Paint Coverage Calculator – Simple Way to Plan Your Paint Job
The Paint Coverage Calculator on MyTimeCalculator is designed to answer the most common DIY question: “How much paint do I need?” By combining room dimensions, openings, number of coats and coverage per gallon or liter, the calculator gives a realistic estimate of paint quantity before you buy.
Whether you are repainting a bedroom, refreshing a living room, or planning a full renovation, having a coverage estimate helps you budget accurately, avoid wasted paint and reduce the risk of running out halfway through a wall.
1. How the Paint Coverage Calculator Works
The calculator offers two modes to cover most real-world scenarios:
- Room & Walls: For a simple rectangular room with a consistent wall height. You enter length, width and wall height, plus the number and size of doors and windows. The calculator computes the total wall area, subtracts openings, applies the number of coats, and divides by coverage per gallon or liter.
- Custom Area: For situations where you already know the total paintable area (for example from a plan, specification or another area tool). You enter the area directly, choose the number of coats and specify coverage.
Both modes support feet/gallons and meters/liters, so you can use whichever measurement system you prefer.
2. The Basic Paint Coverage Formula
At its core, paint coverage is based on a simple relationship between area, coverage and number of coats:
(Paintable area × Number of coats) ÷ Coverage per unit
Where:
- Paintable area is the final area after subtracting doors, windows and other non-painted surfaces.
- Number of coats is typically 2 for interior walls, but may be higher for drastic color changes.
- Coverage per unit is usually given on the paint can label (e.g. 350 sq ft per gallon or 10 m² per liter).
The calculator applies exactly this formula and then presents both an exact quantity and a rounded recommendation to make buying decisions easier.
3. Estimating Wall Area from Room Dimensions
For a rectangular room with four walls and a uniform wall height, the total wall area before openings is:
From this wall area, the calculator subtracts standard openings:
- Doors: Typically around 21 sq ft or about 2 m² per standard interior door.
- Windows: Frequently around 15 sq ft or roughly 1.4 m² for a medium-sized window.
You can adjust both door and window areas in the inputs to better reflect your actual space. After subtracting these openings, the result is your paintable area for the walls.
4. Choosing the Right Number of Coats
The number of coats has a direct impact on how much paint you need:
- One coat: Sometimes enough for small touch-ups or when repainting with a very similar color, but may not hide the old color completely.
- Two coats: The most common recommendation for interior walls, giving better coverage, durability and color consistency.
- Three or more coats: Often needed when going from a very dark color to a very light one, or when using specialty paints and finishes.
The Paint Coverage Calculator multiplies the paintable area by the number of coats, so doubling the coats roughly doubles the amount of paint required.
5. Typical Coverage Values – Gallons vs Liters
Different paints and surfaces give different coverage values. Smooth, primed drywall will usually cover more area per gallon than rough, unprimed or textured surfaces. As a starting point:
- Imperial units: Many interior paints advertise around 300–400 sq ft per gallon.
- Metric units: A common rule of thumb is about 8–12 m² per liter.
Always check the coverage figure on your specific paint, primer or specialty coating. For tricky surfaces, it is often safer to use the lower end of the range so you do not underestimate.
6. Step-by-Step: How to Use the Paint Coverage Calculator
- Choose the appropriate tab. Use Room & Walls for a simple room, or Custom Area when you already know the area.
- Select your units. Pick feet/gallons or meters/liters to match your measurements and paint cans.
- Enter dimensions or area. For a room, enter length, width and wall height. For custom area, enter the total paintable area directly.
- Add doors and windows. Specify how many openings you have and adjust the area per opening if your doors or windows are unusually large or small.
- Set the number of coats. Two is typical for most interior jobs; increase the value if needed.
- Enter coverage per gallon or liter. Use the value printed on your paint can whenever possible.
- Click the calculate button. Review the wall area, paintable area, area × coats and the paint quantity in gallons or liters, including the rounded recommendation.
7. Practical Tips for Buying Paint
- Round up to full cans: You cannot buy fractional cans, so the calculator’s rounded recommendation helps you avoid coming up short.
- Plan for touch-ups: Keeping a little extra paint is useful for future repairs or color matching, especially for high-traffic walls.
- Account for surface type: Bare drywall, masonry or heavily textured surfaces can consume more paint than smooth, previously painted walls.
- Use primer for big color changes: A separate primer coat can reduce the total amount of finish paint you need and improve the final appearance.
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Paint Coverage Calculator FAQs
Frequently Asked Questions
Quick answers to common questions about estimating paint coverage, choosing coats and interpreting the calculator’s results.
The calculator uses your measurements, openings, number of coats and the coverage value you provide, so it is as accurate as the inputs. Real-world coverage can vary with surface type, absorption, roller vs spray, and application technique. Treat the result as a practical estimate and, when in doubt, round up slightly to allow for touch-ups and surface variations.
Many interior projects paint both walls and ceiling, but the wall-based room mode in this calculator focuses on the four walls only. To include the ceiling, you can add its area to the total (for example using the Custom Area tab) or run a separate calculation with area equal to length × width for the ceiling.
The most reliable value is printed directly on your paint can or technical data sheet. If you do not have that information, a common assumption for interior wall paint is 350–400 sq ft per gallon or around 8–12 m² per liter on smooth, primed surfaces. For rough, porous or unprimed surfaces, use a lower coverage number to avoid underestimating.
The exact quantity is the mathematical result of the formula and can include fractional gallons or liters. In practice, paint is sold in whole-can sizes. The recommended quantity rounds up to the next whole unit so you have enough paint for your project, while still seeing the underlying exact value for comparison or advanced planning.
Yes, as long as you can approximate the total paintable area and choose an appropriate coverage number. Exterior surfaces, siding and fences often have more texture and weather exposure, so coverage per gallon may be lower than for interior walls. For best results, measure or estimate the area carefully and use the manufacturer’s recommended coverage range for exterior products.
For L-shaped or more complex rooms, you can often break the space into rectangles, calculate the wall area for each section separately and then add them together. Once you know the combined paintable area, use the Custom Area tab with that total. This approach works well for most real-world layouts without requiring a fully detailed drawing.