When you’re ready to replace your home’s siding, you’ll need to take quite a few different measurements. Anyone who can read a tape measure can estimate material needs for siding, J-channel trim, starter strips, undersill trim, and corner trim. Aside from plenty of work with the measuring tape, learning how to calculate siding is very straightforward.

How to Calculate Siding Directions

1. On your paper, list each wall, door, and window so that you don’t miss any places.
   1. A rudimentary sketch of your home will be helpful for keeping track of everything.
2. To estimate for siding, measure the length and width of each wall one at a time.
3. As you get the length and width measurements for each wall, write them on your list.
4. Once you have all wall dimensions, go through your list and multiply length by width on each wall.
   1. These calculations give you the square footage of surface area for each wall.
5. Add the square footage numbers for all walls to obtain the total siding square footage.
6. Divide the total square footage number by 100 because siding is sold in 100-square-foot units.
   1. The resulting figure tells you how many units of siding to buy.
7. To estimate how much J-channel trim is needed, measure the edges of doors and windows and top length of each wall.
8. Add these measurements and write down the total on your list for J-channel trim.
9. Next, measure the bottom length of each wall to estimate for starter strips.
10. Add all bottom wall measurements and write down the total for starter strips.
11. Undersill trim, also known as utility trim, covers the exposed top edges of vinyl siding.
    1. Measure along the walls where they meet the soffit and the widths of window sills.
    2. Add the figures for all walls and windows and write the total on your list for undersill trim.
12. For corner trim, measure the vertical lengths of all outside and inside corners.
13. Add the corner measurements and write the total on your list for corner trim.