Because most walls are square or rectangular, you can determine their surface area by multiplying the width and height measurements and then subtracting any door or window space. Atypical architecture and design, however, can result in having triangular, circular or trapezoidal shapes combined with the rectangle. The key to calculating the surface area of a wall accurately is using the basic formulas for finding the area of two-dimensional shapes.

## Rectangular Walls

### Step 1

Measure the vertical height and horizontal width of the wall.

### Step 2

Multiply width and height measurements.

### Step 3

Calculate the areas for doors and windows, if any. Subtract that amount from your overall measurements to determine the actual wall surface area.

## Walls with Triangular Shapes

### Step 1

Calculate any rectangular area and write down the result.

### Step 2

Locate the triangular shape. Measure the width along its base and the height from the base to the highest point.

### Step 3

Multiply the base and height measurements then divide the result by 2. Add this to the result you recorded in Step 1.

### Step 4

Calculate the areas for doors and windows, if any. Subtract that amount from your overall measurements to determine the actual wall surface area.

## Walls with Trapezoidal Shapes

### Step 1

Calculate any rectangular area and write down the result.

### Step 2

Measure the width of the bottom, the width of the top and the height. Write these numbers down.

### Step 3

Add the width measurements together and divide by 2. Multiply this number by the height measurement. Add this result to solution in Step 1.

### Step 4

Calculate the areas for doors and windows, if any. Subtract that amount from your overall measurements to determine the actual wall surface area.

## Walls with Circular Shapes

### Step 1

Calculate any rectangular area and write down the result.

### Step 2

Measure from the middle of the circle to the edge, which is known as the radius.

### Step 3

Multiply the measurement of the radius by itself, which is also known as squaring.

### Step 4

Multiply the result of squaring the radius by 3.14.

### Step 5

Divide the result in step 4 by 2, because you most likely need the area of only a portion a circle. Add this result to the area that you calculated in Step 1.