Paint Calculator
Use this free paint calculator to find out exactly how many gallons of paint you need for any room. Enter your room length, width, and ceiling height, select the number of coats, and the calculator instantly tells you how many gallons to buy — with door and window deductions already accounted for.
Gallons = Wall Area × Coats ÷ 400 sq ft per gallon
Based on 400 sq ft coverage per gallon (standard) · Each door/window deducts 20 sq ft · Always round up to the nearest full gallon
Estimates based on 2026 US average pricing. Coverage varies by paint brand and surface texture.
How Does the Paint Calculator Work?
This paint calculator estimates how many gallons of paint you need for any room based on wall dimensions, ceiling height, number of coats, and deductions for doors and windows. It uses the industry-standard coverage of 400 square feet per gallon and includes an estimated paint cost based on your selected paint type.
Steps:
- Enter your room length, width, and ceiling height in feet.
- Enter the number of doors and windows — each deducts approximately 20 sq ft from paintable wall area.
- Select the number of coats — 2 coats is standard for most paint jobs.
- Select your paint type to get an estimated cost range.
- Get instant results — gallons needed, wall area, paintable area, and estimated paint cost.
Always round up to the next full gallon when buying paint. Having a little extra lets you touch up scuffs and scratches for years without trying to match a color from a different batch.
Paint Coverage Chart
How many gallons do you need? Use this quick reference chart for common room sizes at standard 9 ft ceiling height, 2 coats, with 2 doors/windows deducted.
| Room Size | Wall Area | 1 Coat | 2 Coats | 3 Coats |
|---|---|---|---|---|
| Small bedroom (10×10) | 320 sq ft | 1 gallon | 2 gallons | 3 gallons |
| Standard bedroom (12×12) | 392 sq ft | 1 gallon | 2 gallons | 3 gallons |
| Large bedroom (14×14) | 464 sq ft | 2 gallons | 3 gallons | 4 gallons |
| Living room (16×20) | 604 sq ft | 2 gallons | 4 gallons | 5 gallons |
| Large living room (20×24) | 756 sq ft | 2 gallons | 4 gallons | 6 gallons |
| Full house interior | ~2,000 sq ft | 5 gallons | 10 gallons | 15 gallons |
*Based on 9 ft ceilings, 2 doors/windows per room, 400 sq ft coverage per gallon. Always buy one extra quart as backup.
Paint Cost by Type (2026)
Paint prices vary significantly by brand, quality, and finish. Here's a breakdown of 2026 US average pricing per gallon and estimated cost to paint a standard 12×12 bedroom (2 coats).
| Paint Type | Cost per Gallon | 12×12 Room (2 coats) | Best For |
|---|---|---|---|
| Standard / Budget | $25 – $35 | $50 – $70 | Rentals, temporary spaces |
| Mid-Range | $35 – $55 | $70 – $110 | Most interior rooms |
| Premium | $55 – $80 | $110 – $160 | Living areas, one-coat coverage |
| Exterior Paint | $40 – $70 | $80 – $140 | Outdoor surfaces, siding |
| Primer | $20 – $40 | $40 – $80 | New drywall, dark color changes |
Mid-range paint (brands like Behr Premium Plus, Sherwin-Williams SuperPaint) offers the best balance of coverage, washability, and cost. Premium paints often cover in one coat, saving you labor time — making the higher price worth it for large rooms.
Example Calculation
You want to paint a 15 ft × 12 ft room with 9 ft ceilings, 2 doors/windows, 2 coats, mid-range paint.
Perimeter = 2 × (15 + 12) = 54 ft
Wall area = 54 × 9 ft = 486 sq ft
2 openings × 20 sq ft = 40 sq ft
Paintable area = 486 − 40 = 446 sq ft
446 ÷ 400 = 1.12 gallons per coat
× 2 coats = 2.23 gallons → round up to 3 gallons
3 × $35 = $105 | 3 × $55 = $165
Paint cost: $105 – $165
Paint Buying & Application Tips
Choosing the Right Finish
| Finish | Sheen Level | Best Rooms | Washability |
|---|---|---|---|
| Flat / Matte | None | Ceilings, low-traffic rooms | Poor |
| Eggshell | Low | Living rooms, bedrooms | Good |
| Satin | Medium | Hallways, kids' rooms | Very Good |
| Semi-Gloss | High | Kitchens, bathrooms, trim | Excellent |
| Gloss | Very High | Trim, doors, cabinets | Excellent |
Do I Need Primer?
You need primer when: painting new drywall, covering a dark color with a lighter one, painting over stains or water damage, or painting bare wood or metal. Skip primer when: repainting a similar color over a clean, previously painted surface — especially if using a paint-and-primer product.
Application Tips
- Use a roller for large flat surfaces (walls, ceilings) and a brush for cutting in edges, corners, and trim.
- Apply paint in a W or M pattern with the roller, then fill in without lifting — this prevents lap marks.
- Let the first coat dry completely (2–4 hours minimum) before applying the second coat.
- Paint from top to bottom — ceiling first, then walls, then trim.
- Use painter's tape on trim, baseboards, and ceiling lines for a clean edge.
This calculator estimates wall paint only. Add 1 gallon of ceiling paint per 400 sq ft of ceiling area, and 1 quart of trim paint per room for baseboards, door frames, and window casings.