You have measured the length and width of the room, but those figures do not tell you how much wall area you are going to paint. If you buy based only on the floor area, you may run out of paint halfway through the second coat or end up with several unopened liters.
To calculate it correctly, you need to measure the walls, decide whether you will paint the ceiling, and convert the resulting square meters into liters. PaintUber uses a simple guideline for homeowners: 1 liter for every 5 m² of surface area finished with two coats and a small margin.
Quick answer: how much paint do I need per square meter
This is the complete calculation for buying the right amount:
- Decide whether you are going to paint only the walls or also the ceiling.
- Measure the width and height of each wall in meters.
- Multiply width by height to get the square meters of each wall.
- Subtract doors and windows only if their dimensions are significant.
- Add up all the surfaces that will have the same color.
- Divide the result by 5 to calculate the liters needed for two coats with a margin.
- Round up according to the available sizes and calculate each color separately.
The direct answer is, therefore, 1 liter for about 5 m² of wall when you are going to apply two coats. A 2 L kit covers approximately 10 m² of wall and a 4 L kit, about 20 m².
Do not use the floor area as if it were the wall area. A room with a small floor plan can have a lot of surface area to paint if the ceiling is high, and an open-plan room may have less wall than expected.
Where does the paint calculation per square meter come from
The mineral paint sold by PaintUber has an indicated coverage of 10 to 12 m² per liter and coat. That figure corresponds to a single application. Since a room usually receives two coats, you have to count the same surface twice.
To plan the purchase, the prudent reference of 5 m² per liter is used. It is not calculated with the most favorable extreme of 12 m² per liter and coat. This leaves a certain margin for the paint that remains in the roller and the tray, occasional touch-ups, and small differences in absorption between areas of the same wall.
The calculation can be expressed as follows:
Liters needed = square meters you are going to paint ÷ 5
If you have 20 m² of wall, the operation is 20 ÷ 5 = 4 L. If you have 30 m², you will need 6 L. The reference already accounts for two coats, so you should not multiply the result by two again.
It is advisable to distinguish this purchase calculation from the technical coverage per coat. Using 10 or 12 m² per liter directly for the entire room would give an amount intended for a single layer. That error usually appears when reading the coverage on the container without taking into account the number of coats.
The surface also influences. A uniform wall allows the paint to be spread more evenly than one with repairs, very porous areas, or reliefs. There is no need to invent a different coefficient for each case: measure carefully, work with 5 m² per liter, and round the purchase up to the available size.
How to measure the walls to calculate how much paint you need
Measure in meters and write down each wall separately. Although two walls may look the same, checking both avoids errors in rooms with recesses, built-in wardrobes, or pillars.
For a rectangular wall, multiply its width by its height:
Wall surface area = width × height
A wall 3.60 m wide and 2.50 m high has 9 m². If the opposite wall has the same dimensions, both add up to 18 m².
You can save time by calculating the perimeter of a rectangular room. Add the length and width, multiply the result by two, and then by the height:
Gross wall surface area = 2 × (length + width) × height
This formula works if all the walls have the same height. When there is a sloped ceiling, a partial wall, or an open space, divide the room into simple rectangles and calculate each one separately.
How to measure irregular walls
Do not try to obtain the entire irregular surface with a single operation. Draw a basic diagram of the wall, separate it into rectangles, and calculate each part. Then add the results.
For example, a recess can add two narrow panels that do not appear when measuring only the overall length of the room. The opposite can also happen: a floor-to-ceiling built-in wardrobe occupies an area that you will not paint. Write down these decisions on the sketch so as not to add a surface twice or forget a visible side.
Measure up to the actual point where the color will end. If a wall is to be painted up to a molding, use that height. If the color continues above, include the entire corresponding surface.
How to calculate the paint for the ceiling
The ceiling is calculated by multiplying the length of the room by the width. In a room measuring 3.60 m by 3 m, the ceiling measures 10.80 m².
Calculate the ceiling separately even if it is going to receive the same color as the walls. This way you can clearly see what part of the purchase corresponds to each surface and decide if the available quantity covers the entire job.
If the ceiling and walls are in different colors, do not add their areas before converting them into liters. Make a calculation for each color. The leftover paint of one shade does not compensate for the lack of another.
How to subtract doors and windows when calculating paint
Subtracting all the openings produces a more precise figure, but also reduces the margin. In a room with a standard door and window, you can measure them and deduct them precisely or keep part of that surface in the calculation to cover touch-ups.
To subtract a door, multiply its width by its height. Repeat the operation with the window and deduct both surfaces from the gross total of walls.
You must maintain a consistent criterion. If you are not going to paint the inside of the window opening or the sides of a deep door, deduct the entire opening. If you are going to paint jambs, lintels, or other returns, those small surfaces are still part of the job.
When the result is close to the limit of a size, round up. Saving a small amount over the calculation may force you to interrupt the second coat, and a new mixture applied at another time can make it difficult for the finish to be uniform.
It is also not worth deducting outlets, switches, or small holes. The time spent measuring them does not provide a practical difference for the purchase and eliminates part of the planned margin.
Example: how much paint do I need for a room of 3.60 × 3 m
We are going to calculate a rectangular room 3.60 m long, 3 m wide, and 2.50 m high. It has a door measuring 0.80 × 2 m and a window measuring 1.20 × 1.20 m. This is a calculation example, not a standard room measurement.
| Surface | Operation | Resulting area | Paint at 5 m²/L |
|---|---|---|---|
| Two long walls | 3.60 × 2.50 × 2 | 18 m² | 3.60 L |
| Two short walls | 3 × 2.50 × 2 | 15 m² | 3 L |
| Gross total of walls | 18 + 15 | 33 m² | 6.60 L |
| Door | 0.80 × 2 | 1.60 m² | 0.32 L |
| Window | 1.20 × 1.20 | 1.44 m² | 0.29 L |
| Approximate net wall | 33 - 1.60 - 1.44 | 29.96 m² | 5.99 L |
| Ceiling, if painted | 3.60 × 3 | 10.80 m² | 2.16 L |
The walls add up to practically 30 m² once the door and window are deducted. By dividing 30 by 5, the result is 6 L to apply two coats with a margin.
If all the walls are the same color, those 6 L can be organized with the available sizes. One option is to combine 4 L with 2 L. If you already have a roller, brush, tray, tape, and plastic, you can check the mineral paint in different sizes and the 2 L paint bag.
The ceiling requires another calculation. Its 10.80 m² are divided by 5, which gives 2.16 L. Since the calculated quantity exceeds 2 L, it is not advisable to treat it as a surface of 10 m² or rely on the most optimistic coverage. Round up to the larger size that allows you to complete the two coats.
If the ceiling and walls have the same shade, you can add their surfaces before dividing: 29.96 + 10.80 = 40.76 m². That surface requires a little over 8 L according to the reference of 5 m² per liter. The final choice must cover the full result, not fall short.
How to calculate how much paint to buy when there are several colors
An accent wall changes the way you buy even if it does not change the total square meters. Suppose that in the previous example one long wall will have one color and the other three, another. You must separate the 9 m² of that wall before subtracting the corresponding openings.
First calculate the exact surface area of the minority color. Then calculate the rest. Divide each figure by 5 and round each color independently.
This method may leave more leftover paint than buying a single color, because each shade must reach the necessary size on its own. This is the practical cost of dividing a room into several colors. Do not reduce the two quantities thinking you can exchange the leftover.
Test the color on the wall before ordering all the liters. Lighting, orientation, and the elements already in the room change how it is perceived. The 100 ml paint sample allows you to apply the shade to the real surface, and this guide explains how to test paint samples on the wall.
All the colors in the PaintUber catalog have the same price, without a surcharge for choosing a specific shade. Even so, it is advisable to confirm the color before calculating and buying each size, especially if you are going to combine several walls.
Common errors when calculating paint per square meter
The most frequent error is measuring the floor and using that figure as the wall surface. The length and width of the room help calculate the perimeter, but you need to multiply by the height.
Another mistake is reading “10-12 m² per liter and coat” and buying one liter for every 10 or 12 m² of finished work. That calculation only covers one coat. For two coats with a margin, use 5 m² per liter.
It is also usually rounded down. If the calculation gives something more than an available size, buy the next size or combine containers until you exceed the required quantity. The calculation does not guarantee that you can empty the container to the last drop on the wall.
Subtracting too much is another cause of material shortage. Deducting every outlet, baseboard, or small element gives a false sense of precision. Keep that margin for the roller, the tray, and the touch-ups.
Measuring the entire room as if it were a single color also produces errors. Separate walls, ceiling, and colors before converting square meters into liters.
Finally, do not confuse a wall pending repair with a wall ready to paint. If there are loose areas, chipped areas, or an unresolved cause of moisture, the measured surface may be correct, but the work is not yet prepared to receive paint.
How to calculate and buy paint with PaintUber
The process within PaintUber follows the same order as the manual calculation. First, you enter or check the square meters of wall. Use the actual measurement of each panel and work with the surface that will receive the same color.
Then you choose the shade. If you are still not sure, ask for a 100 ml sample beforehand and test it on the wall. Leave the sample in its real location to observe it next to the floor, the furniture, and the light of the room.
With the meters and the color decided, you select the size. For the purchase calculation, the reference of 5 m² per liter is maintained: 2 L for about 10 m² of wall and 4 L for about 20 m². Those who already have tools can choose loose paint for interiors. Those who need to start with everything can choose the kit.
The kit brings together the paint and the necessary tools to paint: 22 cm roller with handle, flat brush, tray, 3.74 × 3.74 m plastic drop cloth, and 45 mm painter's tape. This avoids calculating the liters on one side and preparing a second purchase of tools later.
After the order, delivery is made in 24-72 hours. After the purchase, the guide “How to paint your house in a weekend” is sent by email. PaintUber sells directly to the individual and does not offer an application service, so the measurement and the work are carried out by the person who lives in the house.
The paint is manufactured by Naturmatt Smart Materials, S.L., while PaintUber, whose selling company is Aleph Zero, S.L.U., sells it to the final customer. The plant where it is manufactured is ISO 9001 and ISO 14001 certified.
It is a mineral paint on an aqueous base with a load of calcium carbonate CACO3®. It is breathable, allows water vapor from the wall to pass through, has zero yellowing, is very washable, and does not crack. Its drying time is 1 hour to the touch, 2 to 4 hours between coats, and 24 hours in total.
According to the container label, it contains less than 1 g/L of VOC. The European legal limit for a water-based interior matte is 30 g/L, within the framework set by the Directive 2004/42/EC on volatile organic compounds. Furthermore, it does not present hazard indications according to the CLP Regulation 1272/2008.
How to prepare the wall without altering the paint calculation
The amount of paint is calculated over the final surface you are going to cover, but before that you must check that the surface is firm and clean. Remove the loose parts and correct the imperfections before starting. This guide to prepare a wall before painting details the work order to achieve a uniform base.
A localized repair does not necessarily change the square meters, although it can make an area absorb differently. That is why a prudent figure of 5 m² per liter is used and rounded up.
Do not paint over an active leak, rising damp, or structural flaking expecting the paint to solve it. First, you must identify and correct the cause. Painting over it can hide the problem for a while, but it does not repair its origin. If water-related stains or peeling appear, first check how to prepare a damp wall before painting.
Protect the floor and the elements you are not going to paint before opening the container. Remove the paint, load the roller without saturating it, and spread the material evenly. Respect the 2-4 hours between coats. A coat that is too thick does not replace two coats and can use up the planned material before finishing the room.
Frequently asked questions about how much paint I need per square meter
How many square meters do I paint with one liter of paint?
To plan two coats with margin, calculate about 5 m² of surface per liter. The indicated yield is 10-12 m² per liter and coat, but you should not use that figure as full coverage of two coats.
How much paint do I need for 10 m² of wall?
Divide 10 by 5. You need 2 L to apply two coats with margin. That reference corresponds to a 2 L kit for about 10 m² of wall.
How much paint do I need for 20 m² of wall?
You need 4 L for two coats with margin. The operation is 20 ÷ 5 = 4. A 4 L kit is designed for about 20 m² of wall.
Do I have to multiply by two if I am going to give two coats?
No, as long as you use the reference of 5 m² per liter. That figure already accounts for two coats and a margin. You would only have to treat each coat separately if you were using the yield of 10-12 m² per liter and coat.
Should I subtract the doors and windows?
You can subtract them if you measure them correctly, especially when they occupy a significant part of the wall. Do not discount small elements such as outlets or switches. When the quantity is close to the limit of a format, round up.
How do I calculate the paint if the ceiling has another color?
Calculate the ceiling by multiplying length by width, divide the result by 5 and buy that color separately. Make another calculation for the walls. Do not add different colors before choosing the liters.
What do I do with the leftover paint?
Keep the container properly closed and save the color reference. A small amount can serve for future touch-ups on that same wall. Do not plan the purchase to the limit just to avoid any leftovers.
Does paint fix a damp wall?
No. A leak, rising damp, or structural peeling requires first solving the cause. Paint is the final finish and does not replace that repair.
The PaintUber paint kit brings together mineral paint, the roller, the brush, the tray, the plastic, and the tape in one box. Measure your walls, divide the square meters by 5 and choose the necessary quantity to apply two coats. Read next: How much paint do I need per square meter: calculation for two coats. Read next: How much paint do I need per square meter for a room. Read next: How much paint do I need per square meter for a room. Read next: How to paint a room step by step and calculate the paint. Read next: Best colors to paint the living room according to the light and furniture.