Paint Calculator
Estimate paint gallons or liters needed for room walls and ceilings. Subtracts doors and windows. Number of coats + primer option included. Imperial and metric.
Paint Calculator
How to use the Paint Calculator
Measure the room
You need three numbers for a rectangular room: length, width, and wall height. Measure tip-to-tip along baseboards for length and width; measure floor-to-ceiling for height. For L-shaped rooms, split into two rectangles and add the wall areas (or run the calculator twice). Standard residential ceiling heights: 8 ft (2.4 m) in older US homes, 9 ft (2.7 m) in newer construction, 2.4–2.6 m for typical ASEAN apartments.
Count doors and windows
Each door is approximated as 21 ft² / 1.8 m² (standard 7×3 ft / 2×0.9 m door). Each window is approximated as 15 ft² / 1.5 m² (standard 5×3 ft / 1.5×1 m window). The calculator subtracts these from wall area. For non-standard openings (sliding glass doors, picture windows, archways), adjust the count to approximate the area being subtracted — e.g. a 6×7 ft sliding door = ~2 standard "doors" in subtraction terms.
Pick surface type and coats
Smooth walls (modern drywall, well-sealed) cover at ~350 ft²/gal (~8.6 m²/L) — the industry standard for premium latex paints. Textured walls (popcorn ceilings, knockdown, orange peel finishes, brick, masonry) drop coverage to ~275 ft²/gal (~6.7 m²/L) because the texture eats more paint per visible square foot. Coats: two is standard for any color change; three for white-over-dark or premium results; one is only safe for color-on-color top-up.
Add primer for color or surface changes
Check "Add primer estimate" when going from dark-to-light, painting over stains, painting fresh drywall, or covering glossy surfaces. Primer coverage is ~300 ft²/gal (~7.4 m²/L) and only one coat is typically needed. If you're recoating with similar color over already-painted walls in good condition, skip primer — modern self-priming paints handle that case in 2 coats. Round UP to whole cans; partial cans get sticky and unusable within months.
Paint math — coverage rates, coats, and the cost of running short
Paint coverage is one of the most over-confidently-claimed numbers in home improvement. "One gallon covers 350 ft²" is true under specific conditions: smooth surface, single coat, experienced applicator, premium paint, no waste. In practice, the gap between rated coverage and real coverage is usually 15–25%. Textured walls eat paint. Roller fuzz absorbs paint. Spillage during pour, partial-can dry-out, and overspray with sprayers all leak gallons that never make it to the wall. The 10% waste buffer baked into this tool's default isn't pessimism — it's calibration to real-world performance, the same way the concrete calculator's 10% waste buffer is.
Why two coats is non-negotiable for color changes
Even premium "one-coat" paints generally need two coats for any meaningful color change. Why: the second coat isn't just adding more color — it's filling micro-pinholes left by the first coat, evening out brush / roller stippling, and depositing enough pigment to fully obscure the substrate. Modern self-priming paints (Behr Marquee, Sherwin-Williams Emerald, Dulux Diamond) shorten the timeline by combining primer + paint chemistry, but they don't eliminate the need for two coats over color changes. Three coats is the right call for white-over-dark, painting over stains, or any premium project. One coat only works for color-on-color top-ups where you're refreshing existing paint.
Running short on paint isn't just inconvenient — every retail color is mixed from a base + tints to match a recipe. Two gallons mixed three months apart will subtly differ. Buy ALL paint for one job in one purchase, or accept a visible band on the wall.
The 5-gallon pail crossover
Most major retailers (Home Depot, Lowe's, Sherwin-Williams stores, Dulux trade counters across ASEAN) price 5-gallon pails at roughly 4× the price of a 1-gallon can — meaning the per-gallon price drops by ~20% at the 5-gallon size. The crossover is sharp: at 4 gallons you should buy four 1-gal cans; at 5 gallons you should buy one 5-gallon pail. Above 5 gallons (large rooms, whole-house projects, exterior siding work), 5-gal pails are the only sensible option. A 5-gallon pail is also more colorimetrically consistent than five separately-mixed 1-gallon cans — important when you're painting a big surface where batch variation would be visible.
The ASEAN paint-market angle
Paint distribution and pricing varies more across ASEAN than most Western homeowners expect. Singapore is dominated by Nippon Paint (Japanese-owned, market leader), Dulux (AkzoNobel), and Jotun — all three sell in 1L, 5L, and 18L containers (the metric equivalents of US quart / gallon / 5-gallon). Coverage rates on cans are quoted in m²/L, typically 10–14 m²/L for premium paints on smooth surfaces (slightly higher than US ratings because the testing standard differs). Malaysia / Indonesia are heavy Nippon Paint / Jotun markets with ICI Dulux trailing; rural markets have local brands (TOA, JBP, Beger across Thailand) at lower price points. Vietnam / Philippines / Thailand see strong competition from regional brands undercutting global majors by 20–40%. Across the region, "premium" paint typically means the major-brand top tier (Nippon Hydroplus / Aqua, Dulux Weathershield, Jotun Royal) — equivalent to Behr Marquee or Sherwin-Williams Emerald in the US. For budget projects, the major-brand mid-tier lines (Nippon Vinilex, Dulux Pentalite) are perfectly serviceable; avoid the lowest-tier "economy" lines for any visible surface — coverage rates drop to 8–10 m²/L and you'll need 3 coats instead of 2.
10 Things to Know About Paint Coverage
"350 ft² per gallon" is the industry-standard coverage claim — but it assumes smooth surfaces, experienced applicators, and zero waste. Real-world coverage is typically 280–320 ft²/gallon for premium paints.
Textured surfaces (popcorn ceilings, knockdown, orange peel, brick) cut coverage by 20–30% because the texture creates more actual surface area per visible square foot.
The "one-coat" claim on premium paints is technically true for color-on-color refreshes only. Any meaningful color change needs two coats — even with self-priming formulas.
A standard interior door is ~21 ft² (1.8 m²) on each side; a standard window is ~15 ft² (1.5 m²). Sliding glass doors and picture windows can be 3–5× larger — account for them.
5-gallon pails cost roughly 4× the price of 1-gallon cans — meaning per-gallon savings of ~20%. The crossover happens at the 5-gallon mark; below that, buy individual cans.
Custom-tinted paints are mixed from a base + colorants per a digital recipe. Re-tinting the same recipe weeks later can drift by 0.5–2% in color value — invisible on small samples, but visible as a band on a finished wall.
The oldest known paint dates to ~40,000 years ago — red ochre handprints in the Cueva de Maltravieso cave in Spain. The pigments survive because iron oxide is chemically stable for tens of thousands of years.
Modern latex (water-based) paint dries by water evaporation, not chemical curing — the surface is "dry to touch" in 1–2 hours but isn't fully cured for 14–30 days. Avoid hard scrubbing, leaning furniture, or hanging art for the first two weeks.
The most expensive paint pigment in history is "Yves Klein Blue" (IKB) — a synthetic ultramarine patented by French artist Yves Klein in 1960. Authentic IKB paint costs over $1,000/liter today.
Major brands' top-tier lines (Behr Marquee, Sherwin-Williams Emerald, Benjamin Moore Aura, Nippon Hydroplus, Dulux Weathershield) all use self-crosslinking acrylic resins — making them more washable and scuff-resistant than budget paints.
Frequently Asked Questions
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Rated coverage assumes ideal conditions: smooth surface, experienced applicator, single coat, premium paint, zero waste. Real-world losses come from texture (cuts coverage 20–30%), roller absorption (a new roller eats a half-pint), tray spillage, paint left in the brush / roller at the end, drips, and the puddle in the bottom of the can you can't get out. The 10% waste buffer baked into this calculator accounts for these losses. The "ft² per gallon" number on the can is a best-case benchmark, not a realistic estimate.
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For any color change: yes. Even premium "one-coat" paints generally need two coats to fully obscure the underlying color, fill micro-pinholes from the first coat, and even out brush / roller stippling. One coat is only safe for color-on-color refresh — repainting a white wall white, or a beige wall beige. Three coats is the right call for white-over-dark, painting over stains or smoke damage, or any premium project where you want a flawless finish. Always plan for 2; budget for 3 if you're not sure.
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Always: fresh drywall (it's porous and uneven), stained surfaces (water marks, smoke, marker bleed-through), glossy surfaces (paint won't adhere to glass-like finishes), going dark-to-light (without primer you'll need 3–4 coats of finish paint). Skip primer when: recoating already-painted walls in good condition, color-on-color refresh, using modern self-priming premium paints (Behr Marquee, Sherwin-Williams Emerald, Nippon Hydroplus) on intact existing paint. Primer coverage is ~300 ft²/gal (~7.4 m²/L) and one coat is typically enough.
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The crossover is at 5 gallons. Below that, buy 1-gallon cans. At or above 5 gallons, buy a 5-gallon pail — it's priced at roughly 4× a 1-gallon can (~20% per-gallon savings) and is more colorimetrically consistent than five separately-mixed 1-gal cans. Above 5 gallons (large rooms, exterior siding, whole-house), use 5-gal pails exclusively. For touch-ups, save a small jar of original paint from the same batch — even a quart of the same batch is more reliable than re-tinting later.
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Split the room into rectangles. For an L-shape, run the calculator twice — once for each rectangle — and sum the gallons. For odd geometries with bay windows or alcoves, treat each alcove as its own mini-room. For ceilings with tray / coffer / barrel features, the rated "ceiling area" undercounts — add 15–25% to ceiling gallons for any 3D detail. For triangular gable walls, the height × width calculation overcounts — multiply the result by 0.5 since you're painting a triangle, not a rectangle.
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Only if you're painting the ceiling the same color as the walls. Most projects use a different color (typically flat white) for the ceiling vs an eggshell or satin on the walls — these are different paint products, not just different colors. Uncheck "Include ceiling" if you're calculating walls only and run the calc again with just the ceiling area (length × width) for the ceiling paint estimate. Flat ceiling paint costs ~30% less than wall paint and covers slightly less area per gallon (~300 ft²/gal).
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This calculator handles walls + ceiling only. Trim, baseboards, doors, and window frames are typically painted in a different finish (semi-gloss or gloss) for durability and contrast. Rule of thumb: a standard room needs about 1 quart of trim paint per door + windows + baseboards combined — a 12×15 room with 1 door + 2 windows + baseboards takes ~1 quart of semi-gloss trim. For just doors: ~1 quart covers 4–6 doors depending on style and primer needs. Plan trim paint separately from wall paint.
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Premium paint (Behr Marquee, Sherwin-Williams Emerald, Benjamin Moore Aura, Nippon Hydroplus, Dulux Weathershield) costs 2–3× budget paint and is worth it for: 30% higher coverage per coat (less paint needed), self-crosslinking acrylic resins (much more washable), better hide (often achieving full coverage in 2 coats vs 3), longer-lasting color stability (less fading over 5–10 years). Budget paints work fine for low-traffic spare bedrooms, closets, or rental flips — but for primary living spaces, premium paint saves money over the project lifetime by reducing repaint frequency and labour.
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No. All calculations run entirely in your browser via JavaScript. There's no server roundtrip — open DevTools → Network and confirm zero outbound requests as you change inputs. Room measurements stay on your device. Safe for confidential commercial estimates, multi-property dev calculations, or any room data that shouldn't leave your machine. Close the tab and nothing remains.
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Yes, with three adjustments: (1) Set surface to "Textured" — exterior siding (wood lap, vinyl, brick, stucco) is always textured and absorbs more paint than interior smooth walls. (2) Bump waste buffer to 15–20% for exterior work — wind, overspray, and weather make exterior pours messier. (3) Use exterior-grade paint (Behr Marquee Exterior, SW Duration, Nippon Weatherbond, Dulux Weathershield) — interior paint will not survive outdoor UV / rain cycling. The math is identical; just enter wall dimensions as if measuring exterior siding length × wall height.
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