Paint Calculator
Use this free paint calculator to find out exactly how many gallons of paint you need for any room. Enter your room length, width, and ceiling height, select the number of coats, and the calculator instantly tells you how many gallons to buy — with door and window deductions already accounted for.
Based on 400 sq ft coverage per gallon (industry standard) · Each door/window deducts 20 sq ft · Always round up to the nearest full gallon · Calculator covers walls only — add ceiling (1 gal/400 sq ft) and trim (1 qt/room) separately
Estimates based on 2026 US average pricing from Sherwin-Williams, Benjamin Moore, and Behr product data. Coverage varies by paint brand, surface texture, and application method.
Understanding the Calculator Inputs
This calculator estimates wall paint quantity for a single rectangular room. It applies the industry-standard 400 sq ft coverage per gallon — the rate used by Sherwin-Williams, Benjamin Moore, Behr, and PPG in their product specifications for smooth, previously painted surfaces. It deducts unpaintable area for doors and windows, then multiplies by your chosen number of coats.
Room Dimensions
Measure the interior floor dimensions — length and width from wall to wall. For L-shaped rooms, calculate each rectangular section separately and add the wall areas. Ceiling height is measured from finished floor to finished ceiling — standard residential ceilings are 8, 9, or 10 feet. For vaulted or cathedral ceilings, use the average height at midpoint.
Doors and Windows
The calculator deducts 20 sq ft per door or window — a standard allowance covering a typical 32"×80" door or a 36"×48" double-hung window. Count each door and window separately. For very large picture windows or sliding glass doors, count them as 2 openings each.
Number of Coats
2 coats is standard for virtually all paint jobs and is what paint manufacturers assume in their coverage specifications. Use 1 coat only when repainting the exact same color with premium paint over a clean surface in good condition. Use 3 coats when covering dark colors with a significantly lighter shade, painting over stains, or applying paint without primer on new drywall.
What This Calculator Does NOT Include
- Ceiling paint — add 1 gallon per 400 sq ft of ceiling area separately
- Trim paint — add 1 quart per room for baseboards, door frames, and window casings
- Primer — add 1 gallon per 400 sq ft if priming is needed (new drywall, stain coverage, major color change)
- Labor — see the cost section below for professional painting rates
After your project is done, buy one extra quart from the same batch and store it with the paint can. Touch-ups are inevitable — scuffs, nail holes, small dings. Having the exact same batch color saves you from trying to match at the store later, which almost never produces a perfect match.
3 Real-World Paint Examples
Complete paint lists for three common painting projects — walls, ceiling, and trim calculated separately so you know exactly what to bring to the paint counter.
Example 1 — Standard Bedroom (12×12 ft, 9 ft ceiling, 2 coats)
A typical bedroom repaint — mid-range paint, same-color ceiling, white trim refresh. 2 doors/windows.
| Surface | Area | Gallons | Paint Type | Cost (mid-range) |
|---|---|---|---|---|
| Walls (2 coats) | 352 sq ft paintable | 2 gallons | Mid-range interior eggshell | $70–$110 |
| Ceiling (1 coat) | 144 sq ft | 1 gallon | Flat ceiling white | $25–$40 |
| Trim (1 coat) | ~80 LF baseboards + doors | 1 quart | Semi-gloss white | $12–$20 |
| Total all surfaces | $107–$170 | |||
Real-world note: A 12×12 bedroom is a half-day DIY project for an experienced painter — about 3–4 hours including cutting in edges and rolling. The single biggest time-saver: proper prep (taping, patching, sanding) before touching a brush. Rushing prep is what produces amateur-looking results. Paint in order: ceiling first, walls second, trim last.
Example 2 — Open-Plan Living/Dining Room (20×24 ft, 9 ft ceiling, 2 coats)
A large open-plan main area — accent wall in a dark color, remaining 3 walls lighter, 5 windows/doors, premium paint.
| Surface | Area | Gallons | Paint Type | Cost (premium) |
|---|---|---|---|---|
| 3 main walls (2 coats, light) | ~500 sq ft paintable | 2 gallons | Premium eggshell | $110–$160 |
| Accent wall (3 coats, dark) | ~196 sq ft | 2 gallons | Premium eggshell (dark) | $110–$160 |
| Ceiling (1 coat) | 480 sq ft | 2 gallons | Flat ceiling white | $50–$80 |
| Trim (1 coat) | ~150 LF | 1 quart + 1 pint | Semi-gloss white | $20–$35 |
| Total all surfaces | $290–$435 | |||
Real-world note: Dark accent walls require 3 coats over a light base — plan for it upfront. A deep navy, charcoal, or forest green going over white needs a grey primer coat first, then 2 coats of the dark color. Skipping primer and trying to cover white with 2 coats of dark paint produces a patchy result and costs you an extra trip to the store anyway.
Example 3 — Full House Interior (1,800 sq ft home, 5 rooms + hallways)
A complete interior repaint for a house sale or full renovation. Contractor-painted, mid-range paint throughout, all surfaces.
| Area | Paint Qty | Unit Cost | Total Materials |
|---|---|---|---|
| Walls — all rooms (2 coats) | ~10 gallons | $35–$55/gal | $350–$550 |
| Ceilings (1 coat) | ~5 gallons ceiling white | $25–$35/gal | $125–$175 |
| Trim — all rooms (1 coat) | ~3 gallons semi-gloss | $35–$55/gal | $105–$165 |
| Primer (new patches) | 1 gallon | $25–$40/gal | $25–$40 |
| Total paint materials | $605–$930 | ||
| Professional labor (whole house) | $3,000–$7,000 | ||
| All-in contractor cost | $3,605–$7,930 | ||
Real-world note: Professional painters charge $2–$6 per sq ft of paintable wall area for labor (HomeAdvisor 2026 data) — an 1,800 sq ft home with roughly 1,200 sq ft of paintable wall area runs $2,400–$7,200 in labor alone. For a house-sale repaint where speed matters, a professional crew completes this in 2–3 days vs 2–3 weekends DIY. Use our bathroom remodel calculator for full room renovation estimates.
Paint Coverage Chart by Room Size
Quick reference for common room sizes at 9 ft ceiling height, 2 doors/windows, 400 sq ft coverage per gallon. Walls only — add separately for ceiling and trim.
| Room Size | Wall Area | Paintable Area | 1 Coat | 2 Coats | 3 Coats |
|---|---|---|---|---|---|
| Small bedroom (10×10) | 360 sq ft | 320 sq ft | 1 gal | 2 gal | 3 gal |
| Standard bedroom (12×12) | 432 sq ft | 392 sq ft | 1 gal | 2 gal | 3 gal |
| Large bedroom (14×14) | 504 sq ft | 464 sq ft | 2 gal | 3 gal | 4 gal |
| Living room (16×20) | 648 sq ft | 608 sq ft | 2 gal | 4 gal | 5 gal |
| Large living room (20×24) | 792 sq ft | 752 sq ft | 2 gal | 4 gal | 6 gal |
| Open plan (24×30) | 972 sq ft | 932 sq ft | 3 gal | 5 gal | 8 gal |
Based on 9 ft ceilings, 2 doors/windows deducted, 400 sq ft/gallon per Sherwin-Williams, Behr, and Benjamin Moore product data. Textured walls reduce coverage by 10–15% — buy one extra gallon if your walls have texture.
Paint Cost by Type (2026)
Paint quality affects coverage, durability, washability, and how many coats you need. Spending more per gallon often means fewer gallons — premium paints with better hiding power frequently cover in one coat where budget paints need two.
| Paint Type | $/Gallon | Coverage | 12×12 Room (2 coats) | Best For |
|---|---|---|---|---|
| Standard / Budget | $25–$35 | 350–400 sq ft/gal | $50–$70 | Rentals, garages, low-traffic areas |
| Mid-Range | $35–$55 | 400 sq ft/gal | $70–$110 | Most bedrooms and living areas |
| Premium | $55–$80 | 400–450 sq ft/gal | $110–$160 | High-traffic areas, one-coat jobs |
| Exterior | $40–$70 | 300–400 sq ft/gal | $80–$140 | Siding, trim, outdoor surfaces |
| Primer (interior) | $20–$40 | 300–400 sq ft/gal | $40–$80 | New drywall, stains, color changes |
| Ceiling paint | $25–$45 | 400 sq ft/gal | $25–$45 per gal | All ceilings — flat finish hides imperfections |
Mid-range paints — Behr Premium Plus, Sherwin-Williams SuperPaint, Benjamin Moore Regal — offer the best combination of coverage, washability, and price for most residential rooms. Premium paints (Sherwin-Williams Emerald, Benjamin Moore Aura) are worth the extra cost in high-traffic hallways and kitchens where washability matters, or when you want to finish in one coat to save labor time.
Choosing the Right Paint Finish
Paint finish (sheen level) affects appearance, washability, and how forgiving the paint is of wall imperfections. The wrong finish for a room creates maintenance problems.
| Finish | Sheen Level | Best Rooms | Washability | Hides Imperfections? |
|---|---|---|---|---|
| Flat / Matte | None | Ceilings, low-traffic rooms | Poor | Yes — best for hiding flaws |
| Eggshell | Very Low | Bedrooms, living rooms | Good | Yes — popular choice |
| Satin | Medium-Low | Hallways, kids’ rooms, family rooms | Very Good | Moderate |
| Semi-Gloss | Medium-High | Kitchens, bathrooms, trim, doors | Excellent | Poor — shows every bump |
| Gloss | High | Trim, cabinets, furniture | Excellent | Poor — magnifies imperfections |
The Standard Approach for Most Homes
- Ceilings: Flat white ceiling paint — hides imperfections, zero glare
- Bedrooms and living rooms: Eggshell — cleanable with a damp cloth, soft appearance
- Kitchens and bathrooms: Satin or semi-gloss — stands up to moisture, grease, and frequent wiping
- Trim, baseboards, doors: Semi-gloss — durable, easy to clean, provides contrast to walls
- Hallways and high-traffic areas: Satin — better durability than eggshell where walls get touched constantly
Primer Guide — When You Need It and When You Don’t
Primer is a separate coat applied before paint to improve adhesion, block stains, and help paint bond properly. It’s not always needed — but skipping it when it is needed creates problems that no amount of extra paint coats will fix.
Always Use Primer When:
- Painting new drywall — bare drywall absorbs paint unevenly, producing a blotchy “flashing” effect. A PVA drywall primer seals the surface and is non-negotiable on new drywall.
- Covering water stains or smoke damage — regular paint doesn’t block stains; they bleed through every coat. Use a shellac-based or oil-based primer (Zinsser BIN, Kilz Original) specifically for stain blocking.
- Going from a very dark to a very light color — a dark navy or burgundy over white needs a grey tinted primer first, then 2 coats of the new color. Without primer, you’ll need 4+ coats for full coverage.
- Painting bare wood or metal — these surfaces need a bonding primer before paint or the paint will peel within months.
- Patched areas — spackle and joint compound are highly porous and absorb paint at a different rate, creating dull spots. Spot-prime any patched areas before painting.
Skip Primer When:
- Repainting the same or similar color over a clean, previously painted surface in good condition
- Using a high-quality paint-and-primer product for a minor color change
- Doing touch-ups on an existing painted surface
Even if you’re skipping a full primer coat, always spot-prime any patched holes or skim-coated areas with a small brush before rolling the final color. Unprimed patches absorb paint at a different rate and show up as dull circles through the finish coat — called “flashing.” A $10 pint of primer prevents this entirely.
Common Painting Mistakes
Calculating Only the Wall Area, Forgetting Ceiling and Trim
This calculator covers walls only. A complete room paint job requires ceiling paint (1 gallon per 400 sq ft of ceiling area), trim paint (1 quart per standard room), and possibly primer. Go to the paint counter with the full list — not just the wall gallon count — to avoid a second trip mid-project.
Buying Paint in the Wrong Sheen
The most common DIY paint mistake. Flat paint in a bathroom peels within a year from moisture. Gloss paint on living room walls shows every roller line and wall imperfection. Eggshell in a kitchen wipes out faster than satin. Match the finish to the room’s conditions — see the finish guide above.
Skipping Surface Prep
Fresh paint over dirty, glossy, or damaged walls looks bad immediately and fails faster. The correct prep sequence: wash walls with TSP or sugar soap, fill holes with spackle, sand smooth when dry, spot-prime patches, then paint. This adds 2–3 hours to a bedroom project and makes the difference between a professional-looking result and an amateur one.
Not Buying Enough of One Batch
Paint color can vary slightly between batches. If you run out mid-wall and buy another gallon from a different batch, the color difference is often visible in raking light. Always calculate your gallons, add one extra quart buffer, and buy everything in one trip. Check that all cans have the same batch number on the lid.
Applying the Second Coat Too Soon
The most common cause of peeling and lifting. Wait the manufacturer’s recommended recoat time — typically 2–4 hours for latex paint at 70°F with good ventilation. Cold temperatures, high humidity, or poor ventilation can extend this to 6+ hours. Touch the wall — if it feels tacky at all, wait longer.
How We Calculate
Gallons = CEILING(Paintable Area × Coats ÷ 400)
Wall area is calculated from room perimeter (2 × (L+W)) × ceiling height. Door and window deductions (20 sq ft each) are subtracted to get paintable area. The result is multiplied by number of coats and divided by 400 sq ft — the industry standard coverage rate used by all major paint manufacturers (Sherwin-Williams, Benjamin Moore, Behr, PPG) for smooth, previously painted surfaces with a single coat. We apply a ceiling function (always round up) because you can’t buy a fraction of a gallon.
Coverage decreases on textured surfaces (350 sq ft), porous or unpainted surfaces (300 sq ft), and very dark colors. The calculator uses 400 sq ft as a reliable conservative estimate for most residential repaint situations. Paint pricing reflects 2026 retail pricing at Home Depot, Lowe’s, and Sherwin-Williams stores.
Frequently Asked Questions
- Sherwin-Williams — Paint Product Data Sheets — Coverage rate specification (400 sq ft per gallon on smooth, previously painted surfaces, single coat) for SuperPaint, Emerald, and Duration product lines. Referenced for the 400 sq ft/gallon standard used in the formula and coverage chart. Sherwin-Williams, 2026 product documentation.
- Benjamin Moore — Paint Product Specifications — Coverage rate and recoat time specifications for Regal Select, Aura, and Natura product lines. Referenced for premium paint coverage rate (400–450 sq ft/gal) and recoat time guidance (2–4 hours at 70°F). Benjamin Moore & Co., 2026 product documentation.
- Behr — Premium Plus and Marquee Product Data — Coverage rate, sheen level performance, and washability specifications for interior latex paint lines. Referenced for the mid-range paint cost range and coverage data. Behr Process Corporation, 2026 product documentation.
- HomeAdvisor True Cost Guide 2026 — Professional interior painting labor cost data by room size and US region ($2–$6 per sq ft of paintable wall area). Referenced for the professional labor cost range in the full-house example and cost tables. HomeAdvisor / Angi, 2026.
- Zinsser / Rust-Oleum — Primer Product Specifications — Shellac-based primer (BIN) and water-based primer (Bulls Eye 1-2-3) stain-blocking performance, coverage rates, and application guidance for new drywall and stain coverage. Referenced for the primer guide section. Rust-Oleum / Zinsser, 2026 product documentation.
Paint pricing reflects 2026 US national average retail pricing from Home Depot, Lowe’s, and Sherwin-Williams stores. Coverage rates are manufacturer specifications for smooth, previously painted surfaces under normal conditions — actual coverage varies by surface texture, porosity, application method, and paint color. ConstructlyTools does not have a paid relationship with Sherwin-Williams, Benjamin Moore, Behr, or any paint manufacturer mentioned on this page.