How this is calculated
Wall area follows perimeter × ceiling height, minus standard deductions for doors and windows. Paint volume uses the same coverage rates as the Paint Calculator — about 350 ft² per US gallon per coat.
Labour is entered as a rate per square foot or square metre of wall area. That is how many decorators think about a straightforward box room, though trim, prep, and ceiling work are often priced separately.
Formula & methodology
Net wall area = (2 × (L + W) × H) − door/window deductions. Paint = area × coats ÷ coverage. Total = paint cost + (area × labour rate).
Worked example
A 12 ft × 10 ft room, 8 ft ceilings, 2 coats
- 1.Perimeter = 44 ft; gross wall = 44 × 8 = 352 ft²
- 2.Less one door and two windows ≈ 316 ft² net
- 3.Paint ≈ 1.8 gal at 2 coats
- 4.At $38/gal materials + $2.50/ft² labour → planning total near $900
Frequently asked questions
Is ceiling included?
No — this targets wall area only. Add ceiling square footage separately or bump the labour rate if your quote includes ceilings.
What labour rate should I use?
Rates swing by city and finish level. $2–4 per ft² is a common US planning band for walls in decent condition. UK decorators often quote per room — convert to a per-m² rate for comparison.
Prep and primer?
Not broken out here. Heavy prep, stain blocking, or new plaster may need primer and extra labour — increase the labour rate or materials line.
How does this differ from the Paint Calculator?
The Paint Calculator focuses on how much paint to buy. This one adds a labour line for a full room price check.
Two coats enough?
Most colour changes need two coats. Deep colours, red tones, or covering dark paint may need three — change the coat count.
Exterior painting?
Exterior work has different prep, access, and coverage. Use this for interior box rooms only.
Last updated 2026-09-01. Formulas are planning methods — confirm with a supplier before you order.