Start with paintable area, not floor area
For four walls, gross wall area is 2 × (length + width) × height. Subtract doors and windows, then add the ceiling or trim only when they are part of the job. QuoteCoat keeps those surfaces separate because walls, ceilings, and trim commonly use different products and production rates.
The five cost buckets
Protection and setup
Moving or covering furniture, masking, floor protection, and daily cleanup consume real crew time.
Surface preparation
Patching, sanding, caulk, stain blocking, and moisture damage can cost more than rolling the finish coat.
Paint and sundries
Product line, sheen, color change, primer, tape, plastic, rollers, and disposal all affect materials.
Application labor
Ceilings, detailed trim, stairwells, texture, occupied rooms, and additional coats reduce production speed.
Business overhead
Insurance, travel, estimating, payroll costs, warranty, scheduling, and profit belong in a professional price.
Compare bids on identical scope
Ask every painter to state the surfaces, visible repairs, number of coats, primer conditions, exact paint line or allowance, furniture handling, protection, cleanup, timing, warranty, and exclusions. A lower total is not a bargain if it omits the prep or second coat priced by another bidder.