ganak.appPaint Calculator
Free paint calculator. Enter room or house dimensions to get exact gallons needed, quart breakdown, primer estimate, and cost — for interior and exterior surfaces.
Living rooms, bedrooms · default 375 sq ft/gal
Room Dimensions
Paint Settings
2 coats · 382 sq ft
Project summary
Area breakdown, gallons, and cost at a glance
What Is a Paint Calculator?
Overview of the tool and what it helps you estimate.
A paint calculator estimates how many gallons (or liters) you need before you head to the store — using room dimensions, number of coats, and coverage rate to give you an exact quantity rounded up to the nearest quart.
350
sq ft / gallon
Standard coverage
2
coats typical
Most interior walls
10%
buffer recommended
Touch-up reserve
Paint Calculation Formulas
Core formulas used for wall area and gallon estimation.
Step 1.Wall area
Step 2.Subtract openings
Step 3.Gallons needed
⌈⌉ means round up to the nearest quart — running short risks a visible dye-lot mismatch.
Coverage by Finish & Surface
How finish type and surface texture affect coverage per gallon.
Flat / Matte
Smooth drywall
Eggshell
Primed walls
Satin
Kitchens, bathrooms
Semi-Gloss
Trim, doors
High-Gloss
Cabinets, accents
Exterior
Siding
Masonry / Brick
Exterior
Textured Walls
Rough surfaces
Always check the label on your specific paint can. Select "Custom coverage" in the calculator to enter your own rate.
Paint Calculator Examples
Sample rooms and projects with gallons calculated.
Small Bedroom
1.75 gal
1 gal + 3 qt
10 × 10 ft, 8 ft ceiling
1 door · 1 window · Eggshell · 2 coats
Standard Bedroom
2.25 gal
2 gal + 1 qt
12 × 12 ft, 9 ft ceiling
1 door · 2 windows · Eggshell · 2 coats
Open-Plan Living Room
3.25 gal
3 gal + 1 qt
20 × 16 ft, 9 ft ceiling
2 doors · 4 windows · Satin · 2 coats
Exterior — 2-Story House
~15 gal
Full gallons
40 × 30 ft, 20 ft walls
3 doors · 8 windows · Exterior · 2 coats
Common Mistakes to Avoid
Quick checklist to prevent ordering the wrong amount.
Using floor area instead of wall area — you paint walls, not the floor.
Forgetting the second coat — always multiply area by number of coats first.
Skipping door and window deductions — standard rooms have ~50–80 sq ft of openings.
Ignoring surface texture — rough walls absorb 30–40% more paint than smooth ones.
Ordering exactly the calculated amount — always buy a half-gallon extra for touch-ups.
Buying from two dye lots — order all gallons at once for a consistent color match.
Pro Tips for Buying Paint
Practical advice for accurate paint estimates and better results.
Use primer on new drywall or bare wood — it reduces topcoats from 3 to 2.
Deep reds, bright yellows, and dark blues often need 3 coats — adjust the calculator.
Store leftover paint in a smaller airtight container labeled with room and color code.
Test a sample patch before buying all your paint — lighting affects how colors look.
A 12-inch roller covers more area per pass than a 9-inch on large walls.
Ask the paint store about mis-tinted "oops" paint — sold at deep discount.
Frequently Asked Questions
Common questions about paint coverage and quantity