Room paint calculator
Room length, width and height, doors, windows and whether to include the ceiling: you get the paintable area, gallons and cans.
Purchase quantity
7.58 l
Net measurement: 6.89 l · Waste 10 %
- Paint2 bucket
- Area to paint34.44 m²
- Litres with waste7.58 l
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How it's calculated (visible formula)
walls = 2 × (length + width) × height − doors × 17.4 sq ft − windows × 15.5 sq ft (+ ceiling); paint = area ÷ coverage × coats
- Net geometric measurement, no waste.
- Adjustable waste % for cuts and breakage.
- Purchase rounded up to sellable units (boxes, bags, buckets, boards).
How to calculate it, step by step
- Measure room length, width and height.
- Count doors and windows.
- Decide whether to paint the ceiling too.
- Work out area and gallons from coverage and coats.
- Round up to cans.
Worked example: 13 × 11.5 × 8.2 ft bedroom, 1 door, 1 window
- ≈ 404 sq ft of wall
- − doors and windows ≈ 371 sq ft
- ÷ 400 × 2 ≈ 1.85 gal; +10% ≈ 2 gal
→ Two 1-gallon cans.
Common mistakes
- Not deducting doors and windows.
- Including the ceiling when it's a different color.
- Forgetting closet interiors.
Pro tips
- Protect floors and furniture and cover outlets and switches.
- Patch cracks and holes and sand before painting.
- Ceiling first, then walls, then trim and doors.
- Pull painter's tape while the paint is still wet.
From calculation to quote
Add labour, overhead and your margin, and generate the professional PDF.
FAQs
- How much paint for a 12 × 12 room?
- About 2 gallons for walls at two coats.
- Standard door size?
- About 32 × 80 in (17.4 sq ft).
- Paint the ceiling too?
- If it's the same color, turn on the ceiling option.
- How long does it take to paint a room?
- A pro takes half a day to a day for an average room at two coats.
- What finish for a bedroom?
- Flat or eggshell; satin in high-touch areas.
- How long between coats?
- Per the label, usually 2–4 hours for latex.
Sources and standards
Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.