Use this interior paint calculator to estimate wall and ceiling area, paint gallons, primer, and material cost for one room or an entire home. Add each room separately, subtract doors and windows, choose the number of coats, and print a clean project summary.
Rooms
Add one line for each room or paint area.
Paint Purchase Summary
| Room | Wall area | Ceiling area | Coats | Paint gallons |
|---|---|---|---|---|
| Room 1 | 0 sq. ft. | 0 sq. ft. | — | 0 |
This is a planning estimate. Coverage varies by product, surface texture, porosity, color change, application method, and waste. Round up to whole containers, check the product label, and confirm your plan with the paint retailer. Trim, doors, cabinets, and touch-up paint are not included.
How the Interior Paint Calculator Works
Measure the length and width of each room, then enter the wall height. The calculator finds the wall perimeter, multiplies it by the height, and subtracts the door and window allowances. If you select the ceiling option, it also adds length × width as a separate paint area.
Coverage is calculated after the number of coats is applied. Wall and ceiling gallons are kept separate because many projects use different paint products or finishes overhead. Each result is rounded up to the next whole gallon so the purchase summary does not suggest buying a fraction of a standard gallon container.
What to Measure Before Buying Paint
- Room length and width: Measure along the floor, wall to wall.
- Wall height: Measure from the finished floor to the ceiling. For sloped or vaulted rooms, split the walls into simpler sections and add them as separate lines.
- Doors and windows: Count standard openings, or change the default square-foot deduction when your openings are unusually large or small.
- Coats: Two coats are common for a finish change, but the correct number depends on the product, existing color, surface condition, and desired result.
- Ceilings: Include them only when they are part of this paint purchase.
Should You Include Primer?
Primer can be useful on new drywall, repaired areas, porous surfaces, stains, or a major color change. It is not automatically required for every repaint. Check the instructions for the exact coating system you plan to use, and ask the retailer when the existing surface is glossy, damaged, stained, or otherwise difficult to cover.
Plan the Full Painting Budget
The cost estimate above covers paint and optional primer only. A complete painting budget may also include patching compound, caulk, masking materials, drop cloths, rollers, brushes, trays, extension poles, ladders, cleanup supplies, delivery, tax, furniture moving, and labor. Transfer the paint estimate into the Home Project Budget Planner to combine those expenses and track actual spending.
If you are deciding whether the labor savings justify doing the work yourself, compare the full cash cost, time commitment, quote scope, and project risk in DIY vs. Hiring a Painter: A Realistic Cost Comparison.
Before approving the full project, use How to Budget for a Home Project Without Missing Hidden Costs to compare quote scope, deposits, exclusions, repairs, disposal, and a realistic contingency.
Why Your Actual Coverage May Differ
The square-foot setting is adjustable because coverage is not identical across products or surfaces. Texture, porosity, application method, color contrast, overspray, spills, and leftover paint for touch-ups can all change the amount you need. Use the coverage printed on the product label as the final planning number. When multiple containers must match exactly, ask the retailer whether they should be boxed or mixed together for color consistency.
A Better Order for Planning the Job
- Measure every room and decide whether ceilings are included.
- Inspect for holes, stains, peeling, moisture, or loose material before choosing products.
- Confirm paint and primer coverage on the labels.
- Use the calculator to create the purchase estimate.
- Add tools, prep materials, tax, delivery, and labor to the project budget.
- Print the summary and take it to the store or use it when comparing quotes.
This calculator provides a planning estimate, not a product guarantee or professional assessment. Follow manufacturer instructions and address moisture, lead-paint, structural, or other safety concerns with an appropriately qualified professional.