01
Inside mount: measure the usable opening
Measure width at top, middle, and bottom and height at left, center, and right using a rigid tape. Record the values exactly and note whether the opening is out of square. Verify flat depth for brackets, fascia, handles, cranks, screens, and tilt-in window movement. Product instructions determine deductions.
02
Outside mount: design the coverage
Choose where hardware can anchor and how far the treatment should overlap the opening for privacy, light control, and proportion. Check trim projection, wall condition, ceiling, adjacent corners, crown molding, and the space needed for the roll, stack, or valance.
03
Doors and specialty glass need more information
French doors require handle and lever clearance, hold-down planning, and consideration of door swing. Sliding doors require active-panel and stack planning. Arches, angles, skylights, and deep or shallow frames may require templates or product-specific methods.
04
Know when the order deserves field verification
Large and motorized shades involve tube size, alignment, power, access, and control coordination. Custom fabric cannot simply be returned to a shelf if dimensions are wrong. Professional measurement transfers the opening from a rough number into an installable specification.
Decision table
Compare the practical tradeoffs.
| Condition | Record | Why it matters |
|---|---|---|
| Inside mount | Three widths, three heights, depth | Reveals variation and bracket room |
| Outside mount | Finished coverage and mounting surface | Controls overlap and proportion |
| Door | Glass, handle, hinge, swing, hold-down needs | Prevents hardware conflicts |
| Large/motorized | Span, level, structure, power, access | Coordinates engineering and service |
| Specialty shape | Geometry, template needs, operation | Determines feasibility |
Measure to understand the opening; use professional field measurement to commit a custom ordered system.