Paint Gallon Calculator
Square Footage to Gallons — Instantly
Calculate exactly how many gallons of paint you need. Enter your surface area, select a coverage rate, and choose the number of coats — result appears instantly using MPI Repaint Manual benchmarks.
Know your square footage? Enter it below with your coverage rate and coat count — gallon total appears instantly, rounded up per industry standard.
Total paintable area in square feet. Subtract doors (~20 sq ft each) and windows (~15 sq ft each) before entering.
MPI benchmark — previously painted interior wall in average condition
Standard — new surfaces, colour change, or bare substrate
Economy: $25–$35 · Mid-range: $40–$58 · Premium: $70–$127
Enter surface area above
to see gallons needed
Related Construction Calculators
More tools for accurate project estimation
The paint gallon formula
Converting square footage to gallons requires three inputs: the net paintable area, the correct coverage rate for your surface type, and the number of coats specified. The formula is straightforward — but the accuracy depends entirely on using the right coverage rate, which the paint can label almost always overstates.
Core Formula
Gallons = (Area ÷ Coverage Rate) × Coats → Round up to whole gallon
A worked example: a 12×14 room with 9 ft ceilings has a gross wall area of (2×12 + 2×14) × 9 = 468 sq ft. Deduct one door (20 sq ft) and two windows (30 sq ft) = 418 sq ft net. At 350 sq ft/gal with 2 coats: 418 ÷ 350 × 2 = 2.39 gallons — order 3 gallons. Our paint cost calculator carries this result forward into a total material spend.
The formula appears in every professional estimating guide because it is mathematically complete. The only judgment call is the coverage rate. Paint manufacturers print a theoretical spread rate on the can — typically 400 sq ft/gal — which assumes smooth, sealed, previously painted surfaces under ideal application conditions. Real surfaces rarely hit that number. See our guide to calculating paint cost for how surface condition affects the total spend.
Coverage rates by surface type
The MPI Repaint Manual and PCA Standard P1 codify practical coverage rates by substrate. These are field-validated rates that account for surface absorption, texture profile, and real-world application waste — not the theoretical maximum the manufacturer assumes.
| Surface Type | Coverage Rate | Coat Spec | Notes |
|---|---|---|---|
| Smooth primed drywall | 350–400 sq ft/gal | 2 coats standard | New construction, recently primed |
| Previously painted interior wall | 350–400 sq ft/gal | 1–2 coats | Sound existing paint, same or similar colour |
| Orange-peel / light texture | 250–350 sq ft/gal | 2 coats | Texture increases macro surface area ~25% |
| Heavy knockdown / skip trowel | 200–300 sq ft/gal | 2 coats | Significant absorption into texture peaks |
| Flat ceiling (standard) | 350–400 sq ft/gal | 1 coat (refresh) / 2 coats (change) | High-hide ceiling flat formulation |
| Textured / popcorn ceiling | 175–250 sq ft/gal | 2 coats (spray) | Spray application only — roller saturates poorly |
| Smooth vinyl / fiber cement siding | 250–400 sq ft/gal | 2 coats | Exterior acrylic latex |
| Rough stucco / EIFS | 150–250 sq ft/gal | 2 coats | Elastomeric or masonry acrylic required |
| Concrete masonry unit (CMU) | 100–200 sq ft/gal | 2 coats + block filler | Block filler first coat mandatory |
The dramatic difference between smooth drywall (400 sq ft/gal) and CMU block (100 sq ft/gal) is not a function of product quality — it is a function of substrate porosity. CMU block is a sponge; the first coat of block filler is consumed almost entirely filling the pores before any film builds on the surface. This is why the paint coverage calculator separates substrate type from everything else.
The rounding rule — and why it is non-negotiable
Professional estimators always round up to the nearest whole gallon. This is not conservatism — it is a codified industry rule with two distinct technical justifications.
Batch colour consistency: Custom-tinted paint is mixed to a formula at the point of sale. Two separate mixing sessions on the same formula will produce colours that are visually identical under fluorescent store lighting but can show a noticeable difference when applied side by side on a wall under directional natural light. This phenomenon, called metamerism, makes it impossible to perfectly match a mid-job replacement can to the original batch. Running out of paint forces a new batch; the rounding rule eliminates that risk.
Application waste: Roller nap absorbs paint, trays retain residual material, and every opening and closing of a can results in evaporation loss. The PCA estimating standards account for a 10–15% application waste factor built into the spread rate benchmarks. Ordering the exact theoretical quantity ignores this waste and guarantees a shortage.
Rounding Rule
If calculated gallons = 1.15 → order 2 gallons (not 1, not 1.5)
The one exception is large commercial jobs where paint is ordered in 5-gallon buckets. In that case, round up to the nearest full 5-gallon bucket rather than individual gallons. This calculator rounds to the nearest whole gallon, which is the correct unit for residential and light commercial work.
Gallons vs quarts — when to split your order
A gallon of paint costs between $25 and $127 depending on quality tier in 2025. A quart of the same paint typically costs 40–50% of the gallon price — not 25% as the arithmetic would suggest. This price structure creates a specific purchasing strategy for small jobs.
| Calculated Gallons | Recommended Purchase | Rationale |
|---|---|---|
| < 0.5 gal | 1 quart | Full gallon creates excess; quart covers with touch-up buffer |
| 0.5–1.0 gal | 1 gallon | Quart may fall short; gallon provides touch-up reserve |
| 1.0–1.75 gal | 2 gallons | Round up — never order 1 gal + 1 qt (batch risk) |
| 1.75–2.5 gal | 2 gallons + 1 quart | Acceptable split when touch-up storage matters |
| > 2.5 gal | Round up to nearest whole gallon | Standard rounding rule applies |
For any colour used throughout a room or across multiple rooms, order exclusively in full gallons from a single mixing session. The batch-consistency risk of mixing different purchase dates for the same custom colour is too high. The room paint calculator handles multi-surface projects where gallon totals per colour must be aggregated across walls, ceiling, and trim.
Frequently asked questions
How do I calculate how many gallons of paint I need?
Divide your total net surface area by the coverage rate for your surface type, then multiply by the number of coats, and round up to the nearest whole gallon. For example: 500 sq ft ÷ 350 sq ft/gal × 2 coats = 2.86 gallons — order 3 gallons. Always add 10–15% for waste and touch-ups if you want a more conservative buffer.
What is the standard coverage rate for interior paint?
The MPI Repaint Manual and PCA Standard P1 set 350 sq ft per gallon as the practical standard for previously painted interior walls in average condition. Smooth primed drywall achieves 400 sq ft/gal. Textured surfaces (orange peel, knockdown) drop to 250–300 sq ft/gal because the surface texture dramatically increases the actual paintable area beyond the two-dimensional measurement.
Should I round up when buying paint?
Yes — always round up to the nearest whole gallon. This is a codified industry rule, not conservatism. Custom-tinted paint mixed in a second batch can show colour variation under natural light, and application waste (roller nap absorption, tray residue, evaporation) is already baked into the coverage rate benchmarks. Running short mid-job forces a new batch and risks a visible colour mismatch at the re-start point.
What is the difference between coverage rate and spread rate?
Coverage rate and spread rate are the same thing — both refer to the area one gallon of paint covers at the specified dry film thickness. Paint can labels show a theoretical spread rate under ideal conditions; MPI and PCA benchmarks provide practical spread rates accounting for real-world porosity, texture, and application waste. Always use the MPI/PCA benchmark for your substrate rather than the can label figure.
How does texture affect how many gallons I need?
Surface texture is the single most impactful variable in paint coverage. A smooth wall achieves 350–400 sq ft per gallon while heavy knockdown or acoustic popcorn ceilings can drop below 200 sq ft/gal. The texture creates micro-peaks and valleys that multiply the real surface area far beyond the two-dimensional measurement — a wall measuring 100 sq ft on a tape measure may have 125–150 sq ft of actual paintable surface once texture profile is accounted for.
How many gallons do I need for a 10x10 room?
A 10×10 room with 8 ft ceilings has roughly 320 sq ft of wall area (perimeter 40 ft × 8 ft height). After deducting one standard door (20 sq ft) and one window (15 sq ft), the net area is 285 sq ft. At 350 sq ft/gal for 2 coats: 285 ÷ 350 × 2 = 1.63 gallons — order 2 gallons. For a colour that also covers trim and ceiling, use the room paint calculator for a surface-by-surface breakdown.
References
Master Painters Institute. (2025). MPI Maintenance Repainting Manual (RSM). MPI Publications.
Painting Contractors Association. (2023). PCA Standard P1 — Touch Up Painting and Damage Repair, and Definition of a Properly Painted Surface. PCA Industry Standards.
Painting Contractors Association. PDCA Cost and Estimating Guide Volume 1: Practices and Procedures. PCA Professional Painting Standards.
Bureau of Labor Statistics. (2025). Occupational Employment Statistics — SOC 47-2141: Painters, Construction and Maintenance. U.S. Department of Labor.