Paint Calculator — How Much Paint Do I Need?
Estimate gallons of paint and primer for walls and ceilings. Enter room dimensions, deduct doors and windows, pick coats and surface type, and get an instant materials and cost estimate.
Paint Calculator
Paint Coverage Rates
Coverage depends on the surface. Use the right number in the calculator to avoid under- or over-buying.
| Surface | Coverage (sq ft/gal) | Coverage (m²/L) |
|---|---|---|
| Smooth, previously painted | 350–400 | 8.6–9.8 |
| New drywall (primed) | 350 | 8.6 |
| Bare drywall (no primer) | 250–300 | 6.1–7.4 |
| Textured walls (orange peel, knockdown) | 200–300 | 4.9–7.4 |
| Rough / exterior / masonry | 150–250 | 3.7–6.1 |
How to Measure a Room for Painting
- Measure the perimeter: add up all wall lengths (or 2 × (length + width) for a rectangular room).
- Multiply by the ceiling height to get total wall area.
- Add ceiling area (length × width) if you’re painting the ceiling too.
- Subtract openings: standard door = 21 sq ft (1.95 m²), standard window = 15 sq ft (1.39 m²). Skip tiny openings under 5 sq ft.
- Multiply by the number of coats (usually 2).
- Divide by the coverage rate (350 sq ft/gal typical) and round up.
Imperial example: 12×12 ft room, 8 ft ceiling, 1 door, 2 windows, 2 coats, 350 sq ft/gal. Perimeter: 48 ft. Wall area: 384 sq ft. Deductions: 21 + 30 = 51 sq ft. Net: 333 sq ft × 2 = 666 sq ft ÷ 350 = 1.9 → 2 gallons.
Metric example: 3.7×3.7 m room, 2.4 m ceiling, 1 door, 2 windows, 2 coats, 8.6 m²/L. Perimeter: 14.8 m. Wall area: 35.5 m². Deductions: 4.7 m². Net: 30.8 m² × 2 = 61.6 m² ÷ 8.6 = 7.2 → 8 L (~2 US gallons).
Paint Types and Finishes
- Flat / Matte: no reflection, hides imperfections best. Bedrooms, ceilings, low-traffic walls. Harder to clean.
- Eggshell: soft sheen, slightly washable. Living rooms, dining rooms, hallways — the most versatile interior finish.
- Satin: moderate sheen, durable, easy to clean. Kitchens, bathrooms, kids’ rooms, trim.
- Semi-gloss: reflective, very washable. Doors, trim, windows, cabinets, bathrooms.
- Gloss: highest sheen, hardest finish. Furniture, high-end trim, front doors.
- Latex (water-based): low odor, dries fast, easy cleanup with water. Standard for interior walls.
- Oil / alkyd: durable, levels smoothly, longer dry time. Trim and cabinets when maximum hardness is needed.
Primer Guide
Primer improves adhesion, seals porous or stained surfaces, and lets color paint cover in fewer coats. Coverage is typically ~300 sq ft/gal (7.4 m²/L).
- Use primer when: painting bare drywall, bare wood, water-stained areas, glossy surfaces (sand first), dark-to-light color changes, or patched repairs.
- Skip primer when: repainting the same color, touching up, or painting over clean, flat latex in good condition.
- Types: latex (general purpose), oil / shellac (stain blocking, odor blocking), bonding (glossy or slick surfaces), PVA (new drywall, cheapest).
- Paint-and-primer-in-one: works for moderate color changes over painted surfaces. Not a substitute for dedicated primer on bare or stained substrates.
Frequently Asked Questions
How much paint for a 12×12 room?
A 12×12 ft room with 8 ft ceilings has 384 sq ft of wall. After deducting one door (21 sq ft) and two windows (30 sq ft) = 333 sq ft net. With 2 coats and 350 sq ft/gal coverage: 333 × 2 ÷ 350 = 1.9 gallons → 2 gallons. Add 2 gallons of primer if the walls are bare drywall or heavily stained.
How many coats of paint do I need?
Most jobs need 2 coats — base + finish — for even coverage. Use 1 coat only for refreshing the same color on a smooth surface. Use 3 coats when painting light over dark, when the color is very saturated (deep reds, yellows), or when the surface is highly porous.
Does a gallon of paint cover 400 sq ft?
One gallon typically covers 350 sq ft on smooth, previously painted walls. 400 sq ft is the high end — achievable only on a perfectly flat, primed surface with a high-quality paint. Textured, rough, or unprimed surfaces drop coverage to 200–300 sq ft/gal.
Do I need primer if the walls are already painted?
Usually no — if the existing paint is in good condition, clean, and you’re staying with a similar color, skip primer. Use primer when covering bare drywall, stains, water damage, dark-to-light color changes, or glossy surfaces (sand first). A paint-and-primer-in-one product also works for moderate cases.
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- Area Unit Converter — convert between square feet, square meters, acres, hectares
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Coverage rates are industry averages and vary with paint brand, surface texture, and application method (brush vs roller vs spray). Prices are 2026 US national averages — regional and premium-brand variation is common. Add 10–15% extra for touch-ups. Always check the specific coverage printed on the paint can label.
