Methodology

This page explains two things: how the paint calculator works and how we write the guides. That way you know what to expect from each and what not to.

Last updated: 3 November 2026.

What the calculator does

The calculator draws the room from what you type: the type of room (living room, bedroom, kitchen, bathroom or hallway), the length, width and ceiling height in metres, the number of windows and doors, the number of coats, whether you want to paint the ceiling, and the colour.

• The area to paint is a geometric calculation: the perimeter of the room times the ceiling height, minus the windows and doors, plus the ceiling if you include it. For windows we use a typical size of 1.2 × 1.2 m and for doors 0.8 × 2.0 m. If yours are very different, the area changes.
• The litres are the area times the number of coats, divided by the paint’s coverage in m² per litre. The coverage shown at first is only an example. The right value is on the data sheet of the paint you will use. The result is rounded up to the nearest half litre.
• The drawing follows the same sizes. It is a diagram to show the proportions, not a project.
• What you see on the wall (“nothing”, “damp”, “mould” or “salt”) is there so that the request says what is wrong. It is not a diagnosis.
• The calculator shows no prices. We will only do so when we can justify the values with a dated source.

What the calculator does not know

Many things decide the work and the paint and do not pass through a form:

• the real state of the walls: cracks, peeling paint, loose plaster;
• where the damp comes from (condensation, damp rising from the ground, or water coming in from outside or from the flat above), which can only be worked out on site;
• whether the wall is very absorbent, whether it needs a primer, or whether the new colour is very different from the old one;
• furniture, skirting boards, high ceilings and access;
• VAT and the conditions of the work.

Painting over mould or salt without treating the cause does not solve the problem. Use the calculator to organise the description and always ask for a visit and a written quote.

What happens to what you type

What you describe in the calculator stays only in the page open in your browser until you send something. When you send the form, we store the description together with your name, phone number and town. Details are in the Privacy policy.

How we write the guides

1. We start from a real question from someone with a wall to paint or a damp wall: how much paint to buy, where the stain comes from, who pays when the water comes from the flat above.

2. We look for sources. We prefer these:

   • the Diário da República and the Civil Code, on dre.pt;
   • LNEC publications on damp in buildings;
   • DGS and SNS 24, on mould indoors and health;
   • ADENE, on ventilation and energy certificates;
   • IMPIC, on who may do building work;
   • municipal councils;
   • paint data sheets, with the date we read them.

   Price websites and forums are only an indication, never proof.

3. We write in European Portuguese, in plain words. We explain each technical term the first time it appears.

4. We cite the sources and the date we read them. Each guide says which sources it used.

5. We give no prices without a source. When we talk about cost, we explain what pushes it up or down. We only give values if they come from a source we name, with the date we checked.

6. We say what we could not confirm. If we found no reliable source, the text says it depends and what to ask whoever does the work, instead of stating.

The role of artificial intelligence

We use artificial intelligence tools to help research, organise and draft, and to generate the illustrations that go with the guides. Generated pictures are labelled “Illustration”. What goes on the site is checked against the sources we cite. We do not claim the guides were reviewed by an engineer, an architect or a doctor. They are general information, written with care, and do not replace the opinion of a specialist or a visit to your home.

Independence and limits

• We do not do painting or building work. We do not recommend paint brands or companies in the guides.
• At the moment we do not forward requests to painters. If that changes, we will say so here and in the Privacy policy, and ask for new consent.
• Rules change. When we talk about legislation, we give the date we read the source. Always check the official site before deciding.

How to ask for a correction

Did you find an error, outdated information or a sentence that is unclear? Write to [email protected] with the page address and what is wrong. If the error is ours, we correct it and update the page.