Planning to paint a room or a house

Painting is cheap compared with most home projects, and the preparation is most of the work. The paint you buy is the smaller part of the cost of a bad job, and the cost of running out mid-wall is a visible color mismatch. Work out the area, the number of coats and the trim first, and buy everything at once.

The same steps cover a bedroom and the outside of a house. The exterior adds weather, ladders, and a bigger area.

Step 1: Measure the walls, ceiling and trim

Add up the wall area, subtract large windows and doors, and measure the ceiling and the trim separately. Real rooms are rarely perfect rectangles, so break them into shapes. Paint is sold in gallons that cover a stated area per coat, which is a maximum on smooth, primed walls.

Step 2: Work out the paint and the supplies

The room calculator gives the paint for walls, ceiling and trim, the primer, the roller covers, tape and drop cloths. For a house exterior, count the siding, the trim, the doors and the soffits, and allow extra for rough surfaces such as stucco and for dark-to-light changes.

Step 3: Prepare the surfaces

Wash dirty surfaces, scrape and sand peeling paint, fill holes and cracks, and caulk the gaps at trim and corners. Prime bare wood, stains and patches, and any big color change. In houses built before 1978, treat peeling paint as possibly lead-based and follow the EPA's lead-safe rules or hire a certified contractor.

Step 4: Paint in the right order

Ceilings first, then the walls, then the trim, working from the top down. Cut in the edges with a brush, then roll while the edge is still wet. Two coats give a better and more even color than one thick coat. Outside, paint when it is dry, mild and not in direct sun.

Step 5: Wallpaper, paneling and board and batten

Wallpaper is sold in rolls with a stated coverage after pattern matching, and board and batten is a way to cover a wall in a pattern of boards that you can paint. Both are quantities you can work out from the wall size and the spacing.

Before you start

• The coverage on the paint can, and whether the color change needs a coat of primer.
• Lead-safe practices if the house was built before 1978.
• Weather and temperature limits on the label for outside work.
• Ladders or scaffolding that are safe for the height.
• Extra paint of the same batch for touch-ups.

Mistakes that cost people money

• Skipping the preparation, so the paint peels or shows every flaw.
• Buying paint for one coat when the color change needs two.
• Mixing cans from different batches for one wall. Box them together.
• Painting in direct sun, damp air or when frost is coming.
• Sanding or scraping old paint without checking for lead.

Frequently asked questions