How to use this calculator
- Measure room. Length and width in feet, plus ceiling height.
- Subtract openings. Count doors (≈ 21 ft² each) and windows (≈ 15 ft² each).
- Choose coats. Most jobs need 2 coats. Dark-over-light or stained surfaces may need 3.
- Read result. Round up to the nearest gallon — partial gallons stop being economical fast.
Formula
Gallons = ceil((wall area − doors − windows) × coats ÷ 350)
Worked example
A 12 × 14 ft room with 8 ft ceilings, 1 door and 2 windows needs 416 ft² of paintable area. Two coats = 832 ft² ÷ 350 = 3 gallons.
Common project sizes
Quick reference for the most common paint calculator use cases. Use these as a sanity check on your calculator inputs.
| Project | Dimensions | Result |
|---|---|---|
| Bathroom (8×6 ft, 8 ft ceil.) | 224 ft² wall | 1 gal · 0.5 gal primer |
| Bedroom (12×14 ft, 8 ft ceil.) | 416 ft² wall | 2 gal · 1 gal primer |
| Living room (16×20 ft, 9 ft ceil.) | 648 ft² wall | 3 gal · 1.5 gal primer |
| Whole 1,800 ft² home interior | ~3,000 ft² wall | 15 gal · 7 gal primer |
| Exterior siding (1,500 ft² home) | ~1,650 ft² siding | 14 gal body · 2 gal trim |
2026 cost reference
Typical retail price range in the United States for paint. Local pricing varies by region, supplier, and grade — confirm with two or three quotes before ordering.
Per gallon (interior premium)
$25 – $70
Builder-grade interior paint runs $20–$30/gal (Behr Marquee, Valspar 2000). Mid-tier is $30–$45/gal (Sherwin-Williams ProClassic, Benjamin Moore Regal). Designer / no-VOC / specialty finishes are $50–$70/gal (Farrow & Ball, Benjamin Moore Aura). For a typical 1,800 ft² home, expect $400–$1,000 in paint at mid-tier — buy by the 5-gal bucket for the best per-gallon price.
By the numbers — regional pricing
Snapshot of current US pricing for gallon (interior mid-tier latex, eggshell finish), broken down by Census region. Source: Big-box retail averages (Home Depot, Lowes, Sherwin-Williams contractor pricing); designer brands (Farrow & Ball, Aura) excluded.. Data as of April 2026; we refresh quarterly.
| Region | Low | High | Note |
|---|---|---|---|
| Northeast | $38 | $58 | — |
| Midwest | $32 | $52 | — |
| South | $33 | $54 | — |
| West | $36 | $60 | CARB-compliant zero-VOC formulas command $5–$10/gal premium in CA. |
How we calculate this
Assumptions baked in
Paintable area = (wall area) − (door area) − (window area), where the door default is 21 ft² (3' × 7') and window default is 15 ft² (3' × 5'). Coverage is 350 ft² per gallon on smooth, primed drywall — the figure published on most Sherwin-Williams, Behr, and Benjamin Moore spec sheets for one coat. Two coats is the default; the calculator multiplies area × coats then divides by 350.
Accuracy and margin of error
For smooth drywall over an existing painted surface in good condition, the 350 ft²/gal figure is accurate within ±10%. Coverage drops substantially on: bare drywall (down to 250 ft²/gal due to absorption), heavily textured surfaces (200–250 ft²/gal), and dark-to-light color changes (more coats needed). When in doubt, buy by the 5-gallon bucket — the price-per-gallon is 15–20% lower and an extra gallon for touch-ups in two years is always useful.
Edge cases this calculator does not handle
Cabinets and trim use significantly more paint per ft² because of the brushed application — buy quarts, not gallons, and expect ~150 ft²/quart coverage. Ceilings benefit from flat-finish paint (hides imperfections in raking light); walls usually get eggshell or satin. Bathrooms and kitchens need a mildew-resistant satin or semi-gloss.
Cited sources for this page
The figures and rules above are anchored to the following normative references. We link the underlying claim to its standard — not as generic SEO trust signals, but so you can audit any number on this page against a primary source.
Coverage of 350–400 ft² per US gallon at recommended dry film thickness is the spec-sheet figure on most major interior latex paints.
Source: Sherwin-Williams ProClassic Interior Acrylic Latex spec sheet
Low-VOC content limits (50 g/L for flats, 100 g/L for non-flats) are set by the EPA AIM rule and tightened further in California by CARB.
Source: US EPA Architectural Coatings Rule (40 CFR Part 59 Subpart D)
Tips for accurate results
- 1 US gallon covers ≈ 350 ft² in one coat on smooth drywall.
- Textured surfaces (popcorn, stucco) cover 250 ft²/gal — buy 30% more.
- Always buy paint in the same batch number to avoid color shifts.
- Save the empty cans — the label has the exact color formula for touch-ups.
Common mistakes to avoid
- Skipping primer over patched drywall — flash spots show through the topcoat in raking light. Spot-prime patches with stain-blocking primer.
- Buying one gallon for "just one coat" — coverage on the can is for ideal substrates. Realistic coverage on textured walls is 250–300 ft²/gal.
- Using flat sheen in bathrooms or kitchens — paint stains and is hard to clean. Use eggshell or satin in wet areas.
- Not boxing multiple gallons of the same color — even from the same batch, gallons vary. Pour all gallons into one 5-gal bucket and stir before starting.
When to consult a pro
Painting a single occupied room is solidly DIY — a quart of paint, a roller, a 2.5" angled brush, and a sash brush for cutting in around trim is all you need. Hire a painter for whole-house jobs (the prep alone takes a week), high or vaulted ceilings (scaffold or extension-ladder work), and any project with extensive cabinet refinishing. Pros also bid faster on multi-color schemes, where the cut-in time on every wall multiplies.