Skip to main content
Practical Tools
homeDIY

Paint Calculator

Estimate exact paint volume required for interior walls and ceilings, factoring in standard door and window deductions and multiple coats.

Unit System

Spreading rates based on Sherwin-Williams and Benjamin Moore architectural paint technical data sheets.

Planning allowance: ~20 sq ft per door (32"×80" nominal plus trim). Accepts area per opening.
Planning allowance: ~15 sq ft per window (3×5 ft nominal double-hung). Accepts area per opening.
Typically 350 sq ft/gal on primed drywall
Coats of Paint:
Estimated Wall Area (Net)
418.0sq ft
Gross wall area: 468.0 sq ft (less 50.0 sq ft openings)
Estimated Paint Required
2.39Gallons
Recommended purchase: 3 full gallon cans
Formula & Arithmetic Breakdown:
1.Gross wall area = 2 × (14 + 12) × 9 = 468.0 sq ft
2.Openings deduction = (1 doors × 20 sq ft) + (2 windows × 15 sq ft) = 50.0 sq ft
3.Estimated net wall area = max(0, 468.0 - 50.0) = 418.0 sq ft
4.Total surface for 2 coats = 418.0 × 2 = 836.0 sq ft
5.Estimated paint required = 836.0 ÷ 350 sq ft/gal = 2.39 Gallons
6.Suggested retail package combination: 2 Gallons + 2 Quarts = 2.50 Gal (0.11 Gal reserve for touchups)
Suggested Package-Size Combination

Suggested Retail Purchase Quantity:

2 Gallons + 2 Quarts

Provides 2.50 Gallons total (0.11 Gal reserve for future wall touchups).

Package Combination Details

Assumes standard retail containers (1 gallon = 4 quarts = 128 fl oz). For fractional needs up to 0.5 gallons, adding 1 or 2 quart cans provides adequate volume while reducing surplus paint. For needs exceeding 0.5 extra gallons (2 quarts), purchasing a full additional gallon is suggested to ensure sufficient coverage and touchup reserve.

Estimation Assumptions & Technical References

This tool provides an approximation for planning and purchasing estimates based on industry data:

  • Coverage Standard: Theoretical spreading rate of 350 sq ft/gal on pre-primed drywall at recommended dry film thickness (Sherwin-Williams & Benjamin Moore Technical Data Sheets).
  • Architectural Openings: Deductions use common trade planning allowances of ~20 sq ft (1.86 m²) per standard interior door and ~15 sq ft (1.39 m²) per double-hung window. Controls accept deduction area per opening and can be customized above. Clamped to ensure net wall area cannot be negative.
  • Texture & Porosity: Unprimed drywall, textured knockdown, or dark-to-light color transitions absorb up to 25% more paint and require a dedicated primer coat.
Evaluated instantly in your browser

Mathematical Formula & Calculation Method

Net Area = (Perimeter × Height) - Deductions | Gallons = (Net Area × Coats) / 350

Formula Components:

  • Wall Perimeter = 2 × (Length + Width)
  • Gross Wall Area = Perimeter × Wall Height
  • Deductions = (Doors × 20 sq ft) + (Windows × 15 sq ft) [Illustrative planning defaults]
  • Net Paintable Area = max(0, Gross Wall Area - Deductions)
  • Paint Required = (Net Paintable Area × Number of Coats) ÷ Spreading Coverage
  • Suggested Package Mix = Whole Gallons + Quarts (for requirements exceeding whole gallons)

How It Works

1

Enter room dimensions: length, width, and wall height in feet (or meters).

2

Input the count of standard interior doors (~20 sq ft planning default) and windows (~15 sq ft default).

3

Select wall texture (smooth primed drywall covers 350 sq ft/gal; textured covers 275 sq ft/gal).

4

Select coats (2 coats recommended for even, durable opacity).

5

View net paintable area, total paint volume, and the suggested Gallon + Quart retail package combination.

Practical Calculation Examples

14×12 ft Bedroom with 8 ft Ceilings (2 coats)

Painting a standard bedroom with 1 door and 2 windows.

Step 1:Gross wall area: 2 × (14 + 12) × 8 = 52 × 8 = 416 sq ft.
Step 2:Deductions: 1 door (20 sq ft) + 2 windows (30 sq ft) = 50 sq ft.
Step 3:Net area: 416 - 50 = 366 sq ft.
Step 4:Two coats: 366 × 2 = 732 sq ft total coverage needed.
Step 5:Gallons required: 732 ÷ 350 = 2.09 gallons.
Step 6:Package Suggestion: Buying 2 Gallons + 1 Quart provides 2.25 Gal (leaving a 0.16 Gal touchup buffer).
Outcome: Buy 2 Gallons + 1 Quart for exact coverage with a touch-up buffer.

Important Assumptions & Estimator Guidance

  • Standard paint spreading rate is 350 square feet per gallon on pre-primed drywall (Sherwin-Williams & Benjamin Moore Technical Specifications).
  • Standard interior door opening deduction is an illustrative planning convention of 20 sq ft (nominal 32"×80" plus casing trim).
  • Standard window opening deduction is an illustrative planning convention of 15 sq ft (nominal 3×5 ft).
  • Package combination guide assumes 1 gallon = 4 quarts; purchasing 1 quart for fractional requirements up to 0.25–0.50 gal provides coverage while minimizing excess leftover paint.
  • Unprimed drywall, textured orange-peel plaster, or dark-to-light color transitions absorb up to 25% more paint and require primer.

Common Pitfalls & Mistakes to Avoid

Purchasing only single-coat volume for bare drywall

Unpainted drywall or dramatic color changes absorb paint rapidly and require at least two full coats plus a primer coat.

Correction: Always calculate for 2 coats when repainting or changing color shades.
In-Depth Companion Guide

How Much Paint Do I Need? A Practical Guide

Calculate exact paint requirements for any room: wall surface area, deductions for doors and windows, coats needed, and coverage per gallon.

Read Companion Guide

Frequently Asked Questions

A standard gallon of architectural interior latex paint covers between 350 and 400 square feet of smooth, pre-primed wall surface.

Related Calculators

Other everyday decision tools that pair well with the Paint Estimator.

homeFlooring

Flooring Calculator

Determine total square footage and material box quantities required for hardwood, luxury vinyl plank (LVP), laminate, or carpet projects.

Instant calculationOpen tool
homeRenovation

Tile Calculator

Calculate exact tile piece counts and square footage for bathroom floors, kitchen backsplashes, and walk-in showers with customizable waste allowances.

Instant calculationOpen tool
homeMasonry

Concrete Calculator

Calculate concrete volume in cubic feet and cubic yards, and determine premix bag quantities for slabs, footings, and patios.

Instant calculationOpen tool