Painting
Paint Calculator for Room Walls
Estimate wall area and gallons of paint for a rectangular room using wall height, coats, label coverage, openings, and waste. Optional cost uses only the price per gallon you enter.
Calculator inputs
Paint Calculator Results
Results update in your browser as you edit inputs. They are planning estimates, not complete shopping lists.
Enter project dimensions to calculate material quantity.
Assumptions
- The room is treated as a rectangle.
- Doors and windows are subtracted only when you enter counts and average opening areas.
- Ceilings, trim, primer, and surface repairs are not included.
- Coverage per gallon should come from the paint label.
- For buying paint, use the rounded whole-gallon quantity or the container sizes available for your product.
- Cost outputs use only the unit prices you enter.
Formula
- Wall area = 2 x (room width + room length) x wall height.
- Paintable wall area = wall area minus optional door and window area.
- Coated area = paintable wall area x number of coats.
- Gallons needed = coated area divided by coverage per gallon.
- Gallons with waste = gallons needed x (1 + waste factor).
How to Use the Paint Calculator
- Enter room width, room length, and wall height.
- Enter the number of coats you plan to apply.
- Use the coverage per gallon from the paint label, not a generic promise.
- Subtract doors and windows only when you want a tighter wall-area estimate.
- Review gallons before rounding and the rounded whole-gallon equivalent before buying.
Paint Calculator Examples
12 ft x 12 ft room with two coats
A 12 ft by 12 ft room with 8 ft walls has 384 sq ft of wall area. Two coats at 350 sq ft per gallon need about 2.2 gallons before waste, so the whole-gallon equivalent is 3 gallons.
- Wall area: 384 sq ft
- Coated area: 768 sq ft
- Coverage: 350 sq ft/gal
- Rounded whole-gallon equivalent: 3 gal
10 ft x 10 ft room with one coat
A 10 ft by 10 ft room with 8 ft walls has 320 sq ft of wall area. One coat at 350 sq ft per gallon needs about 0.91 gallons before waste.
- Wall area: 320 sq ft
- Coats: 1
- Coverage: 350 sq ft/gal
- Liquid estimate: about 0.91 gal
Bedroom with one door and two windows
A 12 ft by 14 ft bedroom with 8 ft walls has 416 sq ft of wall area before openings. Subtracting one 20 sq ft door and two 15 sq ft windows leaves about 366 sq ft before coats.
- Room perimeter: 52 ft
- Wall area: 416 sq ft
- Openings deducted: 50 sq ft
- Paintable wall area: about 366 sq ft
Units and Parameters Quick Reference
Paint inputs and coverage
Coverage can vary by surface texture, color change, primer, and product type.
| Input | Unit | Planning note |
|---|---|---|
| Room dimensions | ft | Used to calculate wall perimeter and wall area. |
| Wall height | ft | Use the painted wall height. |
| Coats | count | Two coats doubles the coated area. |
| Coverage | sq ft/gal | Use the paint label. |
| Openings | count | Optional rough deductions for doors and windows. |
This calculator estimates wall paint only unless you add your own assumptions for primer, trim, or ceiling paint.
When to use this room paint calculator
Use this page when you are planning wall paint for a rectangular bedroom, office, living room, or similar DIY room and want a gallon estimate before checking product labels.
Keep ceilings, trim, primer, patching materials, rollers, brushes, tape, and drop cloths as separate planning lines. Those materials use different coverage rules and should not be folded into the wall gallon result.
Common room paint planning cases
Use these scenarios to decide which inputs matter before estimating gallons.
| Scenario | Inputs to check | Separate planning line |
|---|---|---|
| Standard bedroom repaint | Room size, wall height, coats, coverage | Trim paint and touch-up supplies |
| Dark color to light color | Lower coverage value and possibly primer | Primer estimate |
| Room with large openings | Door and window deductions | Ceiling paint if included |
| Fresh drywall | Primer and lower first-coat coverage | Drywall primer |
The calculator estimates wall paint gallons. Other paint products and supplies should be estimated separately.
Gallons of paint per square foot
If you want to compare coverage by square foot, convert coats and label coverage into a gallons-per-square-foot planning rate.
Gallons per sq ft = number of coats / coverage per gallon x (1 + waste factor).
Quick paint coverage examples
| Scenario | Gallons per sq ft | Approx. gallons per 100 sq ft |
|---|---|---|
| 1 coat, 350 sq ft/gal, 0% waste | 0.0029 | 0.29 gal |
| 2 coats, 350 sq ft/gal, 0% waste | 0.0057 | 0.57 gal |
| 2 coats, 350 sq ft/gal, 10% waste | 0.0063 | 0.63 gal |
Surface texture, primer, color change, and actual product coverage can change the final quantity.
Example calculation
Example: 12 x 12 room
A 12 ft by 12 ft room with 8 ft walls has 384 sq ft of wall area. Two coats at 350 sq ft per gallon need about 2.2 gallons before waste.
Common mistakes
- Forgetting to multiply by the number of coats.
- Using advertised coverage when a rough surface needs more paint.
- Using the wall result for ceilings, trim, primer, or repairs without separate estimates.
- Comparing costs without entering your own product price.
FAQ
Does this subtract windows and doors?
Yes, if you enter door and window counts with average opening areas. Leave those fields at 0 for a quick full-wall estimate.
Does this include ceiling paint, trim paint, or primer?
No. This calculator estimates wall paint only. Estimate ceilings, trim, primer, and specialty coatings as separate material lines because coverage and product type can differ.
How many gallons of paint do I need for a 12x12 room?
With 8 ft walls, two coats, and 350 sq ft per gallon coverage, a 12x12 room estimates about 2.2 gallons before waste, or 3 whole gallons before door and window adjustments.
What coverage per gallon should I enter?
Use the coverage printed on the paint label for the exact product. Rough walls, patched drywall, textured surfaces, strong color changes, and porous surfaces can need a lower coverage value.
Can I estimate paint material cost?
Yes. Enter your own price per gallon and the calculator multiplies it by the estimated gallons. The site does not fetch store data or service rates.
How many gallons of paint do I need per square foot?
Divide the number of coats by the coverage per gallon. For two coats at 350 sq ft per gallon, the rate is about 0.0057 gallons per square foot before waste.
Does this calculate primer?
No. Primer coverage and need depend on surface condition, color change, and product instructions.
Should I subtract every small window and closet opening?
Not always. For quick planning, many DIY estimates leave small openings in the wall area as a cushion. Subtract large doors, big windows, or built-ins when they remove a meaningful amount of paintable wall.
How do I handle ceiling and trim paint?
Estimate them separately. Ceiling paint uses ceiling area, while trim depends on baseboards, casing, doors, and product coverage. Those surfaces are not part of this wall paint estimate.
Why does the rounded gallon result look higher than the liquid gallons?
Paint is usually purchased in practical container sizes. The calculator shows liquid gallons first, then rounds up to a whole-gallon equivalent for planning.
Related Planning Tools
Use these related calculators when the same project needs another material estimate. Each link opens a browser-based tool with its own assumptions and formulas.