Paint Calculator
Calculate paint needed for rooms with accurate coverage estimates
Paint Prices (per gallon)
Paint Calculator: Coverage Rates, Gallons Needed & Cost Estimator
Our Paint Calculator takes the guesswork out of your painting project. Enter your room dimensions, number of coats, and paint type to instantly calculate exactly how many gallons (or litres) you need — plus an estimated cost breakdown at your chosen price per gallon.
Paint Coverage Rates by Type & Finish
| Paint Type / Finish | Coverage (sq ft/gal) | Typical Coats | Best Used For |
|---|---|---|---|
| Flat / Matte | 400 sq ft/gal | 2 | Ceilings, low-traffic rooms |
| Eggshell | 350 sq ft/gal | 2 | Living rooms, bedrooms |
| Satin | 350 sq ft/gal | 2 | Kitchens, bathrooms, hallways |
| Semi-Gloss | 300 sq ft/gal | 2 | Trim, doors, cabinets |
| High-Gloss | 250 sq ft/gal | 2–3 | Furniture, accent details |
| Primer | 300 sq ft/gal | 1 | New drywall, bare wood, color changes |
| Exterior Flat | 350 sq ft/gal | 2 | Siding, stucco, masonry |
| Exterior Semi-Gloss | 300 sq ft/gal | 2 | Trim, shutters, doors |
How to Use the Paint Calculator
- Enter room dimensions — input the length, width, and ceiling height of the room in feet (or meters).
- Add doors and windows — specify the number and size of openings to subtract unpainted area; a standard door is ~21 sq ft and a standard window is ~15 sq ft.
- Select paint type — choose your finish (flat, eggshell, satin, semi-gloss, gloss) to use the correct coverage rate.
- Set number of coats — 2 coats is standard for most projects; use 3 if covering a drastically different color or painting on bare surface.
- Enter price per gallon — input your paint cost to get the total budget estimate including a 10% waste buffer.
Example Calculations
Example 1 — Single 12 × 14 ft Bedroom (8 ft ceilings)
- Wall area = 2×(12+14) × 8 = 416 sq ft
- Less 1 door (21 sq ft) + 2 windows (30 sq ft) = 416 − 51 = 365 sq ft
- Eggshell at 350 sq ft/gal × 2 coats = 730 sq ft total coverage needed
- Gallons = 730 ÷ 350 = 2.09 → Round up to 3 gallons (includes waste buffer)
Example 2 — 2,000 sq ft House Exterior
- Siding area (≈ gross wall area minus openings) ≈ 1,400 sq ft
- Exterior flat at 350 sq ft/gal × 2 coats = 2,800 sq ft total
- Gallons = 2,800 ÷ 350 = 8 gallons for walls
- Trim semi-gloss (≈ 350 sq ft) = 350 ÷ 300 × 2 = 2.3 → 3 gallons for trim
Frequently Asked Questions
How many square feet does a gallon of paint cover?
A gallon of interior paint typically covers 350–400 square feet per coat on smooth surfaces. Coverage is lower (250–300 sq ft/gal) for porous surfaces like new drywall, textured walls, or exterior masonry, which absorb more paint. High-gloss finishes also cover less area per gallon. Always check the manufacturer's label for the specific product you are using.
Do I need primer before painting?
Primer is recommended for: new bare drywall (paper absorbs paint unevenly without primer), raw or bare wood, surfaces with stains or smoke damage, drastic color changes (dark to light or vice versa), and patched or repaired areas. Modern paint-and-primer-in-one products can reduce the need for a separate primer coat on previously painted surfaces in good condition. Skip primer only on already-painted walls in similar colors that are clean and undamaged.
How many coats of paint do I need?
Most painting projects require 2 coats for full, even coverage. Use 3 coats when: painting a very dark color over white (or white over dark), covering stains that bleed through, using cheaper paint with lower opacity, or painting on raw/porous surfaces. Allow each coat to dry completely (typically 2–4 hours for latex, 24 hours for oil-based) before applying the next.
How do I calculate paint for walls with doors and windows?
Calculate total wall area (perimeter × height), then subtract openings. Standard door: approximately 20–21 sq ft. Standard window: approximately 12–15 sq ft. Bay window: 20–25 sq ft. Many painters skip subtracting openings and use the overage for touch-ups, which is a practical approach for single-room projects. For large projects with many windows, subtracting is worthwhile to avoid over-purchasing.
Should I buy a pint, quart, or gallon?
Pint (0.125 gal): covers ≈44 sq ft per coat — ideal for accent walls under 100 sq ft, touch-ups, or sample testing. Quart (0.25 gal): covers ≈88 sq ft per coat — good for a small bathroom or closet with one coat. Gallon: covers ≈350–400 sq ft per coat — the most cost-effective choice for rooms. Five-gallon bucket: 20–25% cheaper per gallon — best for whole-house or multi-room projects where you can use the same color throughout.
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