First, decide between an inside mount (fits inside the window frame) or an outside mount (fits on the wall around the frame). For the inside mount, measure width and height in three places with a steel tape measure. Round to the nearest ⅛ inch. Use the smallest width and the largest height. For the outside mount, measure the area you want covered, then add extra width and height so the blind overlaps the frame. Always check window depth and hardware clearance before ordering. Measuring rules can vary by window blinds type, so confirm the details on your chosen product page.
Tools You Need For Blinds Measuring
- A steel tape measure. Cloth tapes stretch over time, which reduces accuracy on wider windows.
- A pencil and notepad, or the manufacturer’s printable worksheet, to record each reading as you go.
- A stable step stool for tall or high-set windows. Keep both feet on the stool and avoid overreaching. For very tall or wide windows, ask someone to help hold the tape steady.
- A simple sketch of the window with your numbers labeled. This prevents mix-ups when measuring several windows in one session.
Before You Measure: Choose Inside or Outside Mount
Inside mount blinds sit within the window recess for a clean, built-in look. This needs enough frame depth to hold the headrail and brackets, with no interference from a crank, lock, or handle.
Outside mount blinds are mounted on the wall or trim around the window, covering the frame entirely. This works well for shallow frames, uneven recesses, or when you want a larger-looking window with better light control.
Different blinds types can have different measuring rules. Roller blinds, Roman shades, wood or faux wooden blinds, cellular shades, and vertical blinds may each need their own deductions, minimum depths, and mounting clearances. Treat the steps below as the general method, and check the exact requirements on the product page before you order.
How to Measure for Inside-Mount Blinds
Measure Width in 3 Places
Measure the width of the window opening near the top, in the middle, and near the bottom. Record each to the nearest ⅛ inch. Use the smallest number as your final width, so the blind isn’t too wide to fit inside the frame.
Measure Height in 3 Places
Measure the height on the left side, center, and right side of the frame. Start at the top of the opening and measure down to the sill, or to wherever you want the blind to end. Use the largest number as your final height, so the blind fully covers the opening.
Measure Depth
Check how much clear space is available inside the frame, front to back. Don’t count interior molding or tracks. This tells you whether the headrail, and features like a cordless lift or motorization, will actually fit. Minimum depth typically falls between 1 1⁄2 and 2 inches, but it varies by product, so treat this as a starting point rather than a fixed rule.
Check for Handles, Cranks, Trim, and Other Obstructions
Look inside the frame for anything that could block the headrail or brackets, such as a window crank, lock, or protruding trim. If you find an obstruction, an outside mount is usually the safer choice.
How to Measure for Outside-Mount Blinds
Measure the Desired Coverage Width
Measure the width of the area you want the blind to cover. Then add extra width on each side beyond the frame, commonly 2 to 3 inches per side, to reduce light gaps along the edges. Check your product’s recommended overlap, since this figure varies between manufacturers.
Measure the Desired Coverage Height
Decide where you want the top of the blind to sit, usually 2 to 4 inches above the frame, to leave room for the mounting bracket and headrail. Measure down from that point to where you want the blind to end, at the sill, or a few inches past it for fuller coverage.
Check Wall Space and Hardware Clearance
An outside mount is generally more forgiving than an inside mount, but the wall still needs a quick check. Look for uneven surfaces, trim that sits proud of the wall, or nearby obstacles that could interfere with the brackets, especially on wider windows or walls with decorative molding.
Inside Mount vs Outside Mount: Quick Comparison
| Inside Mount | Outside Mount | |
| Where you measure | Inside the window frame opening | The wall or trim area around the frame |
| Width rule | Use the smallest of 3 readings | Add coverage on each side of the opening |
| Height rule | Use the largest of 3 readings | Measure down from your chosen top point |
| Depth requirement | Frame must clear the product’s minimum depth | Not applicable |
| Best for | Windows with enough frame depth and no obstructions | Shallow frames, uneven recesses, maximum light control |
| Light gaps | Small gaps at the sides or top are normal | Minimal, when sized with enough overlap |
How to Measure Difficult or Unusual Windows
Bay Windows
Bay windows have multiple angled panels, so measure and order each panel separately. Record each section’s width and height on its own, and note the angle where the panels meet, some products need angle-specific hardware.
French Doors and Sliding Doors
Check for handle clearance first. A protruding handle usually rules out an inside mount. An outside mount, or a product made specifically for doors, is typically the more practical choice.
Arched or Specialty Windows
Arched, circular, and other non-rectangular windows usually need a specialty product and a template-based measuring process, not the standard width-and-height method. Check the manufacturer’s dedicated guide for these shapes before you measure.
Common Measuring Mistakes
- Rounding your numbers. This is one of the most frequent causes of a poor fit. Record exact readings instead.
- Using a cloth tape measure. It can stretch, which throws off precision.
- Measuring only once. Window frames are rarely perfectly square, so one reading can miss a narrow or uneven spot.
- Skipping the depth check. This can leave you with hardware that doesn’t clear the frame on an inside mount.
- Ignoring the diagonal check. Measure the window corner to corner in both directions. If the two readings differ noticeably, the window is out of square. Follow your product’s guidance for out-of-square openings, or ask the retailer for help before ordering.
Measurement Examples
Inside-mount example: A window measures 35¾” at the top, 35⅝” in the middle, and 35½” at the bottom. The final width is 35½”, the smallest reading. Heights come in at 47¼”, 47½”, and 47⅜”. The final height is 47½”, the largest reading. Frame depth checks out at 2¼”, which clears a standard inside-mount headrail.
Outside-mount example: The window opening is 36″ wide. Adding 2½” of overlap on each side brings the final width to 41″. The blind’s top will sit 3″ above the frame and extend to 2″ below a 47″ sill height, giving a final height of roughly 52″.
Printable Blinds Measuring Checklist
| Window/Room | Mount Type | Width 1 | Width 2 | Width 3 | Final Width | Height 1 | Height 2 | Height 3 | Final Height | Depth | Obstructions | Notes |
Copy this row for each window, and keep it on hand when you place your order.
Frequently Asked Questions
Should I round my measurements up or down?
No. Record exact measurements to the nearest ⅛ inch. Manufacturers often apply their own deductions during production, but this varies by supplier, so submit your raw measurement unless told otherwise.
What’s the minimum depth needed for an inside mount?
It depends on the product, but it’s generally between 1½ and 2 inches. Check the minimum depth listed for the specific item before you order.
Do roller or Roman shades need different measurements than blinds?
Sometimes. Deductions, minimum depth, and mounting requirements can differ by product type. Use the general method in this guide as a starting point, then confirm the details for the specific shade or blind you’re buying.
What should I do if my window isn’t square?
Follow the sizing guidance for your specific product, or contact the retailer for a professional measurement rather than guessing.
How do I measure French doors or sliding doors?
Check handle clearance first. If it protrudes into the frame, an inside mount likely won’t work, measure for an outside mount, or use a product made specifically for doors.
Can I measure alone, or do I need a second person?
One person can measure most standard windows without help. For very tall or wide windows, a second person holding the tape steady makes the process easier.
