equal risers, calculates total run from tread depth, and uses right-triangle geometry for the sloped stringer line. It is a planning aid, not a code or structural approval; verify every stair dimension, support, material, cut, connection, landing, guard, and handrail requirement before construction.

Board feet and sheet goods

Board-foot volume uses the actual dimensions and quantity entered, without a waste factor, and price is volume multiplied by the seller's rate per board foot. Plywood and other sheet-goods counts divide waste-adjusted coverage area by one sheet's area and round up; a physical cut layout may require more sheets than an area calculation.

Ramp slope and roof pitch

Ramp grade is rise divided by run as a percentage. Roof pitch normalizes the same ratio to 12 units of run, while the roof slope factor converts horizontal projected area to sloped surface area. These geometry results do not establish code compliance or structural adequacy.

Bulk materials

Mulch, gravel, topsoil, paver base, and bedding sand are converted to cubic feet, cubic yards, and cubic meters. Weight estimates also multiply volume by the user-selected bulk density because density varies by material, moisture, grading, and compaction.

Concrete calculations

Rectangular volume

All three dimensions are converted to feet before multiplication. A thickness entered in inches is divided by 12; metric dimensions are converted with exactly 1 inch = 25.4 millimeters.

Cylindrical and post-hole volume

Order quantity and conversions

• 1 cubic yard = 27 cubic feet.
• 1 cubic foot = 0.028316846592 cubic meters.
• Bag counts always round up to the next whole bag.

Packaged-mix yields

The current general-purpose mix assumptions are 0.30 ft³ per 40 lb bag, 0.45 ft³ per 60 lb bag, and 0.60 ft³ per 80 lb bag. These approximate yields match published manufacturer data for a common general-purpose mix, but the label on the selected product controls.

Cost estimates

Ready-mix cost equals waste-adjusted cubic yards multiplied by the price entered per cubic yard. Bag cost equals the rounded bag count for the selected size multiplied by the entered price per bag. Delivery, short-load fees, tax, labor, reinforcement, forms, excavation, finishing, and equipment are not added unless explicitly stated.

Review and corrections

Calculator behavior is checked with automated examples, boundary values, and unit-conversion tests. When an assumption comes from a manufacturer or standard, the page identifies the source or tells the user which product-specific value to enter. To challenge an assumption or report a reproducible error, use the contact and corrections page.