Paint Coverage Calculator
Gallons for Any Room or Surface
Calculate exactly how many gallons of paint you need for any room or surface. Enter your dimensions, substrate type, and number of coats — result appears instantly with PCA Standard P1 spread rates and cost estimate.
Ready to calculate? Enter your room dimensions and surface type below — gallon count appears instantly with PCA benchmark comparison.
Doors/windows deducted automatically (1 door = 20 sq ft, 1 window = 15 sq ft)
PCA Standard P1 — 300–350 sq ft/gal on textured drywall
Standard — new surfaces or colour change
Economy: $25–$35 · Premium+: $40–$55 · Ultra: $75–$110
Enter your room dimensions
to see gallons needed
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The paint coverage formula
Paint coverage is a straightforward calculation once you know the correct spread rate for your substrate. Most estimation errors come from using the theoretical rate printed on the can rather than the real-world rate appropriate to the surface condition.
Core Formula
Gallons = (Surface Area × Coats) ÷ Spread Rate
For a 12 × 10 room with 9ft ceilings: wall area = (2 × 12 + 2 × 10) × 9 = 396 sq ft. Subtract 1 door (20 sq ft) and 2 windows (30 sq ft) = 346 sq ft net. At 325 sq ft/gal (textured drywall) × 2 coats = 692 sq ft ÷ 325 = 2.13 gallons — order 3 gallons. Our paint coverage guide covers this step by step.
PCA spread rates by substrate
The Painting Contractors Association (PCA) Standard P1 establishes spread rates by substrate type. These are practical spread rates accounting for surface absorption — not the theoretical rate on the paint can label, which assumes perfect conditions that rarely exist in the field.
| Substrate | Spread Rate (sq ft/gal) | PCA Prep Level | Notes |
|---|---|---|---|
| Smooth Drywall — Primed | 350–400 | Level 1 | New construction, recently primed |
| Textured Drywall — Standard | 300–350 | Level 2 | Orange peel, skip trowel, light knockdown |
| Stucco / Brick / Masonry | 175–200 | Level 3: Premium | Highly porous — heavy absorption |
| Wood Siding | 250 | Level 4: Showroom | Varies with wood grain and condition |
| Primer — New Surfaces | 200–300 | Varies | Higher absorption than finish coat |
Severely deteriorated surfaces (DSD-3/4 — cracking, peeling, or bare substrate) add a 20% waste factor on top of the base spread rate due to heavy absorption into the exposed surface profile. See our paint coverage calculation guide for DSD assessment.
How many coats do I need?
1 coat: Same colour refresh on a sound DSD-0 surface. Not recommended for colour changes — the new colour will show through without achieving uniform hide.
2 coats: Standard specification for new construction, colour change, or DSD-1/2 surfaces. This is the professional standard for achieving a "properly painted surface" as defined by PCA Standard P1.
3 coats: Drastic colour changes (especially dark to light), DSD-3/4 surfaces after stripping, or where superior durability is specified. Premium one-coat products (Sherwin-Williams Emerald, Behr Dynasty) can substitute for a second standard coat if the first coat achieves full hide.
PCA Standard P1 — what a properly painted surface means
PCA Standard P1 is the industry's definition of a professionally acceptable paint job. It defines a properly painted surface as one that is uniform in appearance, colour, and sheen when viewed without magnification at a distance of 39 inches (1 metre) under finished lighting conditions.
This standard is critically important for contractors — it prevents disputes over imperfections that are only visible under raking light or magnification. Any defect visible at 39 inches under normal finished lighting is a legitimate warranty issue; anything visible only under extreme conditions is not.
2025 paint costs and labour rates
Interior paint pricing in 2025 is segmented primarily by resin quality and one-coat hide capability. The premium tier has expanded significantly as contractors respond to rising labour costs — eliminating one coat of paint saves far more in labour than the price difference between economy and premium products.
| Product Tier | Cost per Gallon | One-Coat Hide | Best For |
|---|---|---|---|
| Economy / Contractor | $25–$35 | No | Primer coats, low-visibility areas |
| Premium Plus | $40–$55 | Partial | Standard residential — 2 coat spec |
| Ultra-Premium | $75–$110 | Yes | 1-coat colour change, commercial contracts |
| Exterior Stain | $45–$70 | Varies | Wood siding, decking, UV resistance |
Labour for painting typically makes up 70% of total project cost. At $2–$5 per sq ft for professional application, a 500 sq ft room costs $1,000–$2,500 in labour per coat. An ultra-premium paint that eliminates a second coat saves $1,000–$2,500 in labour — far exceeding the $30–$60 premium on materials for that room.
Frequently asked questions
How many sq ft does a gallon of paint cover?
On smooth primed drywall, a gallon covers 350–400 sq ft per coat per PCA Standard P1. Textured drywall reduces this to 300–350 sq ft/gal. Stucco and brick run 175–200 sq ft/gal. Wood siding averages 250 sq ft/gal. Never use the theoretical 400 sq ft/gal figure for all surfaces — the substrate makes a major difference.
How many coats of paint do I need?
New construction or painting over a different colour requires 2 coats to achieve uniform hide. Same-colour refreshes on sound existing paint (DSD-0) may need only 1 coat. Severely deteriorated surfaces (DSD-3/4) require 3 coats plus a primer coat in some cases.
What is PCA Standard P1?
PCA Standard P1 defines a properly painted surface as one that is uniform in appearance, colour, and sheen when viewed without magnification at a distance of 39 inches (1 metre) under finished lighting. This is the professional standard for accepting or rejecting paint work on residential and commercial projects.
Should I include doors and windows in my wall area?
Subtract them for precision. A standard door is approximately 20 sq ft, a standard window 15 sq ft. For small rooms with few openings, many professionals skip the deduction — the excess paint is used on touch-ups and stored for future use.
What is the break-even between economy and premium paint?
Premium one-coat paints ($75–$110/gal) eliminate a second application coat. At $2–$5/sq ft contractor labour, one saved coat on a 500 sq ft room saves $1,000–$2,500 in labour. The material premium for the better paint is typically $30–$60 for that room. Premium paint almost always wins on total project cost.
How much extra paint should I buy for touch-ups?
Add 10% for smooth surfaces and 15–20% for textured or porous substrates. Always buy one full extra gallon per colour for touch-up storage — mixed paint stored properly can be used months or years later for repairs, and an exact match is impossible to recreate from a new can.
What is DSD and why does it matter?
DSD (Degree of Surface Degradation) is a 0–4 scale from the MPI Repaint Manual. DSD-0 is sound existing paint; DSD-3/4 is severely deteriorated requiring stripping. Higher DSD ratings require more prep, more coats, and add a 20% waste factor on paint quantity due to increased surface absorption.
How do I calculate paint for a vaulted ceiling?
Measure the actual sloped surface area rather than the floor footprint. For a simple vaulted ceiling, calculate the area of each slope (length × slant height) and sum them. For complex shapes, break the ceiling into rectangles and triangles, calculate each, and total them.
References
Painting Contractors Association. PCA Standard P1 — Residential Repainting. PDCA Professional Painting Standards.
Master Painters Institute. MPI Repaint Manual — Degree of Surface Degradation (DSD). MPI Publications.
Sherwin-Williams. (2025). Professional Product Technical Data Sheets. Sherwin-Williams Company.