Curtain Length Calculator
Find the exact curtain drop for sill, apron, floor and puddle length hangings.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Measure both the window sill and the top of the window from the floor. The rod sits above the window top; panel drop is measured from the rod to the selected hem position. Confirm the finished drop with the curtain maker.
Worked example
calculated with the default values below
Distance floor to window top 84 in · Distance floor to window sill 36 in · Rod height above window top 4 in · Hanging style Floor length Rod top from floor 88.0 in · Panel length to order 87.5 in · Panel length to order 222.3 cm
General background references
Disclaimer
These calculators provide planning estimates only. Building codes, wiring regulations and safety requirements differ by country and change over time, and nothing here replaces a licensed professional or a permit. For structural, electrical or gas work, follow local code and have the installation inspected.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
rodTop = windowTop + rodHeight; panelLength = rodTop − hemHeight
- S
- Sill height from floor
- r
- Rod height above window top
- T
- Window top height from floor
Rod top = window top + rod rise. Hem targets: sill S, 4 in below S−4, apron S−8, floor 0.5 in above floor, break 1 in below floor, puddle 4 in below floor. Panel length = rod top − target height; cm = in × 2.54.
Frequently asked questions
Why does the puddle hanging style add extra curtain length?
The rod top is the window-top height plus the rod rise. Panel length runs from that point to the target hem: the sill, 4 or 8 inches below it, or the floor with the selected break/puddle allowance. With defaults, the rod top is 88 inches and the sill is 36 inches, so sill-length panels are 52 inches.