How does the Paint Coverage Calculator determine the amount of paint I need?

The calculator uses the total square footage of the walls you input, then divides that by the coverage rate listed on your paint can (typically 350–400 square feet per gallon). It also automatically accounts for the number of coats you plan to apply, multiplying the base requirement by that number, so you get an accurate estimate for your entire project.

What information do I need to provide to get an accurate result?

You'll need to enter the height and width of each wall or the total square footage of the surface, as well as the number of coats (usually 1 or 2). For best accuracy, also specify the paint type (e.g., primer, matte, or gloss) because different finishes have slightly different coverage rates due to texture and absorption. If you have windows or doors, you can subtract their square footage to avoid overestimating.

Does the calculator account for wasted paint or uneven surfaces like textured walls?

Yes, the calculator includes a default waste factor of 10% to cover brush marks, spills, and uneven absorption, which is especially useful for porous or textured surfaces. However, if you are painting highly textured walls like stucco or brick, we recommend adding an extra 10–15% manually because those surfaces can absorb up to 20% more paint than smooth drywall.

Can I use the Paint Coverage Calculator for ceilings, trim, or exterior siding?

Absolutely, you can select the surface type from a dropdown menu, and the calculator adjusts the coverage rate accordingly—ceilings typically cover less due to heavier roller application, while trim requires a different formula because you’re measuring linear feet, not square feet. For exterior siding, we factor in roughness and weather exposure, which reduces coverage per gallon compared to interior walls. Just be sure to measure the correct dimension (area for walls/ceilings, linear footage for trim) to avoid errors.

Paint Coverage Calculator

Last updated: 2026-09-25

Paint Coverage Calculator — Free online paint coverage calculator. Enter wall length and wall height to get instant results.

Inputs

Result

Enter values and press Calculate

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Common Examples — Click to Fill

Wall Length (ft)	Wall Height (ft)	Number of Coats	Paint Type	Doors & Windows (number)
10	2.5	2	1	2
12	2.5	2	1	3
14	2.7	2	1	3
16	2.7	2	1	4
20	3	3	1	4

TL;DR: To calculate the paint needed for a room, multiply the room’s perimeter by the wall height to get the total wall area, subtract the area of doors and windows, then divide by the paint coverage rate (10–12 m²/litre) and multiply by the number of coats—for a 14 m × 14 m square room with 2.5 m walls and 6 m² of openings, you need 134 m² ÷ 11 m²/litre × 2 coats = 24.4 litres, which means 5 cans of 5-litre paint.

What Is the Paint Coverage Calculator?

The Paint Coverage Calculator is a free online tool that estimates the exact amount of paint you need for any interior room. You enter two simple measurements—the total wall length (the perimeter of the room) and the wall height—and the calculator instantly returns the paintable surface area and the recommended litres of paint, including the number of 5-litre cans to purchase. This eliminates the guesswork that leads to either buying too much paint (wasting money) or too little (forcing an inconvenient trip back to the hardware store).

This tool is indispensable for homeowners planning a DIY weekend makeover, professional decorators preparing a quote, or property managers budgeting for a renovation. Instead of relying on rough "one can per bedroom" estimates, you get a precise figure based on the actual geometry of your space. The calculator is built around a standard painting principle: paint coverage is measured in square metres per litre, and most interior walls require two coats for a uniform, durable finish.

Beyond simply counting litres, the calculator also helps you understand the relationship between wall dimensions and paint consumption—a 10 m² room with 4-metre-high ceilings uses nearly twice as much paint as the same floor plan with standard 2.4-metre ceilings. By focusing on wall area rather than floor area, this calculator ensures your estimate is accurate from the start.

How to Use the Calculator

Enter the total wall length (in metres): Walk around the room and measure the full perimeter—add the lengths of all four walls together. For a rectangular room, this is simply 2 × (length + width). For a square room of 14 m per side, the perimeter is 4 × 14 = 56 m.
Enter the wall height (in metres): Measure from the floor to the ceiling using a tape measure. Standard residential ceilings are 2.4 to 2.7 metres, but always measure the actual height, including any variations if the ceiling is sloped.
Click 'Calculate': The tool instantly processes your inputs using the coverage formula below. The results display both the total paintable wall area and the exact litres required for two coats.
Check the output for litres and cans: The calculator shows the total paint required (e.g., 24.4 litres) and the number of 5-litre cans you need (rounded up, e.g., 5 cans). This ensures you always buy enough paint without over-purchasing.

Formula and Calculation Method

The Paint Coverage Calculator uses a straightforward three-step formula. First, it calculates the gross wall area by multiplying the room’s perimeter by the wall height. Second, it subtracts the area of any doors and windows (which you do not paint). Third, it divides the paintable area by the paint's coverage rate and multiplies by the number of coats to get the total litres needed.

The formula in plain language:

Step 1 — Gross Wall Area: Total Wall Length × Wall Height
Step 2 — Paintaable Area: Gross Wall Area − (Door Area + Window Area)
Step 3 — Paint Required: (Paintaable Area ÷ Coverage Rate) × Number of Coats

Worked example with real numbers:

Imagine a square room with each side measuring 14 metres. The perimeter is 4 × 14 m = 56 m. With a wall height of 2.5 m, the gross wall area is 56 m × 2.5 m = 140 m². This room has one standard door (about 2 m²) and one standard window (about 4 m²), totalling 6 m² of openings. The paintable area is therefore 140 m² − 6 m² = 134 m².

Using standard interior wall paint with a coverage rate of 11 m² per litre, and applying two coats, the calculation is: 134 m² ÷ 11 m²/litre = 12.2 litres for one coat, then × 2 coats = 24.4 litres. Since paint is sold in 5-litre cans, you divide 24.4 ÷ 5 = 4.88, and round up to 5 full cans. This is the exact figure the calculator produces.

Practical Examples

Scenario	Wall Length (m)	Wall Height (m)	Openings (m²)	Calculated Paint (2 coats)	5L Cans Needed
Small Bedroom	12	2.4	3	10.7 litres	3 cans
Large Living Room	40	2.7	8	49.5 litres	10 cans
Hallway + Stairwell	25	3.0	5	31.8 litres	7 cans

Example interpretation: For the small bedroom (12 m perimeter × 2.4 m height = 28.8 m² gross, minus 3 m² openings = 25.8 m² paintable), you need 25.8 m² ÷ 11 m²/litre × 2 = 4.7 litres. This is less than a single 5-litre can, but because you need two coats, you must buy one 5-litre can and still have some left over—or mix a smaller 1-litre and 2.5-litre can. The calculator correctly suggests buying 1 can of 5 litres, which is the minimum practical purchase.

Tips for Accurate Results

Never use floor area: The most common mistake is substituting the square footage of the floor for the wall area. A 20 m² floor plan with 2.5 m walls has roughly 50-60 m² of wall area, so using floor area alone will underestimate paint needs by half.
Account for three coats on dark or stained walls: If you are painting a deep red or dark blue over a light primer, or covering water stains, you will likely need three coats, not two. The calculator assumes two coats; multiply the final litre result by 1.5 to adjust for a third coat.
Add 20–30% for rough or porous surfaces: Plaster, brick, or old drywall absorbs significantly more paint than smooth new drywall. If your walls are textured (e.g., orange peel or knockdown finish), increase the coverage rate denominator from 11 to approximately 8-9 m²/litre. For example, 134 m² ÷ 8.5 m²/litre = 15.8 litres per coat instead of 12.2.
Measure wall height correctly: Wall height is not always the distance from floor to ceiling at every point. For sloped ceilings (e.g., attic rooms), use the average height or measure the tallest and shortest points and calculate the mean.
Double-check your perimeter: Walk around with a tape measure, not a laser guess. Include all wall segments, including alcoves, closets with doors, and bump-outs. Do not subtract wall sections behind permanent built-in furniture unless you know you won't paint them.
Remember unit consistency: The calculator uses metres. If you measure in feet, convert to metres (1 foot = 0.3048 m) before entering values. A common error is mixing centimetres for height and metres for length, which skews the area by a factor of 100.

Frequently Asked Questions

Q: How much paint do I need for a 12×12 room with 8-foot ceilings?

For a 12 ft × 12 ft room (3.66 m × 3.66 m), the perimeter is 4 × 3.66 m = 14.64 m. With an 8 ft (2.44 m) ceiling, the gross wall area is 14.64 m × 2.44 m = 35.7 m². Subtracting one door (2 m²) and one window (2 m²) leaves 31.7 m² of paintable wall. Dividing by 11 m²/litre and multiplying by 2 coats gives 5.76 litres. You would need two 5-litre cans (10 litres total) to cover this room with two coats, leaving you with about 4 litres of spare paint for touch-ups. If your walls are dark and require three coats, you will need roughly 8.6 litres, so three 5-litre cans is a safe bet.

Q: Is 1 litre of paint enough for a small bathroom?

In almost all cases, no. A typical small bathroom has a perimeter of about 10 m and a wall height of 2.4 m, giving a gross wall area of 24 m². Even after subtracting a door (2 m²) and a small window (1 m²), you have 21 m² to paint. At 11 m²/litre, you need 1.9 litres for one coat and 3.8 litres for two coats. Therefore, you need at least a 4-litre can or a 5-litre can to do the job properly. One litre covers only about 11 m², which is less than half the paintable area of even the smallest bathroom. Always buy at least 4 litres for any full bathroom repaint.

Q: How many square metres does 5 litres of paint cover with two coats?

A 5-litre can of standard emulsion paint covers approximately 55–60 m² of wall surface with one coat (at 11–12 m²/litre). For two coats, that same 5-litre can covers only half that amount: roughly 27.5–30 m² of wall area. In practical terms, a 5-litre can will paint a small bedroom (around 25 m² paintable) with two coats, but it will not quite cover a medium-sized living room (35–40 m² paintable). If your walls are rough or porous, the coverage drops by 20–30%, so a 5-litre can might only cover 20–24 m² with two coats. Always check the manufacturer's label on the specific paint tin, as premium paints sometimes have higher coverage rates of up to 14 m²/litre.