Height

Curtain rod/tracks are usually 4-6" above the top of the window. To make the ceiling appear higher, they should be closer to the ceiling.

Grommet

X = A + 1 1/8" (Top of the panel to top of the inner grommet ring is 1 1/8")

Rod pocket

X = (If slips over the rod) A + 0.5"

X = (If hooks into the rings, covering the rod) A

X = (If hooks into the rings, not covering the rod) B

All pleated headings

X = (If covering the rod) A

X = (If not covering the rod) B

Then, account for the floor distance (three popular looks)

Floating above the floor

Curtain height = X - 0.5"

Just hitting the floor the floor

Curtain height = X

Puddling

Curtain height = X + 2" to 6"

Width

Rod/Track width (C) is decided by the window width (D) and stack width (E)

(Rods/tracks are usually 1.3x the width of the window width.)

Grommet/Rod pocket

Curtain width (min fullness) = C x 1.5

Curtain width (recommended) = C x 2

Curtain width (max fullness) = C x 2.5

All pleated headings

Curtain width = C