The math
How this estimate works
Paintable area = (perimeter × height + ceiling area − openings) × coats. Gallons = paintable area ÷ coverage per gallon, then add 10%.
This approach turns your inputs into a planning quantity. It does not infer hidden conditions, product-specific installation requirements, delivery minimums, or local taxes. Those checks belong in the final purchase decision.
Worked example
A realistic example
A 12 × 15 ft room with 8 ft walls, 40 sq ft of openings, two coats, and 350 sq ft/gal coverage needs about 4.0 gallons including allowance. Buy 4 gallons if colors and finishes match.
Use the example to audit the logic, then replace every sample input with your own field measurement and current local price.
Avoid rework
Common estimating mistakes
- Using the room floor area instead of wall perimeter
- Forgetting a second coat after a major color change
- Treating manufacturer coverage as exact on porous or textured walls
Before ordering
Practical checks
- Prime new drywall before estimating finish paint
- Keep one labeled quart for future touch-ups
- Use the coverage on the exact product data sheet
Quick answers
Frequently asked questions
How accurate is this paint calculator?
It is a planning estimate based on the measurements and rates you enter. Product specifications, site conditions, taxes, delivery, local labor, and code requirements can change the final quantity or cost.
Should I round up materials?
Yes. The tool rounds indivisible items where appropriate and includes the displayed waste or ordering allowance. Always confirm package quantities and return policies before buying.
Can I use this result as a contractor bid?
No. Use it to set an early budget and compare itemized quotes. A qualified local professional should verify field conditions and scope.
Source logic
How we choose references
We prioritize US government, model-code, trade-association, and manufacturer technical resources. Sources support the safety or estimating convention; your selected product sheet and local authority remain controlling.