If you are trying to choose the right blinds for your windows, a blind size calculator is a useful starting point. It helps you estimate the width and drop you are likely to need based on your window measurements and whether you want an inside mount or outside mount. The calculator does not replace a supplier’s final sizing rules, but it makes the measuring process easier and gives you a practical recommendation before you shop.
Blind Size Calculator
Enter your window opening size and choose your fit type to get a recommended blind width and drop.
Inside Mount
Measure the width and drop inside the window recess. Best for a neat built-in look.
Outside Mount
Measure the opening and add overlap around the frame for better light blocking and privacy.
Your Recommended Blind Size
Cordless GII Morningstar 1" Light Filtering Mini Blind 28x64 - White
Cordless Light Filtering Mini Blinds for Indoor Windows - 34 Inch Width, 64 Inch Length, 1" Slat Size - Pearl White - Cordless GII Morningstar Window Blinds for Interior by Achim Home Decor
Joydeco No Drill Zebra Blinds for Windows, Cordless Day & Night Dual Sheer Roller Shades, Easy Installation, Free-Stop Lift System, Light Filtering Privacy Blinds for Home(White,48" W x 75" H)
This guide explains how our blind size calculator works, how to measure your windows correctly, what standard blind sizes are, how to figure out what size blinds you need, what custom size blinds are, how to cut blinds to size, and several other important things to know before buying blinds. If you are still comparing styles, you can also browse window blinds on Amazon to get a feel for the different options available.
How Our Blind Size Calculator Works
Our blind size calculator takes the basic window measurements you enter and uses them to suggest a recommended blind width and drop. The result changes depending on whether you choose an inside mount or an outside mount.
For an inside mount, the blind fits inside the window recess. Because the blind needs a little clearance to operate properly, the calculator subtracts a small allowance from the width and height. This helps avoid a fit that is too tight.
For an outside mount, the blind is installed outside the window opening, usually on the wall or trim. In that case, the calculator adds overlap to the width and drop so the blind covers more of the surrounding area. This usually improves privacy and reduces side light gaps.
- Inside mount usually subtracts a small fitting allowance.
- Outside mount usually adds overlap for better coverage.
- The final recommendation depends on your measurements, unit selection, and fit style.
- The result is best used as a starting point before checking the manufacturer’s sizing instructions.
How to Measure Your Windows for Blinds
Good blind sizing starts with good measuring. Even a small mistake can lead to blinds that rub against the frame, leave larger light gaps than expected, or simply do not fit properly.
Use a steel tape measure and write down each number clearly. Do not guess, round too early, or assume all windows in the same room are identical. A simple steel tape measure is one of the most useful tools you can have before ordering blinds.
How to Measure for Inside Mount Blinds
- Measure the width inside the window recess at the top, middle, and bottom.
- Measure the height inside the recess on the left, centre, and right.
- Use the smallest width measurement for the best fit.
- Use the smallest height if you want to be cautious about fit inside the recess.
- Check the recess depth to make sure the blind hardware can fit properly.
How to Measure for Outside Mount Blinds
- Measure the full width of the window opening.
- Measure the full height of the opening.
- Add extra width on both sides for overlap.
- Add extra height above and below the opening if you want better light blocking and privacy.
- Make sure nearby trim, handles, or furniture will not interfere with the blind.
Simple Measuring Tips
- Measure each window separately.
- Always measure in the same unit.
- Check for handles, locks, tiles, or trim that could affect the fit.
- Measure twice before ordering.
Cordless GII Morningstar 1" Light Filtering Mini Blind 28x64 - White
Cordless Light Filtering Mini Blinds for Indoor Windows - 34 Inch Width, 64 Inch Length, 1" Slat Size - Pearl White - Cordless GII Morningstar Window Blinds for Interior by Achim Home Decor
Joydeco No Drill Zebra Blinds for Windows, Cordless Day & Night Dual Sheer Roller Shades, Easy Installation, Free-Stop Lift System, Light Filtering Privacy Blinds for Home(White,48" W x 75" H)
How to Figure Out What Size Blinds You Need
The blind size you need depends on more than the opening itself. You also need to think about how the blind will mount, what type of blind you want, how much privacy you need, and whether you want a more built-in look or more coverage.
If you want a cleaner and more fitted appearance, inside mount is often the preferred option. If you want stronger privacy, better room darkening, or fewer light gaps, outside mount is often the better choice.
- Choose inside mount if your recess is deep enough and you want a neat built-in look.
- Choose outside mount if your recess is shallow or you want better coverage.
- Roller blinds often have side light gaps on inside mounts because the fabric is usually narrower than the full bracket width.
- Roman blinds and blackout blinds often benefit from outside mount sizing if coverage matters.
If you are weighing different room-darkening options, it can help to look through blackout window blinds and roller blinds to compare how different designs affect coverage.
What Are the Standard Size Blind Sizes Available?
Standard blind sizes are the common ready-made sizes sold in stores and online. These vary by retailer, brand, and blind type, so there is no single universal standard that applies to every product.
In many cases, standard blind widths are offered in regular steps, and the same is true for common drops. This is why some windows fit off-the-shelf blinds quite well while others fall between sizes.
- Common ready-made widths may include sizes such as 45 cm, 60 cm, 90 cm, 120 cm, and 150 cm.
- In inch-based sizing, common widths may include 18 inch, 24 inch, 36 inch, 48 inch, and 60 inch options.
- Common drops may include short, medium, and long lengths depending on the product range.
- Standard sizes are often the fastest and most affordable option if your window fits them closely.
If your calculator result is very close to a standard size, you may be able to buy an off-the-shelf blind instead of ordering custom. Always compare your result with the exact size chart for the product you want, because one retailer’s sizing can differ from another’s. To see what ready-made options look like, you can browse ready-made window blinds.
What Custom Size Blinds Are
Custom size blinds, also called made-to-measure blinds, are manufactured to fit your exact dimensions rather than being sold in fixed standard sizes. They are especially useful for windows that are unusually wide, unusually tall, or simply fall between the standard sizes available in stores.
Custom blinds are usually a better choice when you want a more precise fit, a more polished finished look, or a specific material or control style that is not easy to find off the shelf.
- Custom blinds are made to the measurements you provide.
- They are useful for awkward or non-standard windows.
- They often cost more than ready-made blinds.
- They may have longer lead times and more limited return options.
If your windows are large or unusual, it can still help to review custom size blinds and related accessories before deciding which route makes the most sense.
What Blind Type Means for Sizing
Different blind types can behave differently even when the same window measurements are used. That is why the blind type matters when checking your final order details.
Roller Blinds: Roller blinds are simple and popular, but the fabric width is often narrower than the full bracket-to-bracket width. This means some side light gap is normal, especially on an inside mount. You can compare different roller window blinds to see how product sizing is usually presented.
Roman Blinds: Roman blinds are softer and more decorative. They often look especially good on outside mounts because they can cover the opening more generously and create a fuller appearance. If you like a softer fabric look, browse Roman shades.
Venetian Blinds: Venetian blinds are commonly available in standard sizes and may sometimes be more adjustable than some fabric blind styles. Slat size and headrail depth still matter when checking fit. It may help to compare Venetian blinds in both aluminium and faux wood styles.
Vertical Blinds: Vertical blinds are often used for wider openings such as large windows and sliding doors. Width, track placement, and overlap are especially important when sizing them correctly. For wider openings, take a look at vertical blinds to compare common configurations.
Cordless GII Morningstar 1" Light Filtering Mini Blind 28x64 - White
Cordless Light Filtering Mini Blinds for Indoor Windows - 34 Inch Width, 64 Inch Length, 1" Slat Size - Pearl White - Cordless GII Morningstar Window Blinds for Interior by Achim Home Decor
Joydeco No Drill Zebra Blinds for Windows, Cordless Day & Night Dual Sheer Roller Shades, Easy Installation, Free-Stop Lift System, Light Filtering Privacy Blinds for Home(White,48" W x 75" H)
How to Cut Blinds to Size
Some blinds can be cut down or trimmed, but not every blind is suitable for this. Whether trimming is possible depends on the blind type, material, headrail design, and the manufacturer’s instructions.
If you are considering cutting blinds to size, check the product guidance first. Some blinds can be damaged or become difficult to operate if they are trimmed incorrectly.
- Some faux wood blinds and venetian blinds may be easier to trim than other styles.
- Some roller blinds may also be trimmable, depending on the model.
- Roman blinds, premium blind systems, and motorised blinds are usually less suitable for DIY trimming.
- If you cut too much off, the blind cannot be restored.
Basic Tips for Cutting Blinds to Size
- Read the manufacturer’s instructions first.
- Mark the reduction carefully before cutting.
- Use the right tools for the material.
- Trim slowly and test fit before final installation.
- When in doubt, buy the right size instead of trying to modify the blind.
If you plan to do any trimming yourself, useful items to compare include a utility knife, a straight edge ruler, and a set of clamps.
Common Mistakes When Measuring for Blinds
Many blind fitting problems come from small measuring mistakes rather than product defects. Taking a little extra time before ordering can save a lot of frustration later.
- Measuring only once instead of checking several points.
- Choosing the wrong mount style before measuring.
- Ignoring recess depth for inside mount blinds.
- Forgetting about handles, locks, tiles, or trim.
- Assuming the quoted blind width always matches the visible fabric width.
- Using one window’s measurements for every window in the room.
Inside Mount vs Outside Mount Blinds
Inside mount and outside mount blinds each have advantages. The better option depends on the look you want and how your window is built.
Inside Mount Advantages
- Cleaner and more built-in appearance.
- Works well for modern interiors.
- Keeps the blind contained neatly within the frame.
Inside Mount Disadvantages
- Requires enough recess depth.
- Can produce more side light gaps with some blind types.
- Needs more careful measuring to avoid a tight fit.
Outside Mount Advantages
- Better coverage for privacy and light control.
- Useful when the recess is shallow or unsuitable.
- Can make the window look larger visually.
Outside Mount Disadvantages
- Takes up more wall space around the window.
- Needs more thought about trim, corners, and nearby furniture.
- May look less built-in than an inside mount.
Should You Buy Standard or Custom Blinds?
If your measurements are close to a standard size and the product size chart works for your window, standard blinds can be the easiest and most affordable option. If your window does not match standard sizing well, custom blinds are usually the safer route.
- Choose standard blinds if cost and speed matter most.
- Choose custom blinds if fit, finish, and exact sizing matter most.
- Check whether the brand makes its own deductions before placing a custom order.
Extra Tips Before Ordering Blinds
- Measure first and shop second.
- Check product charts instead of relying only on general size advice.
- Confirm whether the listed width is the overall blind width or just the fabric width.
- Think about blackout, moisture resistance, privacy, and child safety before choosing a blind type.
- For bedrooms and media rooms, outside mount often helps with better light control.
Depending on the room, you may also want to compare cordless blinds, faux wood blinds, or room darkening shades based on your budget and the level of light control you want.
Blind Size Calculator FAQ
Should blinds be wider than the window?
For outside mount blinds, usually yes. A blind that is wider than the window opening generally gives better privacy and reduces side light gaps. For inside mount blinds, the blind should fit within the recess instead.
Is it better to size up or size down for blinds?
That depends on the mount type. For inside mount blinds, going too large can cause fitting problems. For outside mount blinds, sizing up slightly can improve coverage.
Can I buy one blind size for every window in a room?
You should measure each window separately. Even windows that look identical can vary enough to affect blind fit.
Do blackout blinds need different measurements?
The measuring process is similar, but blackout blinds usually benefit from extra overlap and fewer side gaps. That is one reason outside mount is often chosen for better blackout performance.
What if my measurements fall between two standard blind sizes?
Compare your measurements with the supplier’s exact size chart and deduction rules. If the fit looks uncertain, a custom-size blind is often the better option.
Final Thoughts
A blind size calculator makes the buying process easier by turning your window measurements into a practical size recommendation. It is most useful when paired with careful measuring and a quick review of the manufacturer’s sizing rules. Whether you choose standard blinds, custom blinds, inside mount, or outside mount, a little planning before ordering can help you get a better fit, better light control, and a better overall result.
Cordless GII Morningstar 1" Light Filtering Mini Blind 28x64 - White
Cordless Light Filtering Mini Blinds for Indoor Windows - 34 Inch Width, 64 Inch Length, 1" Slat Size - Pearl White - Cordless GII Morningstar Window Blinds for Interior by Achim Home Decor