PROJECTMETER
Calculators/Paint

Paint Calculator

Estimate paint and primer for walls after doors, windows, coats and waste.

Free · No signup · Reviewed August 22, 2026
Step 1
Set your project size

Use the finished area you plan to cover, then refine the assumptions below.

Step 2 · Visual referenceCheck the active area
Interior room prepared for wall painting with a window and doorway
Gross walls352 ft²Openings36 ft²Net coverage316 ft²

Why it mattersSee which walls count and how doors and windows reduce paintable area.

Reference image; figures update from your measurements.

You’ll need

1.99 gallons of paint
Shopping list
21 gal can paint
11 gal can primer
1 room$126.00 primary material estimate

Project shopping list

Use your result as a starting point, then confirm package coverage, product instructions and local requirements before purchasing.

MaterialPaintPackage1 gal canAllowanceIncluded

How the calculation works

2 × (length + width) × height − openings

Enter each project area, choose the measurement system, then adjust waste and real package coverage. Packaged materials round up so the shopping list never suggests part of a box, sheet or panel.

MEASURE WITH CONFIDENCE

How to use the paint calculator

Measure the room perimeter and wall height, subtract doors and large windows, then account for coats, coverage and waste. The result shows exact paint volume plus complete paint and primer containers to buy.

Formula and guidance reviewed August 22, 2026. Always confirm the final order with product instructions and project requirements.
STEP BY STEP

What to measure

  1. 01

    Measure the room

    Record wall-to-wall length and width at floor level. For an irregular room, add each rectangular section as a separate room.

  2. 02

    Measure wall height

    Measure from the finished floor to the ceiling. Use the tallest height for vaulted or uneven rooms, then adjust the estimate with your own project plan.

  3. 03

    Count large openings

    Enter standard doors and large windows so their approximate areas are removed from the wall coverage.

  4. 04

    Confirm the product label

    Set the number of coats, manufacturer coverage and container size from the paint you actually plan to purchase.

WORKED EXAMPLE

12 × 10 ft room with 8 ft walls

  • 1 door and 1 large window
  • 2 finish coats
  • 350 sq ft per gallon
  • 10% waste
Calculated result

The calculator estimates 1.99 gallons of finish paint. With 1-gallon containers, the shopping list rounds up to 2 paint cans plus 1 primer can.

Try your own measurements ↑
AVOID COSTLY REWORK

Common mistakes before you buy

  • Porous, repaired or strongly contrasting surfaces can reduce real-world coverage.
  • Buy tinted cans from the same batch when color consistency matters.
  • Trim, cabinets and doors need separate surface measurements and may use a different product.
FROM QUANTITY TO BUDGET

Compare the complete project cost

Your material quantity is only one part of a quote. Preparation, removal, access, finishing and local labour can change the installed total.

Paint a room$200–$2,000+Plan room-painting costs by separating coatings, preparation, labour, trim and access.Read cost guide →Paint a home interior$965–$3,089Budget a whole-home interior paint project by wall area, ceilings, trim, coats, repairs and occupied-room logistics.Read cost guide →
MEASURE BEFORE YOU ORDER

Planning guides for this calculator

Use the live model for feedback, then use these guides to verify the dimensions and material assumptions behind the result.

Measure & estimateHow to Measure a Room for PaintMeasure wall and ceiling paint area correctly, subtract sensible openings and turn the result into a usable coating estimate.Read guide →Choose & planPaint Waste Factor and Coat PlanningChoose a realistic paint allowance and coat count without inflating every part of the order.Read guide →Compare materialsEggshell vs Satin vs Semi-Gloss PaintChoose an interior paint sheen from light reflection, cleaning needs, surface condition and room use.Read guide →Specify & buyHow to Choose Interior Paint and PrimerBuild a coating specification from substrate, repairs, stain risk, colour change and room exposure.Read guide →Plan a projectHow to Plan a Bathroom Paint ProjectMeasure bathroom walls and ceiling, choose a moisture-tolerant coating system and sequence repairs, ventilation and painting.Read guide →Avoid failuresHow to Prevent Paint Lap Marks and FlashingPrevent visible overlaps, patch sheen and uneven wall colour through preparation, wet-edge control and consistent application.Read guide →Time the workBest Temperature and Humidity for Interior PaintingPlan ventilation, surface temperature, humidity and recoat windows before opening the first can.Read guide →Protect & maintainHow to Store Leftover Paint for Future Touch-UpsLabel, seal and store matching paint so a future repair has the best chance of blending.Read guide →Manage the projectInterior painting: Budget, Quotes, Safety and CloseoutManage a complete interior painting project from measured quantity and comparable bids through safety checks, maintenance records and final acceptance.Read guide →Worked exampleHow Much Paint for a 10 × 12 Room?Work out wall paint for a 10 ft by 12 ft room with an 8 ft ceiling, one door, one window and two finish coats.Read guide →Worked exampleHow Much Paint for a 12 × 12 Room?Calculate a tight two-gallon wall-paint estimate for a 12 ft square bedroom with ordinary openings and an 8 ft ceiling.Read guide →Worked examplePaint Estimate for a 1,500 Sq Ft HouseUnderstand why 1,500 sq ft of floor area cannot be converted directly into a reliable whole-house paint order.Read guide →
TAKE THE PLAN TO THE SITE

Interactive project checklists

Use the pre-order list before material arrives, then save the inspection and maintenance list for closeout and future care.

PAINTING · READYPaint Order and Delivery ChecklistVerify surfaces, coating system, tint, can sizes and room conditions before paint is opened.Open 12-task checklist →PAINTING · CAREPaint Finish Inspection and Care ChecklistInspect coverage, cut lines and repairs, then document cure and future touch-up stock.Open 12-task checklist →
COMMON QUESTIONS

Paint calculator FAQ

How much area does one gallon of paint cover?

Many interior paints list a range near 350–400 square feet per gallon, but surface texture, application method and product formulation change the result. Use the coverage printed on your chosen can.

Does the paint calculator include the ceiling?

The main estimate covers room walls. Treat the ceiling as another rectangular surface or add a separate room-sized area using a ceiling-specific plan and product.

Why does the shopping list include primer?

Primer is estimated as one coat over the same net wall area. Previously painted walls in good condition may not need a full primer coat, while bare drywall, stains or major color changes often do.

KEEP PLANNING
Drywall CalculatorEstimate net wall and optional ceiling area after doors and large windows.Wallpaper CalculatorEstimate net wall area and complete wallpaper rolls after openings, pattern waste and roll coverage.Room AC BTU CalculatorSize a room air conditioner from floor area, sunlight, regular occupants and kitchen use.

Plan accurately. Build safely.

This calculator is a planning estimate, not engineering or code approval. Follow manufacturer instructions and consult a qualified professional for structural, electrical, gas or permit-sensitive work.