Free Paint Calculator for Room Walls, Ceiling, Doors, Windows, Coats, Gallons, and Cost
Use this browser-side calculator to turn measurements and material assumptions into a practical first-pass estimate. Review the formulas, verify units, and confirm product or site details before purchasing or building.
Use the calculator
How to use this calculator
1. Measure consistently
Use the units shown beside each input and recheck measurements before relying on the estimate.
2. Set real assumptions
Use product coverage, waste, density, spacing, or bag yield from the actual material when available.
3. Verify before ordering
Treat the output as a planning number, then compare it with drawings, packaging, supplier data, and site conditions.
12 useful features
Room perimeter
Built into this calculator for a clearer planning workflow.
Wall-height input
Built into this calculator for a clearer planning workflow.
Door allowance
Built into this calculator for a clearer planning workflow.
Window allowance
Built into this calculator for a clearer planning workflow.
Ceiling option
Built into this calculator for a clearer planning workflow.
Coat count
Built into this calculator for a clearer planning workflow.
Coverage input
Built into this calculator for a clearer planning workflow.
Net paintable area
Built into this calculator for a clearer planning workflow.
Calculated gallons
Built into this calculator for a clearer planning workflow.
Whole-gallon guide
Built into this calculator for a clearer planning workflow.
Copy/download
Built into this calculator for a clearer planning workflow.
History/print/reset
Built into this calculator for a clearer planning workflow.
Formula and reference table
| Concept | Formula / meaning | Planning note |
|---|---|---|
| Gross wall area | 2 × (L + W) × height | Rectangular room |
| Opening allowance | doors × 21 + windows × 15 | Approximation only |
| Coat area | paintable area × coats | Coverage demand |
| Gallons | coat area ÷ product coverage | Round purchase quantity appropriately |
Pre-order checklist
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Quick knowledge check
What is the safest way to use a material calculator?
Microlearning guide
Volume is not coverage
Area measures a surface. Volume adds depth or thickness. Material bags, yards, and tons may require a volume conversion.
Rounding changes purchases
Whole boxes, bags, boards, or gallons often require rounding up even when the mathematical result is fractional.
Assumptions drive results
Waste, density, coverage, spacing, and product size can move an estimate more than extra decimal places.
Examples and practical uses
Early planning
Compare material scenarios before requesting supplier quotes.
Purchase cross-check
Compare the calculated quantity with package coverage or bulk-unit recommendations.
Measurement review
Use the formula table to independently reproduce the main calculation.
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Frequently asked questions
How is wall area calculated?
For a rectangular room, gross wall area is perimeter times wall height.
How are doors and windows handled?
This calculator uses approximate allowances of 21 square feet per door and 15 square feet per window. Measure openings directly when precision matters.
Why does paint coverage vary?
Surface texture, porosity, color change, primer, application method, and product formulation all affect real coverage.
Should I round gallons up?
For planning, whole-gallon purchases often require rounding. Actual container sizes and touch-up needs vary by product and project.
Does this include trim paint?
No. It estimates wall and optional ceiling paint only.