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Flat Area Calculator
Here's a picture of a rectangle (tan) plus a triangle (green.) Your home walls and deck will be comprised of shapes similar to these. With no intent to insult anyone's intelligence, we've simply called dimensions "height", "width", and "length" to keep them identified and to avoid using technical or mathematical terms. You'll need paper and pencil to write down the sizes (dimensions) of these areas.

Every time your house wall changes direction, there is a new wall section as shown at left. Some will have triangular gable areas (green), and some will be plain rectangles (tan.)
Decks may have triangles and rectangles, as well as circles.
Find all of these areas on your house, and write down the dimensions in feet and the type of area for each. Use a tape marked in feet + inches, and convert inches to decimal feet per the conversion table (below left.) Here's a worksheet you can print, if you wish.
The calculators below will compute areas for you, and the amount of flat surface you need to cover.

Area is calculated by multiplying feet in width by feet in length (ft x ft) to get square feet (ft².) The calculators below will do the math for you, including the formulas for areas of triangles and circles. For each surface area you measured, enter the appropriate values in the calculator(s), then write the result on your worksheet. When all areas have been calculated, add them all up to get the total square feet to be finished.

The conversion table (below left) show conversion from inches to decimal feet. For instance, if you measure 6 feet and 2 inches (same as 6'-2"), the value in feet is 6 + .17, or 6.17 (same as 6.17')

Note: After entering a value, click outside the entry box to initiate the calculation. Circles on your structure may be only half or quarter-circles, but all will have a diameter. Enter the diameter of a circle in feet at right to find the areas for 1/4, 1/2, 3/4 and full sections. Write the appropriate section answer(s) on your worksheet.

conversions

inches

feet

1

.08

2

.17

3

.25

4

.33

5

.42

6

.50

7

.58

8

.67

9

.75

10

.83

11

.92

ENTER DIAMETER

AREA
1/4 = ft²
1/2 = ft²
3/4 = ft²
full = ft²

In the calculator below, the "Triangle + Rectangle", calculates the entire area of a gabled house end, e.g., the sum of the tan and green areas. Enter all dimensions in feet.

Rectangle: Enter Width & Length
Triangle: Enter Length & Height
Triangle + Rectangle: Enter all three

WIDTH
LENGTH
HEIGHT

CALCULATED AREA:
= ft²

Write the answers for each calculation on your worksheet.

Checkpoints:
As you tally your results, make a "good sense" comparison as follows:

A 20' x 30' deck is 600 ft²
The area of the siding on a house will be roughly equal to its floor space (±10%). For instance,
a one story, 30' x 60' house (about 1800 ft²) will have about 1600 to 2000 ft² of exterior siding
If your numbers seem vastly out of line, then recheck your written measurements! Also see the Roof Area Calculator

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