Stop guessing at the paint aisle — get a gallon count before you buy.
Before you startGrab a tape measure and note your dimensions. This calculator works in feet and inches — measure the actual area, not the room label.
What's next?Got your gallon count? <a href="/interior-painting-cost/">See interior painting costs</a> for DIY vs pro pricing, <a href="/compare/paint-vs-wallpaper/">compare paint vs wallpaper</a>, or <a href="/drywall-calculator/">estimate drywall sheets</a> if starting from studs.
How to estimate paint for a room
Paint is sold by the gallon, but you buy coverage for wall area × coats. Skipping the math leads to mid-project store runs or leftover gallons you cannot return once tinted.
- Find wall area: perimeter × ceiling height.
- Subtract doors (~20 sq ft each) and windows (~15 sq ft each).
- Add ceiling (length × width) if you are painting it too.
- Multiply by number of coats.
- Divide by coverage per gallon on the paint can.
This calculator uses industry-average deductions — measure your openings if you want precision.
Worked example: 14×12 ft room, 8 ft ceilings
- Perimeter: 2 × (14 + 12) = 52 ft
- Wall area: 52 × 8 = 416 sq ft
- Minus 2 doors (40) and 2 windows (30): 346 sq ft paintable
- Two coats: 692 sq ft total coverage needed
- At 350 sq ft/gal: 692 ÷ 350 = 1.98 → buy 2 gallons (walls only, no ceiling)
Toggle Include ceiling in the calculator if you are painting the fifth wall — that adds length × width to the total.
Coverage guidelines
| Surface |
Typical coverage |
| Smooth previously painted wall |
350–400 sq ft/gal |
| Textured or porous drywall |
250–350 sq ft/gal |
| Dramatic color change |
Plan 2 coats minimum |
| Dark over light (or reverse) |
2 coats + primer |
Always read the can. Premium paints and flat finishes spread differently than builder-grade eggshell.
Primer is not included here
New drywall, stains, or dark-to-light jumps often need primer first — buy primer separately; this estimate is for finish coats only.
Common primer scenarios:
- New drywall — one coat primer before color
- Stains / smoke / water marks — stain-blocking primer
- Bold color changes — tinted primer reduces topcoat count
Primer coverage is often 200–300 sq ft/gal — do not assume it matches finish paint.
Trim, doors, and cabinets
This tool estimates main wall fields. Trim, doors, and cabinets are usually calculated separately:
- Trim: measure linear feet × height of base + casing; often 1–2 quarts per average room
- Doors: one door face ≈ 20 sq ft both sides if painting slab doors
- Ceilings: enable the ceiling toggle or add length × width manually
Buying strategy
- Custom tints: buy an extra quart for touch-ups — batch drift is real
- One-gallon vs five-gallon: five-gallon pails save money on whole-house jobs if color is locked
- Spray vs roll: sprayers use more paint through overspray — add 10% if spraying
Drywall project next?
If you are finishing new walls before paint, estimate sheets with our drywall calculator — hang, tape, and prime before you buy finish color.
Paint or wallpaper?
For accent walls and pattern, compare paint vs wallpaper — then use this calculator if paint wins.
Frequently asked questions
How much paint do I need for a 12x12 room?
A 12×12 ft room with 8 ft ceilings has about 384 sq ft of wall area before doors and windows. With two coats and 350 sq ft/gallon coverage, you typically need about 2–3 gallons for walls only.
How many square feet does a gallon of paint cover?
Most interior wall paints cover 350–400 square feet per gallon on smooth, primed surfaces. Textured walls and porous surfaces cover less — check the label.
Do I need two coats of paint?
Two coats are standard for even color and durability, especially when changing colors or covering darker shades. Same-color refreshes may look fine with one coat.
Should I buy extra paint?
Buy one extra quart for touch-ups, especially if you custom-tinted the color — matching later batches can be difficult.
Do I need primer before painting?
Yes in most cases. Primer seals porous surfaces, blocks stains, and helps paint adhere evenly. Always prime over new drywall, patched areas, or when going from dark to light colors. Paint-and-primer-in-one products work for same-color refreshes on clean surfaces but are not a substitute for dedicated primer on bare drywall.
What is the difference between flat, eggshell, and semi-gloss paint?
Flat (matte) hides wall imperfections best but is harder to clean — good for ceilings and low-traffic rooms. Eggshell has a slight sheen and is wipeable — the most common choice for living areas and bedrooms. Semi-gloss is durable and moisture-resistant — best for trim, doors, kitchens, and bathrooms.
How do I calculate paint for a ceiling?
Measure the floor area of the room (length × width) — the ceiling area is the same. Divide by paint coverage per gallon. One gallon typically covers 350–400 sq ft of smooth ceiling. Use flat ceiling paint (not wall paint) to minimize roller stipple and glare.
Does paint color affect how many coats I need?
Yes. Going from dark to light often needs 3 coats (or a tinted primer plus 2 coats). Same-color refreshes may need only 1 coat. Deep base colors (reds, yellows, dark blues) are inherently more translucent and often require 3+ coats for full coverage.