How to use this calculator
- Measure the wall perimeter and average height.
- Subtract doors, windows, and surfaces not being painted.
- Enter finish and primer coat counts.
- Use the product label’s stated coverage.
#2994 · Lifestyle & Home Tool
Interior Painting Material Quantity Calculator
Estimate finish paint and primer volume from room perimeter, wall height, excluded openings, coat counts, and product coverage. The calculator keeps the mathematical gallon requirement separate from whole-container purchasing, helping you compare products without hiding the effect of extra coats or primer.
Calculator
Wall dimensions and coverageFormula
Paintable area = perimeter × height − excluded area
Gallons = paintable area × coats ÷ coverage per gallon
Gallons = paintable area × coats ÷ coverage per gallon
What the result means
The calculated volume is a mathematical requirement before rounding to available container sizes. Finish paint and primer are shown separately.
Coverage varies with porosity, texture, application method, color change, and product. Use the actual label and keep primer and finish products separate.
Example calculation
A 60 ft room perimeter at 8 ft high, less 80 sq ft of openings, leaves 400 sq ft. Two finish coats at 350 sq ft per gallon require 2.29 gallons, normally rounded to 3 whole gallons.
Tips for better results
- Measure gables and unusually shaped sections separately.
- Use lower coverage for rough or porous surfaces.
- Do not subtract every small opening; cutting-in can offset the saved area.
- Round each product up to purchasable container sizes.
- Keep batch numbers consistent when appearance matters.
Frequently asked questions
Should I subtract every window from interior wall area?
Subtract large excluded areas. Very small openings may not reduce paint use much because edge work and application loss remain.
How do multiple coats change the interior painting quantity?
Each coat covers the paintable area again, so required volume increases directly with the coat count.
Should primer use the same coverage as finish paint?
This calculator uses one coverage input for planning. If the labels differ materially, calculate primer separately using its own coverage.
Why should calculated gallons be rounded up?
Paint is sold in fixed container sizes, and running short can create color or finish inconsistencies.
Does sprayer loss appear in the formula?
No separate sprayer-loss factor is included. Reflect expected application loss by using a conservative coverage rate.
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Coating quantity variables
| Variable | Unit and purpose |
|---|---|
| Paintable area | Square feet after exclusions |
| Coverage | Square feet per gallon per coat |
| Coats | Separate counts for finish and primer |