Step 1
Measure surfaces
Enter room or building dimensions, or begin with a known paintable area.
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Paint quantity and cost planning
Paint Calculator
Estimate paint and primer for interior rooms, exterior walls, ceilings, and trim. Calculate coats, gallons, quarts, opening deductions, supplies, tax, and material cost.
Project modes
Interior + exterior
Paint quantity
Gallons + quarts
Project estimate
Materials + cost
What this calculator includes
Surface modesroom + exterior
Openingsdoors + windows
Coatingspaint + primer
Containersgallons + quarts
Cost estimatematerials + fees
Inputs
Paint project details
Measure the paintable surfaces, select the number of coats, and enter product coverage and current pricing.
Interior room dimensions
Door and window deductions
Coats and waste
Product coverage
Supplier pricing
Coverage guidance
Coverage varies by paint, surface texture, porosity, application method, color change, and manufacturer. Enter the coverage printed on the exact product.
Results
Paint material estimate
Review paintable area, coats, whole-container quantities, and estimated material cost.
Estimated material total
$285.00
Net wall area
339 sq ft
Wall paint
2 gal + 1 qt
Primer
2 gal
Ceiling paint
1 gal + 0 qt
Trim paint
0 gal + 2 qt
Surface calculations
Gross wall area384 sq ft
Opening deduction45 sq ft
Net wall area339 sq ft
Ceiling area144 sq ft
Total base area483 sq ft
Waste allowance10%
Paint quantities
Wall paint required2.13 gal
Wall paint to purchase2 gal + 1 qt
Wall paint purchased volume2.25 gal
Ceiling paint required0.91 gal
Ceiling paint to purchase1 gal + 0 qt
Ceiling paint purchased volume1 gal
Trim paint required0.26 gal
Trim paint to purchase0 gal + 2 qt
Trim paint purchased volume0.5 gal
Exact primer required1.77 gal
Primer to purchase2 gal
Cost breakdown
Wall paint$108.00
Ceiling paint$38.00
Trim paint$40.00
Primer$64.00
Supplies$35.00
Material subtotal$285.00
Estimated tax (0%)$0.00
Delivery fee$0.00
Additional fees$0.00
Estimated material total$285.00
Cost per square foot$0.59
Planning notes
- • Verify product coverage, required coats, surface condition, and current supplier pricing before purchasing.
How to calculate paint for a project
Measure each paintable surface, subtract applicable openings, multiply the net area by the required number of coats, add an allowance for waste and touch-ups, and divide by the product's stated coverage. Paint and primer should be calculated separately.
Step 2
Select coats and coverage
Enter the required finish and primer coats using the exact product coverage.
Step 3
Add pricing
Enter gallon, quart, primer, supply, delivery, fee, and tax amounts.
Paint calculation formulas
Interior wall area
2 × (length + width) × wall height × rooms
This calculates the gross area of four rectangular walls.
Exterior wall area
2 × (building length + width) × exterior height
This estimates the rectangular exterior perimeter-wall area.
Net wall area
gross wall area − applicable opening area
Door and window deductions are limited so the result cannot become negative.
Coated area
net area × coats × (1 + waste percentage ÷ 100)
Separate coated areas are calculated for wall paint, ceiling paint, primer, and trim.
Paint required
coated area ÷ manufacturer coverage per gallon
Coverage must match the selected product and the surface being painted.
Material total
paint + primer + supplies + tax + delivery + fees
The estimate excludes labor unless labor is included manually as an additional fee.
Why actual paint coverage varies
Rough, textured, porous, unfinished, repaired, or absorbent surfaces may use more coating than smooth previously painted surfaces. Spraying can also have different transfer efficiency than rolling or brushing.
Coverage can change with paint formulation, sheen, application thickness, color contrast, temperature, and surface preparation.
Buying gallons and quarts
The calculator uses gallons for the whole portion of the requirement and quarts for the remaining fractional amount. Four required quarts are converted into another gallon.
Compare actual package prices and product availability before purchasing. Keeping matching leftover paint can be useful for future touch-ups.
Product and safety notice
This calculator provides a planning estimate. Verify preparation, primer compatibility, coverage, recoat times, ventilation, protective equipment, application conditions, lead-paint precautions, disposal requirements, and safety instructions with the product manufacturer and qualified professionals.
Frequently asked questions
How do I calculate how much paint I need?
Calculate the net paintable area, multiply it by the number of coats, add a waste allowance, and divide by the paint manufacturer's coverage per gallon. Round the result to purchasable gallon and quart containers.
How much area does one gallon of paint cover?
Many paints advertise coverage near 350 to 400 square feet per gallon for one coat, but actual coverage varies with the product, surface texture, porosity, color change, application method, and surface condition.
Should doors and windows be deducted from wall area?
Large doors and windows can be deducted for a more precise estimate. Small openings are sometimes left included because touch-ups, spills, surface texture, and leftover paint can consume the difference.
How many coats of paint should I calculate?
Two finish coats are common, but the required number depends on the existing color, new color, paint quality, sheen, substrate, repairs, and manufacturer instructions. Primer may be required separately.
Should I buy gallons or quarts?
Use gallons for most of the required volume and quarts for smaller remaining quantities when that combination is economical and available. Compare container prices because four quarts may cost more than one gallon.
Do I need primer?
Primer is commonly used on new drywall, bare or porous surfaces, repaired areas, stains, major color changes, and surfaces requiring improved adhesion. Follow the coating manufacturer's system requirements.
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