Measuring for blinds sounds hard, but it takes about five minutes per window. You only need a steel tape measure, a pen and a notepad. Get the numbers right and your blinds fit like they belong there. Get them wrong and you pay for a second set. This CarpetHub guide walks you through every step in plain language. You will learn how to measure for inside mount, outside mount, vertical blinds and odd shaped windows. If you want a perfect fit without the guesswork, our made to measure blinds service handles the sizing for you.
How to Measure for Blinds
Measure the width in three places across your window. Measure the height in three places down your window. For inside mount, use the narrowest width and the longest height. For outside mount, add 2 to 3 inches on each side. Always write the width first and the height second. Measure to the nearest 1/8 inch and never round to the nearest half inch.
What You Need Before You Start
Grab these four things before you touch a window.
- A steel tape measure. Cloth and plastic tapes stretch and give you wrong numbers.
- A pen and paper. Never trust your memory across five windows.
- A step ladder. You need one for tall windows and accurate top readings.
- A pencil. Mark your bracket positions lightly on the wall.
Label every window as you go. Write “kitchen left” or “bedroom bay 1” on your sheet. This one habit prevents most ordering errors.
Inside Mount vs Outside Mount | Pick This First
Your mount type changes every number you write down. So decide this before you measure anything.
Inside mount sits inside the window frame or recess. It gives you a clean, built in look. Your window trim stays visible. This is the most popular choice in homes.
Outside mount sits on the wall or on the trim above your window. It covers more area and blocks more light. It also makes small windows look larger.
| Feature | Inside Mount | Outside Mount |
| Look | Neat and flush | Bold and full coverage |
| Light control | Small gaps at the sides | Best light blocking |
| Needs depth | Yes | No |
| Best for | Deep recesses and pretty trim | Shallow frames and odd windows |
| Makes window look | True size | Larger |
| Common problem | Not enough depth | Needs flat wall space |
Choose outside mount when your frame is too shallow. Choose it also when handles, cranks or locks block the recess.
Check Your Window Depth Before Anything Else
Depth is the number most people forget. It decides whether inside mount is even possible.
Measure from the front edge of your window frame back to the glass. Do this at the point where your brackets will sit. Watch out for handles, latches and cranks that stick out.
Here are the usual minimum depths for a flush inside mount fit.
| Blind Type | Approx. Minimum Depth |
| 1 inch mini blinds | 3/4 inch (19mm) |
| 2 inch faux wood blinds | 2 1/2 inches (65mm) |
| 2 inch real wood blinds | 2 inches (50mm) |
| Roller blinds | 1 1/2 to 3 inches (40 to 75mm) |
| Roman blinds | 2 to 3 1/2 inches (50 to 90mm) |
| Cellular and pleated shades | 3/4 to 1 1/2 inches (20 to 40mm) |
| Vertical blinds | 3 1/2 inches (90mm) |
| Panel track blinds | 2 to 3 1/2 inches (50 to 90mm) |
| Plantation shutters | 2 1/2 to 3 1/2 inches (65 to 90mm) |
These figures change between brands and headrail styles. Always check the depth listed on the product page before you order.
If your recess falls short, you still have options. You can choose a partial inside mount. You can also switch to outside mount and cover the frame.
How to Measure for Blinds Inside Mount
This is the method for how to measure windows for blinds inside mount. Follow all four steps.
Step 1: Measure the Width in Three Places
Measure inside the frame at the top of the window. Then measure across the middle. Then measure across the bottom.
Windows settle over time and rarely stay square. Your three numbers will often differ slightly.
Write down the narrowest of the three widths. This keeps the blind clear of the sides.
Step 2: Measure the Height in Three Places
Measure from the top of the recess to the sill on the left. Repeat in the middle. Repeat on the right.
Write down the longest of the three heights. This makes sure your blind covers the whole opening.
If your window has no sill, measure to the point where you want the blind to stop.
Step 3: Measure the Depth
Measure from the glass out to the front edge of the frame. Compare this number to the depth chart above.
Note any handle that sticks into the recess. Measure the space in front of it too.
Step 4: Check the Window is Square
Measure diagonally from the top left corner to the bottom right corner. Then measure the other diagonal.
Compare the two numbers. A difference under 1/2 inch is fine for most blinds. Shutters need a tighter tolerance of about 1/2 inch or less.
A big difference means your window leans. In that case, pick outside mount for a cleaner result.
Never Make Deductions Yourself
This trips up thousands of shoppers every year. Send the exact opening size to the maker.
The factory applies its own deduction so the blind runs freely. If you shave off half an inch first, the maker deducts again. You then end up with a gap on both sides.
How to Measure for Outside Mount Blinds
Outside mount gives you freedom. You control exactly how much area the blind covers.
Step 1: Measure the Width You Want to Cover
Measure the width of the window opening. Then add 2 to 3 inches on each side.
That overlap blocks the light gap along the edges. It also hides the brackets neatly.
For blackout blinds in a bedroom, add 3 inches or more per side.
Step 2: Measure the Height
Start where you want the top of the headrail to sit. Go at least 3 inches above the opening.
That space holds the brackets and hides the top light gap.
If your window has a sill, measure down to the sill. If you want more coverage, measure 2 to 3 inches below it. For a window with no sill, measure to the bottom of the trim or the floor level you want.
Step 3: Check the Flat Mounting Surface
You need at least 2 inches of flat wall or trim above the window. The brackets need somewhere solid to grip.
Look for pipes, alarm sensors, curtain poles and light fittings. Move your mounting point if anything blocks it.
Also check the sill sticks out less than the blind will project. If it sticks out further, ask for extension brackets.
Rounding Rules That Stop Fitting Problems
Small rounding errors cause big fitting problems. Use these simple rules.
- Measure to the nearest 1/8 inch, or the nearest millimetre in metric.
- Round the width down to the nearest 1/8 inch.
- Round the height up to the nearest 1/8 inch.
- Never round to the nearest half inch or whole inch.
- Always record as width first, then height.
Write it as W x H every time. A 36 inch by 48 inch blind is very different from a 48 inch by 36 inch blind.
How to Measure for Different Blind Types
Each blind style has its own quirks. Here is what changes.
How to Measure for Vertical Blinds
Vertical blinds usually cover wide windows and sliding doors. The vanes hang from a top track.
For inside mount, measure the width in three places and use the narrowest. Measure the height in three places and use the shortest. A short drop stops the vanes dragging on the sill.
For outside mount, add 3 to 4 inches on each side of the opening. Mount the track 3 to 4 inches above the frame.
Leave about 1/2 inch of floor clearance for floor length vanes. This keeps them swinging freely.
Also decide your stack direction now. You can stack the vanes left, right or split them in the centre.
How to Measure for Mini Blinds
Mini blinds use 1 inch slats and a slim headrail. They need very little depth.
Measure the inside width at three points and use the smallest. Measure the height at three points and use the largest.
Mini blinds fit shallow frames where wood blinds will not go. Check you have at least 3/4 inch of depth.
For outside mount mini blinds, add 1 1/2 to 2 inches per side. Their headrail is small, so the overlap can be smaller too.
How to Measure for Roller Blinds
Roller blinds need extra room for the tube and brackets. The fabric sits narrower than the total bracket width.
Measure at the very top of the recess for inside mount. That is where the brackets sit.
For outside mount, note that the fabric ends up about 1 1/4 inches narrower than the bracket span. Add extra width to cover the whole window.
How to Measure for Roman Blinds
Roman blinds stack fabric at the top when raised. That stack needs headroom.
Measure the recess width in three places and take the smallest. Measure the drop and take the longest.
For outside mount, mount the blind 4 to 6 inches above the window. This keeps the stacked fabric off the glass.
How to Measure for Wood and Faux Wood Blinds
These blinds have thicker slats and deeper headrails. Depth matters most here.
Measure the width and height the same way as any inside mount. Then double check the depth against the product page.
Faux wood blinds get heavy in wide windows. Split very wide openings into two blinds on one headrail.
How to Measure for Cellular and Pleated Shades
Cellular shades fit shallow frames well. Many need under 1 inch of depth.
Measure the width in three places and take the smallest. Measure the height and take the longest.
Top down bottom up shades need a taller headrail area. Add extra height for outside mount versions.
How to Measure for Panel Track Blinds
Panel tracks slide across wide openings. The panels stack to one side.
Measure the full width you want covered. Add 4 inches per side for outside mount so the stack clears the glass.
How to Measure Windows for Blinds by Window Shape
Odd windows need a few extra steps. Here is how to handle the common ones.
Bay Windows
Treat every section as its own window. Never assume the sides match.
Measure each pane separately for width, height and depth. Number them from left to right on your sheet.
Check the corner posts. You need enough space so the headrails do not clash. Most makers cut the headrail corners to fit.
Bow Windows
Bow windows curve gently across several panes. Measure each pane on its own, just like a bay.
The angles between panes are shallower than a bay. Note the angle if your supplier asks for it.
Arched Windows
Measure the full width at the widest point of the arch. Then measure the height at the centre point.
Also measure the height of the straight section below the arch. Many buyers fit a standard blind below and a fixed arch above.
Sliding Glass Doors
Measure the full opening width, then add 3 to 4 inches per side. Mount the track 3 to 4 inches above the frame.
Vertical blinds and panel tracks suit these doors best. Both stack cleanly out of the walkway.
Check the handle position before you order. Set the stack to the opposite side.
French Doors and Door Windows
Door blinds must sit close to the glass. Measure the visible glass area first.
Then add 1 to 2 inches on each side for coverage. Keep the blind clear of the door handle.
Use hold down brackets so the blind stays still when the door moves.
Skylights
Many roof windows carry a size code on a metal plate. Look along the top of the sash.
Quote that code when you order and skip the measuring. If you cannot find it, measure the visible glass width and drop.
Corner Windows
Measure both windows separately. Then check the gap where the two blinds meet.
Reduce one blind by about 1 inch so the headrails clear each other.
Tiled Recesses
Kitchens and bathrooms often have tiles part way up the recess. The tiles narrow the opening.
Measure between the tiles as well as at the top. Use the narrower of the two numbers.
For roller blinds, compare both readings. If they differ by less than 1 inch, use the top measurement.
How to Measure to Replace Existing Blinds
You can measure the old blind instead of the window. This works well when the fit was already good.
Measure the headrail from end to end, including the brackets. That is your width.
Measure from the top of the headrail to the bottom rail. That is your height.
Tell your supplier you are replacing an existing blind. Ask for the exact size with no deductions.
If the old blind never fit properly, measure the window instead.
Metric and Imperial Conversion Chart
Many suppliers work in one system only. Use this chart to switch between them.
| Inches | Millimetres |
| 1/8 inch | 3mm |
| 1/4 inch | 6mm |
| 1/2 inch | 13mm |
| 1 inch | 25mm |
| 2 inches | 51mm |
| 3 inches | 76mm |
| 12 inches | 305mm |
| 24 inches | 610mm |
| 36 inches | 914mm |
| 48 inches | 1219mm |
| 60 inches | 1524mm |
| 72 inches | 1829mm |
Convert once and write both numbers down. Never convert twice, because errors build up fast.
9 Common Measuring Mistakes to Avoid
Most fitting problems come from the same handful of errors.
- Using a cloth tape measure. It stretches and reads long.
- Measuring only once. Windows are rarely perfectly square.
- Mixing up width and height. Always write W x H in that order.
- Making your own deductions. The factory already does this for you.
- Ignoring window depth. Your blind will stick out or refuse to fit.
- Forgetting handles and cranks. They block the blind from closing.
- Rounding to the nearest half inch. Use 1/8 inch steps instead.
- Assuming all windows match. Measure every single window.
- Measuring the old blind when it never fit. Measure the window instead.
Check every number twice before you order. Two minutes now saves weeks later.
Free Measuring Worksheet Template
Copy this simple table into a notebook or spreadsheet.
| Room | Window ID | Mount Type | Width 1 | Width 2 | Width 3 | Final Width | Height 1 | Height 2 | Height 3 | Final Height | Depth | Notes |
Fill one row per window. Add notes about handles, tiles or radiators.
Take a photo of each window too. It helps if you need advice later.
When You Should Ask for a Professional Measure
Do it yourself measuring works for most standard windows. Some jobs still deserve expert help.
Call a professional when you face any of these.
- Bay or bow windows with unusual angles
- Arched, circular or triangular windows
- Motorised blinds that need power and wiring planned
- Plantation shutters, which need very tight tolerances
- Large commercial openings and shop fronts
- Any window taller than a step ladder can safely reach
A professional measure usually costs little. It also transfers the risk of a wrong size to the fitter.
Final Thoughts
Measuring for blinds rewards patience more than skill. Use a steel tape, measure three times and write everything down. Pick your mount type first, then check the depth. Send the exact window size and let the factory make the deductions.
Follow these steps and your blinds will fit the first time. You avoid return shipping, delays and wasted money.
Still unsure about a tricky window? Send us your measurements and a photo. Our team will check them before your order goes into production.
Frequently Asked Questions
Measure the width in three places and the height in three places. For inside mount, use the narrowest width and the longest height. For outside mount, add 2 to 3 inches on each side. Record every number as width first, then height.
For inside mount, measure inside the frame opening. For outside mount, measure the area you want covered, including the trim.
No. Send the exact opening size. The maker applies the correct deduction during production.
Add 2 to 3 inches on each side and at least 3 inches above. For blackout blinds, add more on every side.
It depends on the blind. Mini blinds need about 3/4 inch. Faux wood blinds often need 2 1/2 inches. Vertical blinds need around 3 1/2 inches.
Measure the width in three places and take the smallest for inside mount. Take the shortest height so the vanes clear the sill. For outside mount, add 3 to 4 inches per side.
Use the same three point method. Take the narrowest width and the longest height. Mini blinds fit frames with as little as 3/4 inch of depth.
Yes. Choose mini blinds, cellular shades or slim roller blinds. You can also switch to outside mount.
Compare both diagonals. If they differ by more than 1/2 inch, choose outside mount. It hides the uneven edges.
Width always comes first. Every supplier reads sizes as width by height.
Measure the full opening width and add 3 to 4 inches per side. Mount the track 3 to 4 inches above the frame. Leave 1/2 inch of floor clearance.
Yes. Even windows that look identical often differ by half an inch or more.
