A square footage calculator that takes accuracy seriously.
We're a small editorial team that builds free, no-signup calculators and reference guides for homeowners, contractors, and DIYers. This page explains who we are, what we do, where our numbers come from, and — just as importantly — what this tool isn't for.
Why this site exists
Most square footage calculators online have at least one of these problems: no feet-and-inches input, no waste factor, no irregular shapes, no unit conversion, no material breakdown, or one shape locked to one page. We built this site to solve all of those in a single tool, then surrounded it with the kind of plain-English measurement guidance most calculator pages skip.
Every calculator on the site is free, runs entirely in the browser, requires no signup, and stores no personal data.
Who builds and reviews the content
The site is produced by an editorial team rather than a single named expert. Content is written by team members with backgrounds in residential construction estimating and technical writing, then reviewed against published industry standards before publication. We don't claim individual professional licenses, certifications, or contractor credentials — because the trust signal that matters here is the methodology, not a name.
For the full sourcing, review, and update process, see our editorial standards page.
Where our numbers come from
Every formula and coverage rate on the site traces back to a verifiable public source. The most-cited:
- ·ANSI Z765 — the American National Standards Institute standard for measuring single-family residential square footage. Drives our distinction between gross, livable, and below-grade area.
- ·BOMA Z65.1 — Building Owners and Managers Association standard for commercial floor measurement. Referenced where commercial concepts (gross, rentable, usable) come up.
- ·Manufacturer coverage specs — paint gallons (Sherwin-Williams, Benjamin Moore typical 350 sq ft per coat), shingle bundles (3 per square = 100 sq ft), drywall sheets (4×8 = 32 sq ft, 4×12 = 48 sq ft), tile box coverage. Always cross-checked against current product datasheets.
- ·Industry-standard waste factors — 5–10% straight flooring, 10–15% diagonal tile, 20% herringbone/chevron, 10% drywall, 10–15% roofing — drawn from contractor and trade-association consensus, not invented.
- ·Geometric formulas — π × r² for circles, (b × h) ÷ 2 for triangles, Heron's formula for triangles given three sides, ((a + b) ÷ 2) × h for trapezoids. Standard math, no proprietary anything.
How we keep results accurate
Calculator math is open. All formulas are implemented in plain TypeScript in our public source. There are no "adjustments," weighting factors, or hidden multipliers. Length × width is length × width.
Coverage rates are reviewed annually. Material coverage rates can drift as product formulas change (especially paint and roofing). We review and update the values on the calculators every January and every July.
Reader corrections are welcomed. If you spot an error in a formula, a coverage rate, or a measurement claim, email us. Verified corrections are applied within a week, and we credit the source where we can.
What this calculator is — and isn't — for
- · Material orders (flooring, paint, tile, sod)
- · Project budgeting and cost estimates
- · DIY planning
- · Comparing real estate listings
- · Quick sanity checks on contractor quotes
- · Splitting rent by room area
- · Real estate appraisals (hire a licensed appraiser)
- · Building permit applications (get a surveyor)
- · Insurance claims (use insurer-approved measurement)
- · HVAC sizing (Manual J load calc, not just sq ft)
- · Solar production estimates (site-specific assessment)
- · Structural or load-bearing decisions
Privacy & data
The calculator runs entirely in your browser. We don't store the dimensions you enter, we don't require an account, and we don't sell or share data with advertisers. The only things tracked are anonymous, aggregate page-view counts so we know which calculators get used.
Full details: privacy policy.
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