How to Measure Your Walls for Painting (Without Making Mistakes)

Getting your wall measurements right is the first step to a successful painting project. Here's a simple, step-by-step guide to measuring your walls accurately so you buy the right amount of paint.

7/13/20262 min read

Measuring your walls before you buy paint seems straightforward, but it's one of the most common areas where people go wrong. Inaccurate measurements lead to either running out of paint mid-job or ending up with far more than you need. Here's how to do it properly.

What You'll Need

A tape measure (5 metres or longer is ideal)

A notepad and pen or your phone to record measurements

A calculator (or use our paint calculator)

Step 1: Measure the Perimeter for Walls

The perimeter is the total distance around the room. To find it:

1. Measure the length of each wall in metres.

2. Add all the wall lengths together.

Example: A room with two walls of 4 metres and two walls of 3 metres has a perimeter of 14 metres.

Tip: Measure at skirting board height where the room is widest. Alcoves and chimney breasts can be tricky — measure each surface individually and add them together.

Step 2: Measure the Ceiling Height

Stand close to a wall and measure from floor to ceiling. In most UK homes this is between 2.3 and 2.7 metres. Record this figure.

Step 3: Calculate Total Wall Area

Multiply the perimeter by the ceiling height:

Total wall area = perimeter x ceiling height

Using the example above: 14 x 2.4 = 33.6 square metres.

Step 4: Subtract Doors and Windows

You don't need to paint doors and windows, so subtract their area:

A standard UK door is approximately 2.0 x 0.75 metres = 1.5 sq m

A standard window is approximately 1.2 x 1.0 metres = 1.2 sq m

Subtract the total door and window area from your wall area.

Step 5: Measure the Ceiling (If Painting)

For the ceiling, measure the room length and room width, then multiply:

Ceiling area = room length x room width

Example: A 4m x 5m room has a ceiling area of 20 square metres.

Common Measuring Mistakes to Avoid

Forgetting to account for multiple coats: Always multiply your area by the number of coats before calculating litres needed.

Measuring only one wall and multiplying: This only works if all walls are exactly the same size, which is rarely the case.

Not accounting for irregular rooms: L-shaped rooms should be split into rectangles and measured separately.

Once You Have Your Measurements

Once you've noted your total area and decided how many coats you'll apply, enter everything into our free UK Paint Calculator for an instant, accurate estimate of how many litres you need to buy.