Calculator shelf

Home Project Calculators

Roof has a interactive calculator; other home-project calculators are available as planning aids with examples, assumptions, and source notes.

Updated June 24, 2026Planning aidVisible assumptions

Availability

Use listed tools as planning aids and read each page's formula, example, assumptions, and limits.

Start here paths

Start with the roof calculator; treat structural and cost pages as planning aids and compare results with local requirements.

Convert footprint and pitch into surface area, roofing squares, bundles, and material basis.

Interactive calculator.

Estimate gallons from impervious area, rainfall depth, and runoff coefficient before sizing barrels or drainage.

Planning aid; local drainage rules still matter.

Estimate added psf from panels and hardware, then require installer or engineer review before acting.

Safety-sensitive planning aid.

Home Projects · Energy

Estimate holiday string-light kWh and energy cost from label wattage, timer hours, display days, and entered utility price.

Interactive calculatorOpen calculator

Estimate roof area, exterior runoff, flat-roof cost, and load assumptions from measurements before quoting materials.

Convert a flat house footprint into pitched roof area, roofing squares, bundles, waste, and material basis.

Interactive calculator · Updated 2026-06-24

Estimate runoff volume and rain-barrel count from roof area, impervious area, rainfall, and runoff coefficient.

Planning aid · Updated 2026-06-24

Build early project ranges for additions and loft conversions before requesting contractor estimates.

Compare the calculator inputs with your measurements, then read the formula, example, assumptions, and limits before using the estimate.

Estimate insulation bags, solar panel counts, and roof-load checks from area and usage assumptions.

Compare the calculator inputs with your measurements, then read the formula, example, assumptions, and limits before using the estimate.

Turn room, walkway, mesh, pipe, stair, and board measurements into material counts and layout checks.

Calculate travel length and setback for a pipe offset from angle and offset distance.

Planning aid · Updated 2026-06-24

Each calculator states its formula or method, shows an example, and lists assumptions that can change the result.
Specialized planning calculators remain accessible, while broad recommendations emphasize the clearest calculators.
Safety-sensitive tools show conservative warnings and assumptions.