Estimating paint needs often frustrates homeowners. You don’t want to run out mid-job, nor waste money on extra cans. Knowing how many square feet one gallon of paint covers is essential for smart budgeting and planning.
In this article, you’ll learn exact coverage ranges, factors that change coverage, how to calculate your room’s needs, and tips to optimize your paint usage. You’ll leave fully confident to buy the right amount of paint in this article.
What’s the Typical Coverage of One Gallon of Paint?
Under ideal conditions, most manufacturers and pros cite that one gallon of interior wall paint covers between 350 and 400 square feet in a single coat.
Premium paints and ideal surfaces may stretch toward 425 square feet, while lower quality paint or tricky surfaces may fall below 350.
For example:
- Sherwin-Williams cites 350–400 sq ft per gallon for typical interior surfaces.
- Some paint brands and estimating guides use 375–400 sq ft per gallon as their standard.
- In practice, many homeowners report 400 sq ft as a usable benchmark under good conditions.
Keep in mind: this estimate is for a single, full coat on a reasonably smooth wall. It assumes the paint is properly applied, not wasted, and the surface is in decent condition.
Factors That Alter Paint Coverage
Coverage doesn’t stay fixed. Several factors push it higher or lower:
Surface texture and porosity
Rough, textured, or porous surfaces absorb more paint. For example, popcorn ceilings, brick, or fresh drywall may require 15–25% more paint than smooth surfaces.
Previous color and required coats
Painting a light color over dark often needs extra coats or primer. If you’re doing two coats, your effective coverage per gallon is halved.
Paint quality and formulation
Higher-end paints use better binders, pigments, and additives that improve hiding power, so they cover more per gallon.
Application method and technique
Rollers, brushes, or sprayers apply paint differently. A heavy roller coat may use more paint than a steady, thin application. Overspray (in spraying) increases waste.
Weather, humidity, and drying conditions
High humidity or cold temperatures may cause paint to absorb or sag, reducing effective coverage.
How to Calculate Paint Needed for a Space
Use a simple method to estimate your paint requirement accurately:
- Measure each wall: width × height (in feet)
- Sum the areas of all walls
- Subtract window and door areas (typically 20 sq ft per door, 15 sq ft per window)
- Multiply by the number of coats you plan to apply
- Divide by the paint’s coverage (e.g. 350–400 sq ft per gallon)
- Add 10% extra for waste, touchups, or miscalculations
Example Calculation
Say you have a room that is 12 ft × 14 ft, with 8 ft ceilings, 1 door, 2 windows, and you plan two coats:
Walls area:
2 × (12 × 8) + 2 × (14 × 8) = 192 + 224 = 416 sq ft
Subtract doors/windows: 416 – (20 + 2×15) = 416 – 50 = 366 sq ft
Two coats: 366 × 2 = 732 sq ft required
Assume coverage 400 sq ft/gallon: 732 ÷ 400 ≈ 1.83 gallons
Add 10% buffer: ~2.0 gallons
So you’d buy 2 gallons. If coverage is less (say 365), you’d need 732 ÷ 365 = 2.0 gallons up front anyway.
Primer vs. Paint Coverage
Primers typically cover less than the final paint. Many primers achieve only 200–300 sq ft per gallon because their goal is to seal and prepare the surface rather than fully hide color. If you prime first, it helps reduce paint waste and enhances adhesion, but you must account for that lower coverage in your planning.
Real-World Variations & Cautions from Professionals
Some painters warn that coverage estimates can be overly optimistic. One commenter noted that 425 sq ft per gallon is “extremely generous” depending on wall conditions. In real jobs, the 350–400 sq ft range is safer to rely on.
If you have textured surfaces or dramatic color changes, plan upward. It’s better to have leftover than to stop mid-wall waiting for another can.
Tips to Maximize Coverage and Minimize Waste
- Prep surfaces: clean, sand, patch cracks, and use primer when needed
- Use quality tools: a proper roller (¾” nap for rough, ⅜” for smooth) helps spread paint evenly
- Apply thin, even coats: avoid dripping or overloading the roller
- Keep a wet edge: working in consistent passes helps avoid rework
- Buy a bit extra: 5–10% more than your calculation covers touchups
- Store leftover paint properly: airtight sealed can, label with date/color
Coverage Expectations by Surface Type
| Surface Type | Approximate Coverage (1 Coat) | Notes |
| Smooth, painted drywall | 350–400 sq ft | Ideal condition |
| Slightly textured walls | 300–350 sq ft | Some extra paint needed |
| Rough or stucco surfaces | 250–300 sq ft | Much more absorption |
| Primer on bare drywall | 200–300 sq ft | Lower coverage than finish paint |
Use the lower end of ranges in your planning to avoid shortages.
When to Expect More or Less Coverage
If you are painting:
- Over dark paint: expect to need extra coats
- New drywall: primer then two finish coats
- Textured or uneven surfaces: assume +20% paint
- Older walls with patches: add more for touchups
Always check the paint can label — many brands specify their own expected coverage range.
Final Checklist for Buying Paint
- Measure all areas precisely and subtract unpainted zones
- Determine how many coats you’ll apply
- Choose a conservative coverage number (e.g. 350 sq ft)
- Divide required sq ft by your coverage per gallon
- Add 10% for buffer
- Round up to the next available container size
Conclusion
While many sources endorse 350–400 square feet per gallon as a rule of thumb, real coverage can change with surface texture, paint quality, color changes and application technique.
By measuring accurately, applying wisely, and allowing extra buffer, you can avoid surprises in your painting project. Use the methods here to confidently purchase just the right amount — not too little, not too much — and get the job done smoothly.