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Getting accurate measurements is the difference between blinds that fit perfectly and ones that gap, bind, or cannot be installed at all. This guide from Sun Stoppers Window Tinting in Charlotte walks you through the exact steps for how to measure for blinds, covering inside mounts, outside mounts, bay windows, squareness checks, manufacturer deductions, and how to record everything correctly for ordering.
To measure blinds with precision, you need a steel tape measure, marking tools, and basic leveling equipment.
| Tool | Purpose |
|---|---|
| Steel tape measure (25 ft recommended) | 1/8 inch precision, essential for accuracy |
| Pencil and notepad | Record measurements for each window |
| Step stool or ladder | Access higher windows safely |
| Small level | Check frame alignment and squareness |
| Masking tape | Mark measurement points on the frame |
| Smartphone or camera | Document window openings and obstructions |
| Cardboard template | Simulate headrail depth before ordering |
The cardboard template is especially useful for bay windows and angled configurations where headrail clearance must be confirmed before placing an order.
For inside mounts, measure width and height at three points and use the smallest width and largest height.
Measure the width at the top, middle, and bottom of the window opening. Record each value to the nearest 1/8 inch. Use the smallest measurement for ordering.
Example:
Measure the height on the left side, center, and right side of the window opening. Use the largest measurement for ordering.
This method accounts for uneven window frames, which are common in older homes where frames may have shifted or settled over time.
Note: Always measure the window opening itself, not the existing blind or shade, for accurate results.
Most inside mount blinds require approximately 2 to 3 inches (5 to 7.5 cm) of depth from the glass surface to the front edge of the frame, but actual requirements vary by product type and headrail design. Always check the manufacturer’s specifications before ordering.
| Mount Type | Depth Required |
|---|---|
| Standard inside mount | 2 to 3 inches |
| Slim profile blinds | 3/4 inch (approx. 2 cm); the headrail protrudes partially outside the frame |
| Flush mount (headrail fully inside frame) | Full headrail depth |
A flush mount means the headrail sits completely inside the window frame without protruding into the room, which requires the greatest depth of any mounting option. If your window frame doesn’t provide enough depth for this type of installation, switching to an outside mount is the most practical alternative.
For outside mounts, measure the full width of the area you want covered, not just the window opening, and add overlap on each side.
Example: 36″ window opening; order approximately 40 to 42″ width for standard coverage, or 42 to 48″ for blackout applications requiring maximum light control.
Larger overlaps (3+ inches per side) are recommended for:
Ensure there is sufficient flat wall space for bracket installation on both sides before ordering an outside mount.
For bay windows, treat each panel as a separate window and measure independently using the three-point method.
Testing headrail clearance with a cardboard template is critical for bay windows. Without this step, headrails can collide at corners after installation, requiring costly returns and remeasuring.
Measure diagonally from corner to corner in both directions. If the two diagonal measurements differ by more than 1/4 inch (approx. 6 mm), the window is not square.
Even if your frame has sufficient depth, obstructions can prevent inside-mount installation:
Photograph any obstructions and note their position before ordering. Some obstructions can be worked around with the right headrail design; others require switching to an outside mount.
Manufacturers apply deductions to inside mount blinds to ensure smooth operation without binding against the frame.
| Blind Type | Typical Deduction |
|---|---|
| Standard inside mount | 1/8 to 1/2 inch from the width |
| Vertical blinds | Often require approximately 1/2 inch from the height |
| Roller shades | Fabric deduction varies by brand |
Deductions vary by manufacturer and product line. Always confirm before submitting your order.
Always submit measurements in Width x Height format. This is the industry standard for blind and shade ordering.
W x H = 35 7/8″ x 58 1/4″
Clear labeling prevents ordering mistakes, speeds up production, and ensures the right blind goes to the right window during installation.
Different blind types have specific measurement requirements beyond the standard three-point method.
| Blind Type | Key Measurement Consideration |
|---|---|
| Blackout blinds | Require a larger outside mount overlap to eliminate light gaps |
| Roller shades | Include fabric deduction; confirm with the manufacturer before ordering |
| Vertical blinds | Require 1/2 inch height deduction for floor clearance |
| Cellular shades | Check the headrail depth, often deeper than standard blinds |
| Solar shades | The openness factor affects light control, privacy, and glare reduction |
Always confirm product-specific measurement requirements on the manufacturer’s spec sheet before finalizing your order.
If you’re comparing options, see our detailed guide on solar shades vs roller shades to understand the key differences in light control, privacy, and fabric design.
Even a small mistake when measuring blinds, such as choosing the wrong width point, overlooking depth requirements, or miscalculating overlap for outside mounts, can result in blinds that don’t fit properly, leave light gaps, or cannot be installed at all.
To ensure your inside or outside mount blinds are measured the first time accurately, professional on-site measuring helps eliminate guesswork, especially for bay windows, angled frames, or uneven openings.
Sun Stoppers Window Tinting in Charlotte provides precise, on-site measurement services for solar shades and blinds in Charlotte, NC, helping ensure every width, height, and depth is recorded correctly for a perfect fit.
Book your blind measurement today and avoid costly reorders.
The most common mistakes are measuring only once instead of using the three-point method, ignoring depth requirements for inside mounts, and submitting the largest width instead of the smallest for inside mounts. A steel tape measure and the three-point method eliminate most of these errors.
If the diagonal measurements differ by more than 1/4 inch (approximately 6 mm), the window is not square. An outside mount is usually the better option; it hides uneven edges and ensures smooth operation without binding.
No. Cloth tape measures stretch over time and produce inaccurate readings. Always use a steel tape measure for precision to the nearest 1/8 inch.
Submit the smallest width and the largest height from your three-point measurements. This ensures the blind will fit inside the window frame without binding against uneven edges.
Add 2-3 inches per side, 4-6 inches total, for standard coverage. For blackout blinds where light gaps are a concern, 3+ inches per side provides better coverage and privacy.
Yes. Roller shades typically include a fabric deduction to fit inside the brackets. Confirm the exact deduction with the manufacturer before ordering. Vertical blinds require approximately 1/2 inch of height deduction for floor clearance.
Cut a piece of cardboard to the same dimensions as the headrail and test-fit it inside the window frame. If it fits without contacting the glass or obstructions, the depth is sufficient for an inside mount.
Always measure the window opening, not the existing blind or shade. Existing blinds may have been ordered incorrectly or may be a different mount type than what you’re ordering.
For straightforward rectangular windows with sufficient depth and no obstructions, careful DIY measurement using the three-point method is usually sufficient. For bay windows, angled frames, uneven openings, or any configuration where you’re unsure of the mount type, professional measurement eliminates costly ordering mistakes.