Curtain Length Calculator Formula

Understand the math behind the curtain length calculator. Each variable explained with a worked example.

Use the Curtain Length Calculator

Formulas Used

Panel Length Needed

panel_length = window_height + mount_above + extra_length

Curtain Rod Width

rod_width = window_width + 12

Total Fabric Width (2x fullness)

total_fabric_width = window_width * 2

Variables

VariableDescriptionDefault
window_widthWindow Width(in)48
window_heightWindow Top to Sill(in)60
mount_aboveMount Above Window(in)4
hang_styleHang Style1
extra_lengthDerived value= hang_style == 1 ? 0 : (hang_style == 2 ? 4 : 24)calculated

How It Works

How to Measure Curtains

Curtain length depends on window height, how high above the window you mount the rod, and the desired hanging style.

Formula

Panel Length = Window Height + Mount Above + Style Extra

Rod Width = Window Width + 6 inches on each side (12 total)

For fullness, total fabric width should be 2-2.5 times the window width.

Worked Example

48-inch wide window, 60-inch to sill, rod mounted 4 inches above, floor-length curtains.

window_width = 48window_height = 60mount_above = 4hang_style = 3
  1. 01Panel length = 60 + 4 + 24 = 88 inches
  2. 02Rod width = 48 + 12 = 60 inches
  3. 03Total fabric width = 48 x 2 = 96 inches

Ready to run the numbers?

Open Curtain Length Calculator