Paint Calculator
Estimate how many gallons of paint you need for walls and ceilings. Automatically subtracts doors and windows, calculates primer, and estimates total cost including supplies.
Quick rule of thumb: One gallon of paint covers approximately 350–400 sq ft per coat. Most rooms need 2 coats. A standard 12×12 room with 8-foot ceilings has about 384 sq ft of wall area (minus doors/windows ≈ 320 sq ft) = roughly 2 gallons for 2 coats.
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| Item | Quantity | Est. Cost |
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How to Calculate Paint: The Complete Guide
Paint coverage depends on four factors: the area to be painted, the number of coats, the paint's spreading rate (which varies by quality and type), and the surface texture. The standard spreading rate for interior latex paint is 350–400 square feet per gallon per coat on smooth drywall. Textured surfaces, bare wood, or porous masonry may absorb 20–40% more paint, reducing coverage to 250–300 sq ft per gallon.
Paint Formula
Wall Area = 2 × (Length + Width) × Height
Subtract: Doors (21 sq ft each) + Windows (12 sq ft each)
Paintable Area = Wall Area − Openings
Gallons = (Paintable Area × Coats) ÷ 350
Example: 12×12 room, 8 ft ceilings, 1 door, 2 windows, 2 coats
Walls = 2 × (12+12) × 8 = 384 sq ft
Subtract = 21 + (2 × 12) = 45 sq ft
Paintable = 339 sq ft × 2 coats = 678 sq ft ÷ 350 = 1.94 gallons (buy 2)
Paint Coverage by Type and Finish
| Paint Type | Coverage (sq ft/gal) | Best For | Avg. Price/Gallon | Dry Time |
|---|---|---|---|---|
| Flat / Matte Latex | 350 – 400 | Ceilings, low-traffic rooms | $25 – $40 | 1 hour |
| Eggshell Latex | 350 – 400 | Living rooms, bedrooms | $30 – $45 | 1 hour |
| Satin Latex | 350 – 400 | All-purpose, kitchens, hallways | $30 – $50 | 1 hour |
| Semi-Gloss Latex | 350 – 400 | Bathrooms, kitchens, trim | $35 – $55 | 2 hours |
| High-Gloss Latex | 300 – 350 | Doors, cabinets, trim | $40 – $60 | 2–4 hours |
| Primer (latex) | 300 – 350 | New drywall, dark→light changes | $20 – $35 | 1 hour |
| Ceiling Paint | 350 – 400 | Ceilings (ultra-flat, drip-resistant) | $25 – $40 | 1 hour |
| Exterior Latex | 250 – 350 | Siding, outdoor structures | $35 – $60 | 4–6 hours |
Coverage assumes smooth, primed drywall. Reduce coverage 20–30% for textured walls, bare wood, or masonry. Sources: Sherwin-Williams, Benjamin Moore, Behr product specifications.
Paint Finish Guide: Choosing the Right Sheen
| Finish | Sheen Level | Washability | Hides Imperfections? | Recommended Rooms |
|---|---|---|---|---|
| Flat / Matte | 0–10% | Poor | Excellent | Ceilings, master bedrooms, formal rooms |
| Eggshell | 10–25% | Fair | Good | Living rooms, dining rooms, bedrooms |
| Satin | 25–35% | Good | Moderate | Kitchens, hallways, kids' rooms, all-purpose |
| Semi-Gloss | 35–70% | Very Good | Low | Bathrooms, kitchens, trim, baseboards |
| High-Gloss | 70–90% | Excellent | Very Low | Doors, cabinets, furniture, accents |
Interior Paint Cost Breakdown (National Averages 2025)
| Room Type | Avg. Size | Gallons (2 coats) | DIY Material Cost | Professional Cost |
|---|---|---|---|---|
| Bedroom (12×12) | ~320 sq ft walls | 2 gallons | $70 – $100 | $300 – $600 |
| Living Room (15×18) | ~480 sq ft walls | 3 gallons | $105 – $150 | $450 – $850 |
| Kitchen (12×14) | ~300 sq ft walls | 2 gallons | $70 – $110 | $350 – $700 |
| Bathroom (8×10) | ~180 sq ft walls | 1 gallon | $35 – $60 | $200 – $400 |
| Average Full Interior | ~2,300 sq ft walls | 7–10 gallons | $250 – $500 | $2,000 – $5,500 |
Professional costs include labor, prep, primer, paint, and cleanup. Sources: HomeAdvisor, Angi, Painting Contractors Association. DIY costs are paint + supplies only.
Paint Quality: Does Expensive Paint Actually Perform Better?
Consumer Reports tested 184 interior paints in their 2024 evaluation and found that premium paints ($40-70/gallon) provided measurably better coverage, washability, and durability compared to budget paints ($20-30/gallon). The top-rated paints covered completely in a single coat, while budget paints required 2-3 coats to achieve the same opacity — meaning the "cheaper" paint often costs more per square foot after accounting for additional gallons and labor time.
The Painting Contractors Association (PCA) reports that paint accounts for only 10-15% of a professional painting project's total cost, with labor comprising 75-85%. Upgrading from budget to premium paint adds roughly $50-100 to a room project but can save an entire coat of labor — often a net savings for professionals and a significant time savings for DIYers.
VOC Levels and Indoor Air Quality
Volatile Organic Compounds (VOCs) in paint evaporate during and after application, contributing to indoor air pollution. The EPA regulates VOC limits: flat paints ≤ 250 g/L, other finishes ≤ 380 g/L. However, many modern paints are zero-VOC or low-VOC (≤ 50 g/L), which the EPA considers safe for immediate occupancy.
A 2022 study in Indoor Air found that zero-VOC paints produced 80% lower total VOC concentrations compared to conventional paints 24 hours after application. For bedrooms, nurseries, and rooms with poor ventilation, zero-VOC paints are strongly recommended. Adequate ventilation (open windows, fans) during and for 72 hours after painting reduces VOC exposure regardless of paint type.
For room measurements, use our Square Footage Calculator. For material cost comparisons, see the Discount Calculator. Calculate the area of irregular wall sections with the Area Calculator.
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