Let's be real - nothing's worse than ordering custom blinds only to find they don't fit your window. I learned this the hard way when I botched my first measuring job and ended up with blinds that left ugly gaps on both sides. Had to eat the return shipping costs and wait another three weeks for replacements. Total nightmare.
That's why getting your measurements right is crucial before ordering. Whether you're doing inside mount or outside mount, the process is simpler than you think if you follow some basic rules. I'll walk you through everything from tools to common pitfalls, based on helping over 200 homeowners get their window treatments right.
Why Measuring Right Matters So Much
If your measurements are off by even 1/8", you might end up with blinds that won't install properly. Too wide and they won't fit the bracket. Too narrow and you'll see light gaps. Either way, you're stuck with return hassles or living with a bad installation.
Here's what happens when measurements go wrong:
- Blinds rub against window frames causing operation issues
- Light leaks around edges defeat the purpose of light control
- Improper support creates safety hazards (especially with heavy blinds)
- Manufacturer warranties get voided by incorrect measurements
Pro Tip: Measure twice, order once. I always take three measurements at different points because windows and frames are rarely perfectly square. That extra minute saves weeks of frustration.
Gathering Your Measuring Toolkit
You don't need fancy equipment, but these basics will help:
- Steel measuring tape - Avoid fabric tapes that stretch (trust me, I made this mistake in my first apartment)
- Pencil and paper - Digital notes work too
- Step ladder for high windows
- Level (optional but helpful for checking square)
- Flashlight to see recesses clearly
Don't use a ruler or yardstick - they're too inflexible for window recesses. And seriously, writing down measurements beats trusting your memory. I once mixed up two windows and ended up with a 24" blind in a 36" opening. Not my finest moment.
Inside Mount vs Outside Mount: What's the Difference?
| Feature | Inside Mount | Outside Mount |
|---|---|---|
| Installation Location | Inside window recess | On wall/molding around window |
| Window Depth Needed | Min. 2.5" depth required | No depth requirements |
| Light Control | Possible light gaps | Complete coverage |
| Appearance | Sleek, built-in look | Makes window appear larger |
| Best For | Deep window wells | Shallow windows or irregular openings |
Personal opinion? I prefer inside mount for modern homes because it looks cleaner. But in my 1920s bungalow with uneven frames, outside mount saved my sanity. Neither is "better" - just different solutions.
How to Measure for Inside Mount Blinds
Step 1: Measure Width
Measure at three points: top, middle, and bottom of the window recess. Write down the narrowest measurement to the nearest 1/8". That's your ordering width.
Why the narrowest? Because manufacturers will deduct 1/4" to 1/2" for mounting brackets. If you give them the widest measurement, your blinds will be too small after deductions.
Step 2: Measure Height
Measure from the top of the recess to the sill at left, center, and right. Use the longest measurement for your ordering height. Unlike width, you don't want deductions here.
Step 3: Check Depth
This step gets overlooked! Measure from the front of the recess to the glass. Most blinds need at least 2.5" depth. Cellular shades might need 3-4". If your depth is insufficient, outside mount is your solution.
Watch Out: Don't assume all windows in the same room are identical. In my living room, three "same size" windows varied by 5/8". Measure each opening separately!
How to Measure for Outside Mount Blinds
Step 1: Decide Coverage Area
How much overlap do you want? I recommend at least 1.5" per side for light blocking. Mark your desired coverage points lightly with pencil.
Step 2: Measure Width
Measure between your marks at top, middle, and bottom. Use the widest measurement for ordering width. No deductions needed since brackets mount outside the measurement area.
Step 3: Measure Height
Measure from above your top mark to below your bottom mark at both sides. Use the longest measurement for ordering height. Want a floor-to-ceiling look? Measure full height from ceiling.
Step 4: Check Obstructions
Scan for outlet covers, light switches, or trim that might interfere with installation. I once installed blinds that covered a thermostat - rookie mistake.
Measuring Challenges for Different Window Types
Not all windows play nice. Here's how I handle special situations:
Bay and Bow Windows
These require individual measurements for each window section. Measure width and height separately for each angled panel. Crucial: note the exact angles where panels meet. Protractors help, but many manufacturers provide angle templates.
French Doors and Patio Doors
For doors that open inward, inside mount requires precise clearance measurements. Measure from glass to door handle. For sliding doors, track systems often need specialized mounting.
Arched Windows
Best left to professionals in my opinion. But if DIY-ing, measure the straight portion below the arch separately from the curved section. Many companies make blinds only for the lower rectangle.
Top 5 Measuring Mistakes I've Seen (And How to Avoid Them)
- Measuring only once - Windows shift in houses. Always measure at three points.
- Including trim in inside mount measurements - Measure only the recess space between frames.
- Forgetting depth checks - That beautiful blind won't fit if the recess is too shallow.
- Confusing width and height - Label clearly: Width always comes first in orders.
- Ignoring obstructions - Window cranks and locks can block blind operation.
| Mistake | Consequence | Fix |
|---|---|---|
| Measuring frame instead of recess | Blinds too small | Measure within the recess |
| Using longest width measurement | Blinds won't fit brackets | Always use narrowest width |
| Measuring after removing old blinds | Inaccurate measurements | Measure before removal |
| Not checking for square | Gaps at top or bottom | Measure both sides |
| Measuring over window treatments | Inaccurate readings | Remove existing blinds first |
FAQ: Your Measuring Questions Answered
Should I measure in inches or centimeters?
Most US manufacturers work in inches to 1/8" increments. I recommend inches even if you normally use metric - conversions create rounding errors.
How precise do measurements need to be?
Down to 1/8". If your tape only has 1/4" marks, round down for width measurements. For example, record 28 3/8" not 28 1/2".
Do I need professional measuring services?
For standard windows? Probably not. But for complex installations like arched windows or entire homes, $100-$150 for pro measuring saves money on costly mistakes.
What if my measurements are between sizes?
Manufacturers typically round down for width (to ensure fit) and up for height. Provide exact measurements and they'll adjust.
How long does measuring take?
For a typical room with 3 windows? About 15 minutes once you know what you're doing. My first time took nearly an hour though!
Can I measure without removing existing blinds?
Absolutely not. Existing hardware affects measurements. Plus you need to see the actual frame condition.
What about tilt direction clearance?
Critical for inside mount! Ensure at least 1.5" clearance depth for wand operation or 2" for cordless tilt.
After Measuring: Ordering Your Blinds
When placing your order:
- Specify clearly whether measurements are for inside or outside mount
- Confirm deduction policies (many companies auto-deduct 1/4" for brackets)
- Provide exact measurements - don't round yourself
- Note any special requirements like extra clearance for handles
Good companies will double-check measurements that seem unusual. When I ordered blinds for my angled attic windows, the rep called to confirm the measurements before cutting. That's quality service.
Final Reality Check
Even with perfect measurements, installation can present surprises. Old houses settle, walls aren't plumb, and window frames warp. That's why I keep painter's caulk handy to fill small gaps and always check brackets with a level before drilling.
Remember that how you measure for blinds determines 90% of installation success. Take your time, follow these steps, and you'll avoid the frustration I experienced with my first botched order. Accurate measurements mean blinds that fit perfectly, operate smoothly, and look professionally installed.
Got walls that aren't square? My contractor friend taught me this trick: Install the brackets slightly angled to match the window slope. The blinds will hang straight even if the frame isn't level. Little fixes like that make all the difference between good and great results.
Still feeling unsure? Many manufacturers offer free video consultations where you can show them your windows in real time. Worth considering before making expensive custom orders. Happy measuring!
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