How Much Paint for a Room? (10x12 Bedroom, Bathroom, Garage Examples)
A room-by-room paint estimating guide with gallon amounts for bedrooms, bathrooms, kitchens, living rooms, and garages — including step-by-step formulas and worked examples.
How Much Paint Do I Need for a Room?
A 10x12 bedroom needs 2–3 gallons for walls and ceiling with two coats. A small bathroom needs 1–2 gallons. A 20x20 two-car garage needs 5–8 gallons depending on ceiling height and whether you paint the ceiling. These are the numbers most people search for, and the table below covers every common room type. This is one of the guides on OnSiteCalculator.
For a custom estimate based on your exact dimensions, doors, and windows, use the paint calculator. For coverage rates by paint type and surface, see the paint coverage per gallon guide.
Paint Amounts for Common Room Sizes
All estimates assume 8-foot ceilings (unless noted), standard interior latex at 375 sq ft/gal, two coats, and typical door/window deductions. Ceiling paint is listed separately because not every project includes it.
| Room Type | Dimensions | Wall Area | Ceiling Area | Gallons (Walls, 2 Coats) | Gallons (+ Ceiling) | Notes |
|---|---|---|---|---|---|---|
| Small bedroom | 10 x 10 | ~280 sq ft | 100 sq ft | 1.5–2 | 2–2.5 | 1 door, 1 window |
| 10x12 bedroom | 10 x 12 | ~317 sq ft | 120 sq ft | ~2 | 2.5–3 | 1 door, 1 window |
| Average bedroom | 12 x 12 | ~350 sq ft | 144 sq ft | 2 | 2.5–3 | 1 door, 1–2 windows |
| Master bedroom | 14 x 16 | ~430 sq ft | 224 sq ft | 2.5–3 | 3.5–4 | 1 door, 2 windows, closet door |
| Living room | 15 x 20 | ~500 sq ft | 300 sq ft | 3–3.5 | 4–5 | 2 entry points, 2–3 windows |
| Large living room | 18 x 24 | ~620 sq ft | 432 sq ft | 3.5–4 | 5.5–6.5 | Open plan; subtract any half-walls |
| Small bathroom | 5 x 8 | ~165 sq ft | 40 sq ft | 1–1.5 | 1.5 | 1 door, 1 window. Subtract tub surround |
| Standard bathroom | 8 x 10 | ~230 sq ft | 80 sq ft | 1.5–2 | 2–2.5 | 1 door, 1 window |
| Half bath / powder room | 5 x 5 | ~120 sq ft | 25 sq ft | ~1 | 1–1.5 | 1 door, small or no window |
| Kitchen | 12 x 14 | ~300 sq ft | 168 sq ft | 2–2.5 | 3–3.5 | Subtract cabinets and backsplash |
| Laundry room | 6 x 8 | ~170 sq ft | 48 sq ft | 1–1.5 | 1.5–2 | 1 door; subtract washer/dryer wall |
| Single accent wall | 12 x 8 | 96 sq ft | — | ~0.5 | — | 1 quart may be enough for 1 coat |
| Garage (1-car) | 12 x 20 | ~400 sq ft | 240 sq ft | 2.5–3 | 4–4.5 | 10 ft ceiling; subtract garage door |
| Garage (2-car) | 20 x 20 | ~530 sq ft | 400 sq ft | 3.5–4 | 5.5–7 | 10 ft ceiling; subtract garage door (~130 sq ft) |
| Garage (3-car) | 30 x 20 | ~700 sq ft | 600 sq ft | 4.5–5 | 7.5–9 | 10 ft ceiling; large door opening |
How to read this table: Find your room type and check the “Gallons (Walls)” column for walls only, or the ”(+ Ceiling)” column if you are painting overhead too. These are buy-this-many numbers — already rounded up for waste and practical gallon sizing.
How to Calculate Paint for Any Room (Step by Step)
If your room is not in the table, or your dimensions are different, follow this formula:
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Measure the perimeter. Add up the length of every wall. A 10x12 room: 10 + 12 + 10 + 12 = 44 feet.
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Multiply by wall height. Perimeter × ceiling height = gross wall area. 44 × 8 = 352 sq ft.
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Add the ceiling if painting it. Length × width. 10 × 12 = 120 sq ft.
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Subtract doors and windows. Deduct 20 sq ft per standard door and 15 sq ft per window. Sliding or French doors: 40 sq ft. 1 door + 1 window = 35 sq ft.
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Calculate net paintable area. 352 − 35 = 317 sq ft walls. Add ceiling: 317 + 120 = 437 sq ft total.
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Multiply by coats. Two coats is standard. 437 × 2 = 874 sq ft of coverage needed.
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Divide by coverage rate. Interior latex on smooth drywall: 375 sq ft/gal. 874 ÷ 375 = 2.33 gallons.
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Round up. Buy 3 gallons. The extra covers touch-ups and future repairs.
The formula in one line: (Perimeter × Height + Ceiling − Openings) × Coats ÷ 375 = Gallons
The paint calculator does all of this automatically. Enter your room dimensions, number of doors and windows, and it gives you an instant gallon count with waste included.
Paint for Specific Rooms
Bedrooms and Living Rooms
Standard rectangular rooms are the simplest to estimate. Walls are smooth drywall, ceilings are flat, and there are predictable door and window openings to subtract. Use flat or eggshell finish for walls and flat for ceilings.
For accent walls, figure one wall’s area separately. A 12-foot wall at 8 feet high is 96 sq ft — about one quart for a single coat or half a gallon for two coats. Buy a full quart minimum, as stores do not sell smaller amounts of custom-mixed paint.
Bathrooms
Bathrooms are smaller but have more deductions. Subtract the tub or shower surround if it is tiled (typically 25–40 sq ft depending on size), the vanity mirror area, and any tile wainscoting. A 5x8 bathroom with a tub surround may have only 100–120 sq ft of paintable wall.
Use semi-gloss or satin finish in bathrooms for moisture resistance and easy cleaning. These finishes cover 300–350 sq ft per gallon — slightly less than flat — so adjust your estimate accordingly.
Kitchens
Kitchens have the most deductions: upper and lower cabinets, backsplash, appliance recesses, and windows. A 12x14 kitchen might have 350 sq ft of gross wall area but only 200 sq ft of paintable wall after subtracting cabinets and backsplash.
If you are painting the cabinets too, calculate their surface area separately. Cabinet doors average 4–6 sq ft per door face (front only). A kitchen with 20 cabinet doors has about 80–120 sq ft of door faces plus frame surfaces. Cabinet paint (semi-gloss or gloss) covers 200–250 sq ft per gallon.
Garages
Garages differ from living spaces in three ways: taller ceilings (9–10 feet is common), larger door openings to subtract, and surfaces that may be bare drywall or concrete block instead of finished walls.
A standard two-car garage (20x20) with 10-foot ceilings has about 800 sq ft of gross wall area. Subtract the garage door opening (~130 sq ft for a 16x8 door) and an entry door (20 sq ft), leaving about 650 sq ft. For walls only with two coats: 650 × 2 ÷ 375 = 3.5 gallons. Add the 400 sq ft ceiling and you are at 5.5–7 gallons total.
Bare drywall or concrete block in garages absorbs more paint. Use the lower end of coverage rates (300–325 sq ft/gal) and add a primer coat if the walls have never been painted.
Adding Trim, Doors, and Windows
Trim paint is calculated separately from wall paint because it uses a different finish (semi-gloss or gloss) with a lower coverage rate of 200–300 sq ft per gallon.
Converting linear feet to square feet: Multiply the total linear footage of trim by the board width in feet. Common widths:
- Baseboard (3.5-inch): linear feet × 0.29 ft
- Baseboard (5.5-inch): linear feet × 0.46 ft
- Door/window casing (2.5-inch): linear feet × 0.21 ft
- Crown molding (3.5-inch): linear feet × 0.29 ft
Typical room example: A 10x12 bedroom has about 44 linear feet of baseboard (minus the door opening, so ~40 lf), one door surround (~17 lf of casing), and one window surround (~12 lf of casing). Total trim: about 40 × 0.46 + 29 × 0.21 = 18.4 + 6.1 = 24.5 sq ft. At 250 sq ft/gal, that is about 0.1 gallons per coat — one quart covers the trim in this room with paint to spare.
Doors: A standard interior door is about 20 sq ft per side. If you are painting both sides and all edges, figure 42–44 sq ft per door. One gallon of semi-gloss covers 10–12 complete doors.
For actual trim board widths, the lumber dimensions chart shows nominal vs real dimensions. A “1x6” baseboard is actually 5.5 inches wide — use the actual measurement for your area calculation.
Waste Factor and Primer
Waste
Always add waste to your raw gallon calculation. Paint is lost to roller nap loading, brush marks that need re-rolling, drips, spills, and cut-in overlap.
- 5% waste: Simple rectangular room, experienced painter, roller application.
- 10% waste: Average room with some corners, soffits, or obstacles.
- 15% waste: Heavily textured walls, many obstacles, or first-time painter.
- 20–30% waste: Sprayer application (overspray).
Primer
Primer is a separate purchase and a separate coat. It covers 350–400 sq ft per gallon. You need it for:
- New or bare drywall (PVA primer)
- Patched or repaired areas (PVA primer)
- Dark-to-light color changes (high-build or tinted primer)
- Glossy or previously oil-based surfaces (bonding primer)
Calculate primer the same way as paint: net paintable area ÷ 400 sq ft/gal = gallons of primer. For a 10x12 room with 317 sq ft of walls, you need about 0.8 gallons of primer — buy 1 gallon.
For a full breakdown of coverage rates by paint and primer type, see the paint coverage per gallon guide.
Related Tools
- Paint Calculator — Enter room dimensions and get an instant gallon estimate for interior or exterior projects with waste and primer calculations.
- Paint Coverage Per Gallon Guide — Full coverage rates chart for interior, exterior, and trim by paint type, surface, and finish.
- Drywall Calculator — Estimate sheets and finishing materials for new drywall before priming and painting.
- Flooring Calculator — Calculate square footage for rooms you are also painting.
- Lumber Dimensions Chart — Look up actual board widths for baseboards, casings, and trim.
- Fraction to Decimal Chart — Convert tape measure fractions to decimals for precise wall and trim measurements.
Frequently Asked Questions
Common questions about estimating paint quantities for specific rooms and project types.
How much paint do I need for a 10x12 room?
How much paint do I need for a bathroom?
How much paint do I need for a 20x20 garage?
Do I need primer plus paint for a room?
How much extra paint do I need for trim?
Should I include the ceiling in my paint estimate?
Room Paint Estimates Summary
This guide provides gallon estimates for every common room type, a step-by-step formula for calculating paint for any room, and practical tips for trim, primer, and waste. Use it alongside the paint calculator on OnSiteCalculator for project-specific numbers.
Related Tools
Use the calculators and charts alongside this guide for the fastest workflow.