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Paint · US units

Paint Calculator — Gallons and Cost

Coverage is per coat. Default 350 sq ft/gal is the PaintCare fallback when the can is silent — backed by Sherwin-Williams Emerald/SuperPaint and Benjamin Moore Ultra Spec at 350–400. PPG SPEEDHIDE is ~400, not 350. Do not treat 350 as an EPA number.

Basket 2026-08-27

Room and coats

ft
ft
ft
coats

Behr system rec is 2 coats. How-to copy often describes one coat of coverage.

20 sq ft each (Behr how-to).

15 sq ft each (Behr how-to).

sq ft/gal

Default 350 is the PaintCare fallback when the can is silent. SW Emerald/SuperPaint and BM Ultra Spec list 350–400. PPG SPEEDHIDE is ~400, not 350. Behr lists 250–400. Not an EPA figure.

Waste factor

10% is a calculator convention, not a manufacturer TDS. Sherwin-Williams only says keep a little extra.

$

Index 2026-08-27. Home Depot online, zip not pinned.

$

Buy this month

3 gal

2.194 gal exact · 349 sq ft net · 2 coats

$98.94

Gross walls
384 sq ft
Doors + windows
−35 sq ft
Film (area × coats)
698 sq ft
After 10% convention
767.8 sq ft

350 sq ft/gal is per coat. Two coats is twice the film, not a different coverage number.

What calculator.net does not show

Geometry sites stop at area ÷ 350. This tool keeps the manufacturer split honest: 350 is a one-coat spread rate, Behr how-to openings are 20 sq ft per door and 15 sq ft per window, two coats is the system recommendation even when marketing copy talks about one-coat hide, and 10% extra is a calculator convention. Sherwin-Williams’ FAQ only says keep a little extra — it does not publish 10%.

Worked US example: 12×12 bedroom

8 ft walls, 1 average window, 1 average door, two coats, 350 sq ft/gal, ceiling off.

Gross walls = 2 × (12 + 12) × 8 = 384 sq ft
Openings    = 20 + 15 = 35 sq ft   (Behr how-to)
Net         = 384 − 35 = 349 sq ft
Film        = 349 × 2 coats = 698 sq ft
Exact gal   = 698 ÷ 350 = 1.994 gal
Buy         = 2 gal  (round up, 0% waste)
With 10%    = 1.994 × 1.10 = 2.194 gal → buy 3 gal
Cost @ $32.98 Behr Premium Plus eggshell 205001
            = 2 × $32.98 = $65.96   or   3 × $32.98 = $98.94

Behr exterior how-to still lists 250–400 sq ft per gallon for one coat. If you are painting new drywall or jumping from dark to light, keep two coats and consider the 15% toggle or drop coverage toward 250 rather than inventing a third “fudge factor.”

Optional primer uses Behr 43601 at $29.98/gal from the same day’s basket. Primer gallons are a separate line — we do not silently double the finish coat.

Citations

  1. PaintCare. Buy the Right Amount of Paint to Reduce Waste. Accessed 2026-08-27. https://www.paintcare.org/buy-right/ — If the can does not list coverage, PaintCare says use 350 sq ft per gallon as a rough estimate. Coverage on cans is typically 300–400 sq ft/gal. This is the site default fallback — not an EPA figure.
  2. Sherwin-Williams. Emerald Interior Acrylic Latex product data sheet. Accessed 2026-08-27. https://www.sherwin-williams.com/document/PDS/en/035777628072/ — Coverage: 350–400 sq. ft. per gallon @ 4 mils wet, 1.5 mils dry. One coat at that film thickness.
  3. Sherwin-Williams. SuperPaint Interior Latex Satin product data sheet. Accessed 2026-08-27. https://www.sherwin-williams.com/document/PDS/en/035777315682/ — Coverage: 350–400 sq. ft. per gallon @ 4 mils wet, 1.5 mils dry.
  4. Sherwin-Williams. How to Use Paint Calculator | FAQs. Accessed 2026-08-27. https://www.sherwin-williams.com/en-us/color/color-tools/paint-calculator — A gallon typically covers about 350–400 sq ft. SW says depending on texture and desired coverage, keeping a little more than a gallon on hand may be best. That is not a numeric waste percentage.
  5. Benjamin Moore. Ultra Spec interior latex coverage (350–400 sq ft/gal). Accessed 2026-08-27. https://www.benjaminmoore.com/en-us/specifications-and-data/ultra-spec — Ultra Spec architectural coatings list 350–400 sq ft per gallon on product data. Same one-coat spread-rate band as SW Emerald/SuperPaint.
  6. PPG. SPEEDHIDE interior latex spreading rate. Accessed 2026-08-27. https://www.ppgpaints.com/products/speedhide-interior-latex — SPEEDHIDE interior latex is specified around 400 sq ft/gal, not 350. Do not mix this rate into the PaintCare 350 fallback.
  7. Behr. How Much Interior Paint to Buy for your Home. Accessed 2026-08-27. https://www.behr.com/consumer/how-to/interior/determine-how-much-interior-paint-to-buy — Average window about 15 sq ft; average door about 20 sq ft. How-to copy discusses one coat coverage; Behr system recommendation is two coats for most color changes and new work.
  8. Behr. How Much Paint Do I Need? (exterior). Accessed 2026-08-27. https://www.behr.com/how-to/exterior/how-much-exterior-paint-to-buy — One gallon of any BEHR paint covers 250–400 sq ft in one coat. Same 15 / 20 sq ft opening allowances. Factor a second coat if necessary.

These calculators estimate material takeoff for planning. They are not engineering, structural, or code advice. Confirm spans, mixes, fastener schedules, and permits with a licensed professional and the manufacturer’s current data sheet. Local shelf prices and tax are not this index.