Learning how to estimate painting jobs means getting four things right: the surface area, the coverage per gallon, the number of coats, and the prep and labor around them. Paint itself is cheap compared with the labor to apply it, so a quantity error usually costs less than a mistake in production rates or prep. Even so, a wrong gallon count delays the job, and a careless area count is often a sign of other problems. This guide walks through the method for interior and exterior work.
For a complete painting takeoff from your drawings, see our painting estimation service.
Start with the finish schedule and specification
The specification tells you the paint system for each surface: primer, number of finish coats, sheen, product line, and sometimes the dry film thickness. The finish schedule tells you which rooms and surfaces get which system. A project with one standard wall paint is a very different job from one with epoxy in the kitchen, intumescent coating on steel and special finishes in the lobby. Group your takeoff by system, since each has its own coverage, coat count and labor rate.
Check the substrate as well. Drywall, plaster, masonry, wood, metal and previously painted surfaces all need different prep and primers. The level of finish on drywall, described in our post on how to calculate drywall quantities, also affects how many coats are needed for a uniform appearance.
Step 1: Measure the paintable area
- Walls: perimeter × height for each room, or total wall length by height from the plans. Deduct large openings if that is your convention.
- Ceilings: floor area for flat ceilings, plus soffits and bulkheads on their own lines. Exposed structure such as joists and ducts has much more surface than the floor area suggests, so measure it separately and use an area multiplier from your own history.
- Doors: count each door and frame as a unit, with separate prices for each face if the spec requires.
- Trim, base and crown: measure in linear feet.
- Exterior: measure wall area from the elevations, plus fascia, soffits, railings and trim, and add for textured or rough surfaces.
- Miscellaneous: handrails, pipes, grilles, columns and fixtures that are specified as painted.
Step 2: Convert area to gallons
Coverage varies by product and by surface, so use the number on the manufacturer’s product data sheet, not a general figure. As a rough starting point, many interior latex products spread around 350 to 400 square feet per gallon on smooth, primed surfaces. Rougher or more porous surfaces such as block, stucco, raw wood and new drywall absorb more and spread less.
The basic formula is: gallons = area × coats ÷ coverage per gallon. Then add a waste allowance, commonly in the range of 5 to 10 percent, for roller and tray loss, cut-in work and touch-ups.
For high-performance coatings, coverage is tied to film thickness. The theoretical coverage of a gallon is about 1,604 square feet at one mil of dry film at 100 percent solids by volume. So coverage per gallon = 1,604 × volume solids ÷ dry film thickness in mils. A coating with 60 percent solids at a 4-mil dry film gives 1,604 × 0.60 ÷ 4 = about 241 square feet per gallon, before application losses. Real jobs lose more material than that, especially with spray application, so always check the data sheet.
Step 3: Count the coats and the primer
The specification sets the minimum: usually one primer coat and two finish coats on new work, and sometimes only two coats over a previously painted surface in good condition. Where a dark color goes over a light one, or the reverse, an extra coat may be needed for coverage. Price what the spec requires, and call out any assumption you make beyond it.
Step 4: Estimate labor and prep
Labor depends on method (brush, roller or spray), surface, height and access. Production rates in square feet per hour are best taken from your own completed jobs, since they differ by crew and by region. Prep is its own line, and on repaints it can take as much time as the painting itself. Include:
- Patching, sanding, scraping and priming of repairs.
- Caulking of gaps at trim and joints.
- Masking, covering and moving of furniture or fixtures.
- Power washing and surface cleaning for exteriors.
- Lifts, scaffolding or swing stages for high work.
- Night, weekend or phased work in occupied buildings.
- Punch-list touch-up after other trades finish.
For more on rates, burden and productivity, read our guide to construction labor cost estimating. The Painting and Decorating Contractors of America also publishes standards and resources on painting practices.
A worked example
These numbers are illustrative. An office suite has 600 linear feet of 10-foot walls, 4,000 square feet of flat ceiling, and 30 doors that are painted as separate units. The system is one primer coat and two finish coats on walls, and two coats on ceilings with no primer. Coverage is taken as 350 square feet per gallon for all coats.
- Gross wall area: 600 × 10 = 6,000 sq ft.
- Door openings deducted: 30 × 21 sq ft = 630 sq ft, leaving 5,370 sq ft of wall.
- Wall gallons: 5,370 × 3 coats ÷ 350 = 46.0 gal.
- Ceiling gallons: 4,000 × 2 coats ÷ 350 = 22.9 gal.
- Total: 68.9 gal. With 5 percent waste that is 72.3, so order 73 gallons.
Doors, frames, trim, prep and access equipment are then priced on their own lines. Material is often the smaller part of a painting price, which is why the labor assumptions matter more.
Common painting estimating mistakes
- Using one coverage number for every surface and product.
- Ignoring primer, or pricing two coats when the spec requires three.
- Skipping prep, patching and protection on repaints.
- Measuring exposed ceilings by floor area.
- Leaving out lifts, scaffolds and after-hours premiums.
- Not separating doors, trim, specialty coatings and exterior work.
- Forgetting that the drywall finish level, or other trades’ work, can change the number of coats needed.
See also our guide to common estimating mistakes.
Frequently asked questions
How many gallons of paint do I need for 1,000 square feet of wall?
At 350 square feet per gallon and two coats, you need 1,000 × 2 ÷ 350 = 5.7 gallons, so about 6 gallons. You need more if primer is required or the surface is porous.
Do I deduct windows and doors from the wall area?
Many estimators deduct large openings and leave small ones in to cover cut-in work. Whichever method you use, apply it consistently and price doors and trim separately.
How much does prep add to a painting estimate?
It varies widely. New, clean drywall needs little. Old, damaged or glossy surfaces need much more. Estimate prep by surface condition and by your own production history, not as a flat percentage.
Should painting be priced per square foot?
Per-square-foot rates are useful for budgets and for checking a bid, but a detailed estimate should show area, coats, material, labor, prep and access separately.
Get a painting takeoff you can price quickly
We prepare painting takeoffs by room, surface, system and coat, so you can apply your own labor rates and supplier quotes. See our paint estimation service, our drywall estimation for the work that comes before, or the full estimating services list.