Paint Calculator
How Much Paint Do You Actually Need?
Most people either buy too much paint (wasting money) or not enough (making an extra trip mid-project when the store no longer has the exact mixed color). Getting the calculation right upfront is a 2-minute task that saves frustration and money. This calculator accounts for room dimensions, doors, windows, number of coats, and ceiling — everything you need for a complete paint order.
How to Use This Calculator
Enter your room length, width, and ceiling height, then specify the number of doors and windows to subtract. Choose your number of coats, enter your paint's coverage rate (from the can label — typically 350–400 sq ft/gallon), and indicate whether you're painting the ceiling. Hit Calculate Paint to see total gallons for walls and ceiling separately.
How the Area Is Calculated
Ceiling area is simply length × width. Ceiling paint is typically the same coverage rate as wall paint but is usually purchased separately (ceiling paint has a flat finish that minimizes glare).
Real-World Example
Using the defaults — 15 ft × 12 ft room, 9 ft ceiling, 1 door, 2 windows, 2 coats, 350 sq ft/gal coverage, ceiling included:
- Gross wall area: (15+12) × 2 × 9 = 486 sq ft
- Subtract doors/windows: 21 + 30 = 51 sq ft
- Net wall area: 435 sq ft
- Wall paint (2 coats): 435 × 2 ÷ 350 = 2.49 gal → 3 gallons
- Ceiling area: 15 × 12 = 180 sq ft
- Ceiling paint (2 coats): 180 × 2 ÷ 350 = 1.03 gal → 2 gallons
- Total: ~5 gallons
Note: ceilings are often done in just 1 coat (especially if painting the same white), which would drop ceiling paint to 1 gallon and save money.
How Many Coats Do You Need?
- 1 coat — suitable only when painting the same or very similar color with a high-quality paint. Rarely ideal; coverage is usually patchy.
- 2 coats — standard for most projects. Provides even coverage, full color depth, and durability. Factor this into your order.
- Primer + 2 coats — required when making dramatic color changes (dark to light or light to very dark), painting new drywall, covering stains or repairs, or painting over a glossy surface. Primer is calculated separately and typically covers 300–400 sq ft/gal.
- 3 coats — sometimes needed for very saturated deep colors (navy, red, black) that are difficult to achieve in 2 coats even with quality paint.
Paint Buying Tips
- Always round up — buy one more gallon than the calculator says. Leftover paint seals well and is invaluable for touch-ups years later when you can't match the exact color.
- Premium paint covers better — better paints have higher pigment density and often cover 400 sq ft/gal vs. 300 sq ft/gal for budget paints. The cost difference often pays for itself in fewer gallons needed and fewer coats required.
- Buy ceiling and wall paint separately — ceiling paint has a flat (matte) finish designed to minimize light reflection. Wall paint comes in various sheens (flat, eggshell, satin, semi-gloss) depending on the room and desired durability.
- Test before committing — buy a sample pot and apply a 12×12 inch patch to your wall. Colors look dramatically different on a wall under room lighting versus on a paint chip card in the store.
- Match the sheen to the room — flat/matte for low-traffic areas, eggshell or satin for living areas and bedrooms, semi-gloss or gloss for kitchens, bathrooms, and trim (easier to clean).
Frequently Asked Questions
How accurate is the 350 sq ft/gal default coverage rate?
It's a reasonable average. Budget and mid-range paints typically cover 300–350 sq ft/gal; premium paints can reach 400 sq ft/gal. The coverage rate is always listed on the paint can label — use that number for the most accurate calculation. The rate assumes normal application with a roller on a smooth, primed surface; textured walls, rough drywall, or very porous surfaces will reduce coverage.
Do I need to prime before painting?
Not always. You need primer when: painting new drywall (it absorbs paint aggressively), covering a stain (water damage, smoke, crayon), making a dramatic color change, painting over gloss paint, or repairing patches. If you're painting over a similar color with a quality paint-and-primer product, you can often skip a separate primer coat. When in doubt, prime — it saves paint and produces a better finish.
Should I include closets in my calculation?
Only if you're painting them. Many people paint closet interiors white regardless of the room color — calculate them separately using the closet dimensions. Closets add meaningful square footage (especially walk-ins) and are easy to forget when estimating paint.
What's the best order for painting a room?
Ceiling first, then walls, then trim and doors last. This way, any drips or splatters from the ceiling get covered when you paint walls, and any paint that gets on the trim from doing walls gets covered when you do trim. Use painter's tape on trim before doing walls if your cut-in skills aren't sharp.
How do I store leftover paint?
Seal the lid tightly (tap firmly with a rubber mallet, not a hammer), store at room temperature away from freezing, and keep it upside down for a minute to create an airtight seal before turning right-side up. Properly stored latex paint lasts 10+ years. Write the room name and color on the lid. Never store paint in a garage where it can freeze — freezing permanently ruins latex paint.