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Fiber Cement Siding Calculator

Siding Exposure Lap

A simple fiber cement siding calculator that will calculate the amount of boards needed to cover a wall. It can be used for any type of siding that comes in boards of one length.


Siding length, siding width and exposure need to be entered in decimal inches.

Most commonly used board is 12' x 8 ¼" with an exposure of 7"
Values that need to be entered for this size board would be:
Siding Length: 144"
Siding Width:  8.25
Exposure:  7
Fraction to Decimal Conversion Chart
1/8     0.125
1/4     0.25
3/8     0.375
1/2     0.5
5/8     0.625
3/4     0.75
7/8     0.875

After entering these three values you have to add a wall section. In the wall section you will add the wall length and the height of the wall.

The values entered in the first three fields plus the two in the wall section will provide you with a Total amount needed:

  1. For number of planks
  2. Trim to cover both ends of the wall.
  3. Total Wrap (the square footage of the wall for the house wrap or paper. If the wall is higher than the length of the wrap you are using you will have to add some for the required overlap.)
  4. 4 A nail count based on nailing the siding at 2' centers

If there are window and/or door openings in your wall, you can add these next. Click "Add Window" or "Add Door" and enter the sizes. The total amount of siding needed will be reduced as well as the nail count and house wrap needed when these items are calculated.

If you did not enter a trim width in the first section it will include a trim based on the values you entered for the sizes of the window(s) and door(s). You can add the trim width at this time but you will have to hit the calculate button for window(s) and door(s) again and it will calculate trim needed based on your selection of trim needed including the width of the trim.

The same goes for the Barge board entry in the first section. If you add the value here after the wall values have been calculated you will have to calculate one more time with a value for Barge board entered. It will give you a running total of Barge boards needed plus the required drip cap. At the same time it will reduce the amount of siding needed.

  • Note:
  • Siding needed does not include a waste factor.

All Amounts must be Entered

Siding Length:   inch
Siding Width:   inch
Exposure:   inch

Total amount needed:

Total Siding    # of Boards
Total Wall Area: ft ²

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