Flat Area Calculator determines area of siding, walls & decks         Also see the Roof 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.)
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 calculaton.

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
  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.
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:
Triangle:
Triangle + Rectangle: 		Enter Width & Length.
Enter Length & Height.
Enter all three!
WIDTH
LENGTH
HEIGHT
CALCULATED AREA:
= ft2
Write the answers for each calculation on a worksheet.

Checkpoints:
As you tally your results, make a "good sense" comparison as follows:
• A 20ft x 30ft 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 60ft house (about 1800 ft2) will have about 1600-2000 ft2 of exterior siding.
If your numbers seem vastly out of line, then recheck your written measurements!

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