Estimate how much paint you need for interior and exterior surfaces.
Complete Guide to Paint Estimation and Application
Painting is one of the most impactful and affordable home improvement projects you can undertake. Whether you’re refreshing a single room or repainting your entire home, accurate paint estimation ensures you buy the right amount — avoiding both waste and frustrating mid-project store runs.
Our paint calculator considers wall dimensions, doors, windows, and the number of coats to give you a precise gallon estimate. The calculator uses the industry-standard coverage rate of 350 square feet per gallon for smooth surfaces with quality latex paint.
Paint Finish Guide
| Finish Type | Sheen Level | Durability | Best Rooms | Hides Imperfections |
|---|---|---|---|---|
| Flat / Matte | 0-5% | Low | Ceilings, formal rooms | Excellent |
| Eggshell | 10-25% | Medium | Living rooms, bedrooms | Good |
| Satin | 25-35% | Medium-High | Kitchens, bathrooms, hallways | Fair |
| Semi-Gloss | 35-70% | High | Trim, doors, cabinets | Poor |
| High Gloss | 70-90% | Very High | Accent details, furniture | Very Poor |
Paint Quantity Reference for Common Room Sizes
| Room Size | Wall Area | After Openings | Gallons (2 Coats) | Approx. Cost |
|---|---|---|---|---|
| 8×10 ft (small) | 288 sq ft | ~230 sq ft | 2 gallons | $70-$120 |
| 10×12 ft (medium) | 352 sq ft | ~285 sq ft | 2 gallons | $70-$120 |
| 12×12 ft | 384 sq ft | ~315 sq ft | 2 gallons | $70-$120 |
| 12×15 ft (large) | 432 sq ft | ~365 sq ft | 3 gallons | $105-$180 |
| 15×20 ft (great room) | 560 sq ft | ~470 sq ft | 3 gallons | $105-$180 |
| 20×20 ft | 640 sq ft | ~545 sq ft | 4 gallons | $140-$240 |
| Master bedroom (14×16) | 480 sq ft | ~395 sq ft | 3 gallons | $105-$180 |
| Full bathroom (8×10) | 288 sq ft | ~225 sq ft | 2 gallons | $70-$120 |
| Kitchen (12×14) | 416 sq ft | ~300 sq ft | 2 gallons | $70-$120 |
| Entire home (1,500 sq ft) | ~4,800 sq ft | ~3,800 sq ft | 22 gallons | $770-$1,320 |
Based on 8-foot ceiling heights, standard door and window counts, and 350 sq ft/gallon coverage rate.
Professional Painting Tips
- Prep is 80% of the job. Clean walls, patch holes, sand rough spots, and prime bare surfaces. A smooth, clean surface ensures better adhesion and a professional finish.
- Invest in quality tools. A good brush ($12-$20) and roller ($5-$10) make a dramatic difference in finish quality and ease of application. Cheap tools leave brush marks and lint.
- Always buy slightly more than calculated. Purchase 10-15% extra for touch-ups, waste, and future repairs. Keep leftover paint labeled for quick touch-ups.
- Use painter’s tape strategically. Apply tape to trim, ceiling lines, and any edges you want crisp. Press the edge firmly with a putty knife to prevent bleeding. Remove tape while the final coat is still slightly tacky for cleanest lines.
- Work in sections and maintain a wet edge. Paint one wall at a time, overlapping into the wet edge of the previous section. This prevents lap marks — visible lines where dried paint meets fresh paint.
- Cut in before rolling. Use a brush to paint 2-3 inches around all edges, corners, trim, and fixtures first. Then roll the field immediately while the cut-in paint is wet for seamless blending.
- Use a paint extender in hot or dry conditions. Floetrol (for latex) or Penetrol (for oil-based) extends the working time of paint, reducing brush marks and lap marks in challenging conditions.
- Don’t skip the ceiling. A freshly painted ceiling makes walls look dramatically better. Use a flat white ceiling paint for most rooms — it’s specifically formulated to minimize spatter and hide imperfections.
Frequently Asked Questions
How much paint do I need for a 12×12 room?
For a 12×12 room with 8-foot ceilings, you’ll have approximately 384 square feet of wall area. Subtracting a door (~21 sq ft) and two windows (~30 sq ft), you get about 333 paintable square feet. With 2 coats, you’ll need approximately 2 gallons of paint (1 gallon covers about 350 sq ft per coat).
How many square feet does a gallon of paint cover?
One gallon of standard interior latex paint covers approximately 350-400 square feet per coat on smooth surfaces. Textured walls, bare drywall, and porous surfaces reduce coverage to 200-300 square feet per gallon. Exterior paint typically covers 250-350 square feet per gallon depending on the surface.
Do I need 2 coats of paint?
Two coats are recommended in most situations for optimal coverage, color accuracy, and durability. A single coat is acceptable when painting the same color or a very similar shade over an existing well-prepared surface. Drastic color changes (light to dark or dark to light) may require 3 coats or a tinted primer.
Should I use primer before painting?
Primer is recommended for: new drywall, bare wood, stained surfaces, drastic color changes, glossy surfaces being repainted, and water-damaged areas. Many modern paints include built-in primer (paint-and-primer-in-one), which works well for routine repaints over existing paint in good condition.
What is the difference between flat, eggshell, and satin paint?
Flat (matte) hides imperfections but scuffs easily — best for ceilings and low-traffic areas. Eggshell has a slight sheen and is washable — ideal for living rooms and bedrooms. Satin has a noticeable sheen and is very washable — great for kitchens, bathrooms, and hallways. Semi-gloss and gloss are best for trim and doors.
How long should paint dry between coats?
Latex paint typically needs 2-4 hours between coats at room temperature (60-80°F). Oil-based paint requires 24 hours between coats. High humidity, low temperatures, and thick application increase drying time. Always check the manufacturer’s recommendation on the paint can.
How much does it cost to paint a room?
DIY painting a 12×12 room typically costs $100-$300 for paint and supplies. Professional painting costs $300-$800 for a single room, depending on prep work needed, ceiling height, and your location. Exterior painting is more expensive, typically $1,500-$6,000 for a whole house.
What paint finish is best for bathrooms?
Satin or semi-gloss finishes are best for bathrooms due to their moisture resistance and easy cleaning. These sheens resist mildew and humidity better than flat or eggshell. Use paint specifically formulated for bathrooms when possible, as these contain antimicrobial additives.
How do I calculate paint for a ceiling?
Multiply the room’s length by its width to get the ceiling area in square feet. For a 12×15 foot room, that’s 180 square feet. Divide by 350 (coverage per gallon) and multiply by the number of coats. For this example with 2 coats: 180 × 2 / 350 = approximately 1 gallon.
Can I paint over wallpaper?
While possible, it’s generally not recommended. If you must, ensure the wallpaper is firmly adhered with no peeling edges. Apply an oil-based primer first to seal the paper and prevent bubbling. Sand lightly between primer and paint coats. Results are better with removal, but this method works in a pinch.
How do I estimate paint for trim and doors?
A standard interior door requires about 1/2 gallon of paint (both sides with 2 coats). Window trim averages 0.5 square feet per linear foot. Baseboards are calculated by their height times the room perimeter. Crown molding is similar. Typically, 1 gallon of trim paint covers 200-250 linear feet of standard trim.
What is the best paint for exterior walls?
100% acrylic latex paint is the best choice for most exterior surfaces. It offers excellent adhesion, flexibility, and UV resistance. For wood siding, choose a paint with built-in mildew resistance. For masonry and stucco, use elastomeric paint that bridges small cracks and provides waterproofing.
How long does exterior paint last?
Quality exterior paint lasts 5-10 years on wood siding, 7-15 years on aluminum siding, 15-20 years on brick and stucco. Factors affecting lifespan include sun exposure, weather, surface preparation quality, paint quality, and number of coats. South and west-facing walls fade faster.
How do I prevent brush marks in paint?
Use the right tools: synthetic bristle brushes for latex paint, natural bristle for oil-based. Don’t overload the brush. Apply paint in long, even strokes following the wood grain. Maintain a wet edge and blend into the previous stroke before it dries. For large flat areas, use a roller instead.
What paint sheen is best for hiding wall imperfections?
Flat (matte) paint is the best at hiding wall imperfections because it absorbs light rather than reflecting it. Eggshell is a good compromise between hiding ability and washability. Satin and semi-gloss sheens highlight every bump, nail pop, and drywall seam, so walls must be perfectly smooth for higher sheens.
How much paint do I need for a 1,500 sq ft house interior?
A typical 1,500 square foot home has approximately 4,500-5,500 square feet of paintable wall space (walls only, not including ceilings). With 2 coats, you’ll need about 8-10 gallons of wall paint plus 2-3 gallons for trim. Add 2-3 gallons if painting ceilings. Exact amounts depend on room layout and openings.
What temperature is too cold to paint?
Most latex paints require a minimum temperature of 50°F (10°C) for application and should not be applied if temperatures will drop below 35°F within 24 hours. Oil-based paints can be applied at slightly lower temperatures (40°F minimum). Low temperatures prevent proper film formation and adhesion.
How do I calculate paint for textured walls?
Textured walls require 20-50% more paint than smooth walls depending on the texture depth. Knockdown texture uses about 20% more, orange peel about 25% more, and heavy skip-trowel textures can require up to 50% more paint. Reduce the standard coverage rate (350 sq ft/gal) by the appropriate percentage.
Should I roll or brush walls?
Use rollers for large flat areas — they’re faster and provide a more even finish. Use brushes for cutting in around edges, corners, trim, and detailed areas. The best approach is to brush-cut the edges first, then roll the field while the cut-in paint is still wet to blend seamlessly.
How do I store leftover paint?
Seal the can tightly by placing plastic wrap over the opening before replacing the lid. Store upside down in a climate-controlled area (not garages or sheds with extreme temperatures). Latex paint lasts 2-10 years in storage; oil-based lasts up to 15 years. Label cans with the room, date, and color code.
What is paint coverage rate?
Paint coverage rate is the area one gallon of paint can cover in a single coat. Standard interior latex covers 350-400 sq ft/gallon on smooth surfaces. Primers cover 200-300 sq ft/gallon. Exterior paints cover 250-350 sq ft/gallon. Coverage varies by paint quality, surface porosity, application method, and color.
How do I paint a room with a vaulted ceiling?
Measure the vaulted ceiling area by multiplying the width by the slant height (not the floor-to-peak height). Use an extension pole for the roller. Work in sections, maintaining a wet edge. Use a paint shield or tape at the ceiling-wall junction. Consider using a scaffolding system rather than a tall ladder for safety.
What causes paint to peel?
Common causes include: moisture behind the surface, painting over dirty or chalky surfaces, insufficient surface preparation, painting over incompatible paint types (latex over oil without primer), applying paint in extreme temperatures, and not allowing enough dry time between coats. Proper prep prevents most peeling problems.
How much paint do I need for the exterior of a house?
Measure the total exterior wall area (perimeter × height) and subtract windows and doors. A typical 2,000 sq ft house has about 2,000-3,000 sq ft of paintable exterior surface. With 2 coats and reduced exterior coverage (300 sq ft/gal), you’ll need 13-20 gallons. Add 2-3 gallons for trim in a contrasting color.
What is the best roller nap for painting walls?
For smooth walls: 3/8-inch nap. For slightly textured walls: 1/2-inch nap. For medium textured walls (orange peel, knockdown): 3/4-inch nap. For heavily textured walls or popcorn ceilings: 1-inch or 1.25-inch nap. Thicker naps hold more paint but create more stipple texture on the surface.
How do I paint behind a toilet or radiator?
Use a mini roller with an extension handle or a special radiator brush (a thin, angled brush on a long handle). For areas behind toilets, remove the toilet if doing a full bathroom paint job — it takes 20 minutes and ensures complete coverage. For tight spaces, a paint pad on a stick also works well.
What is VOC in paint and why does it matter?
VOC stands for Volatile Organic Compounds — chemicals that evaporate from paint as it dries, causing that ‘new paint smell.’ High-VOC paints can cause headaches, dizziness, and respiratory irritation. Low-VOC and zero-VOC paints are available and recommended especially for bedrooms, nurseries, and poorly ventilated spaces.
How do I fix drips and runs in dried paint?
Sand the drip smooth with 220-grit sandpaper once completely dry. Feather the edges into the surrounding paint. Wipe away dust with a tack cloth, then touch up with a thin coat of the same paint. For large drips, you may need to prime the sanded area first to prevent a visible patch.
Can I mix different brands of paint together?
Mixing paints of the same type (both latex or both oil-based) and finish from different brands generally works for touch-ups. However, colors may shift slightly due to different pigment formulations. For consistent results on visible areas, use the same brand and batch. Never mix oil-based and latex paints.
How do I paint a straight line between wall and ceiling?
Use painter’s tape applied carefully along the junction, pressing firmly to prevent paint bleeding. Alternatively, master the ‘cutting in’ technique with a quality angled brush: load the brush, place it 1/4 inch from the line, then slowly push toward the junction as you draw a steady line. Practice makes perfect.