About PaintingCalcs
PaintingCalcs is an independent project with one goal: to gather the everyday calculations homeowners, DIYers and small painting contractors reach for when a room, a house or a set of cabinets gets painted — paint quantity & coverage, interior and exterior cost estimators, whole-house & project cost, cabinets & specialty surfaces, and paint selection & planning — in one focused, free, no-signup hub with transparent formulas, so you can budget a paint job and sanity-check a painter’s quote.
Who is behind it
Author and curator
To be clear about credentials: I am the author and curator of this site — not a licensed painter, a painting contractor or any trade professional, and I claim no trade credential. What I bring is relevant and real: building deterministic online calculators (open-source Python projects) and electronic-engineering training (Systems Theory, Sapienza University of Rome). Paint quantity is plane geometry (paintable area = wall perimeter × height − openings; gallons = area × coats ÷ coverage-per-gallon) and paint cost is a quantity × unit-price sum (cost = area × $/sq ft or gallons × paint price + labor + add-ons) — the same rigorous arithmetic I apply in systems and electronics, so the math of these calculators is squarely in my competence, while surface-prep judgement (moisture, adhesion, pre-1978 lead-safe abatement, structural repairs) is explicitly deferred to licensed pros, the EPA RRP rule and the manufacturer’s data.
Our principle: transparent & durably correct
Every calculator shows its formula, a worked example and a reference table. The tools rest only on timeless paintable-area geometry (wall area = perimeter × height; net area = gross − openings; ceiling = L × W; gallons = ceil(area × coats ÷ coverage); primer = ceil(area ÷ primer coverage); cost = area × your $/sq ft + labor + add-ons, ×(1 + contingency)) and stable, labeled conventions (coverage per gallon by paint & surface, primer coverage, coats by scenario, door/window deductions, cost bands). There are deliberately no live material or labor prices, no regional cost indexes, no product catalog and no contractor directory — cost tools use the prices you enter — so the results stay valid over time.
Correctness is checked against known reference values (see the methodology and the numeric self-check). The formulas and their basis are documented under Sources & formulas. All results are planning estimates and paint quantity / coverage guides: get itemized written quotes from licensed, insured painters, measure your actual surfaces and confirm coverage on the paint can, and allow extra for texture, porosity, color change and waste. Professional surface prep, lead-paint abatement, structural repairs and code compliance are out of scope and are for the EPA RRP rule, local code and a certified professional. Questions? Use the contact page.