Paint guide
How Much Paint Do I Need?
Estimate gallons of paint from wall area, coats, coverage rate, openings, primer needs, and touch-up margin.
Updated Reviewed by SupplyCalc Editorial
Quick answer
Estimate paint by measuring wall area, subtracting large openings, multiplying by the number of coats, then dividing by the paint coverage rate. A common planning coverage is about 350 square feet per gallon, but the actual number depends on the paint, color change, surface texture, application method, and primer needs.
For a 12 ft by 10 ft room with 8 ft walls, the wall perimeter is 44 ft. Multiply by 8 ft height to get 352 square feet before openings. If doors and windows subtract 40 square feet, the paintable area is 312 square feet. Two coats need 624 square feet of coverage. At 350 square feet per gallon, that is 1.8 gallons, so plan on 2 gallons.
Paint estimate formula
Use this sequence for room walls:
- Wall area = room perimeter x wall height.
- Subtract doors, large windows, and untinted areas.
- Multiply by number of coats.
- Divide by coverage per gallon.
- Round up to the next practical container size.
Ceilings are separate. Multiply ceiling length by width, then divide by the ceiling paint coverage rate. Trim, doors, and cabinets also need separate estimates because they use different products and are often measured by linear feet or counted as pieces.
Paint coverage reference table
| Surface or condition | Planning coverage | Notes |
|---|---|---|
| Smooth primed wall | 350 to 400 sq ft per gallon | Most efficient common case |
| Textured wall | 250 to 350 sq ft per gallon | Texture holds more paint |
| Dark-to-light color change | 2 coats plus primer | Primer can reduce finish coats |
| New drywall | Primer plus paint | Joint compound and paper absorb differently |
| Accent wall | 1 to 2 coats | Depends on color and product |
| Ceiling | 300 to 400 sq ft per gallon | Estimate separately from walls |
Always use the product label for the final coverage value. Premium paints, deep bases, masonry coatings, and specialty finishes can vary.
Openings and coats
Subtract large doors and windows when they materially change the total. A standard interior door is often estimated around 20 square feet. A small window may not be worth subtracting if you want touch-up margin, but several large windows should be deducted.
Most wall repainting projects use two coats. One coat may work when the existing color is close, the surface is clean, and the paint is designed for high coverage. New drywall, stains, patched areas, glossy surfaces, and strong color changes need primer or extra finish coats.
Rounding and touch-up margin
Paint is usually bought in quarts, gallons, or five-gallon pails. Round up enough to finish the room and keep touch-up paint from the same batch. Running short can create sheen or color differences, especially if a second can is mixed later.
Do not over-subtract small openings. A modest remaining margin helps with roller loading, cutting in, spills, porous patches, and future touch-ups. If the estimate lands near the top of a gallon, buying the next size may be more practical.
Planning example
Consider a bedroom that is 11 ft by 13 ft with 8 ft walls. The room perimeter is 48 ft, so wall area is 384 square feet before openings. Subtract one 20 square foot door and two 12 square foot windows to get 340 square feet. Two coats require 680 square feet of coverage. At 350 square feet per gallon, the room needs 1.94 gallons, so 2 gallons is the minimum planning order.
If the existing color is dark and the new color is light, add primer or plan for more coverage risk. If the walls are heavily textured, use a lower coverage rate. If several patched areas were sanded, prime those patches so they do not flash through the finish coat.
Room-by-room notes
Kitchens and baths often have less wall area because cabinets, tile, mirrors, and fixtures take space, but cutting in can take longer. Hallways may have many doors and trim lines. Open-plan rooms should be measured by wall section so accent walls, ceilings, and different sheens are not mixed into one gallon estimate.
FAQ
How many coats should I estimate?
Use two coats for most repaints. Add primer for new drywall, stains, bare repairs, glossy surfaces, or major color changes.
Should I subtract windows and doors?
Subtract large openings. For small openings, leaving them in the estimate can provide useful touch-up margin.
What coverage rate should I use?
Use the paint label. If you do not know the product yet, 350 square feet per gallon is a practical planning value.
Does ceiling paint count separately?
Yes. Ceilings use their own area, product, color, and coverage assumptions.
How much paint is needed for trim?
Estimate trim separately by linear feet, profile size, door count, and number of coats.
Should I buy extra paint?
Keep some paint for touch-ups from the same project batch. It helps with future repairs and small missed spots.
Sources and assumptions
Last updated 2026-05-09. This guide uses cited paint calculator references, common interior estimating practice, and editable SupplyCalc assumptions. Product labels, primer requirements, surface condition, and finish quality should control final purchasing.