Curtain Length Calculator Formula
Understand the math behind the curtain length calculator. Each variable explained with a worked example.
Formulas Used
Panel Length Needed
panel_length = window_height + mount_above + extra_lengthCurtain Rod Width
rod_width = window_width + 12Total Fabric Width (2x fullness)
total_fabric_width = window_width * 2Variables
| Variable | Description | Default |
|---|---|---|
window_width | Window Width(in) | 48 |
window_height | Window Top to Sill(in) | 60 |
mount_above | Mount Above Window(in) | 4 |
hang_style | Hang Style | 1 |
extra_length | Derived 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.
- 01Panel length = 60 + 4 + 24 = 88 inches
- 02Rod width = 48 + 12 = 60 inches
- 03Total fabric width = 48 x 2 = 96 inches
Frequently Asked Questions
How high should I mount the curtain rod?
Mounting 4-6 inches above the window frame makes windows look taller. For a dramatic effect, mount the rod just below the ceiling.
What is curtain fullness?
Fullness is the ratio of total curtain width to window width. Standard fullness is 2x (double the window width). Sheer curtains look best at 2.5-3x.
Should curtains touch the floor?
For a clean look, curtains should just kiss the floor or hang 1/2 inch above. Puddling (extra length on the floor) is a formal style choice.
Ready to run the numbers?
Open Curtain Length Calculator