How Do I Measure My Windows for Custom Blinds? Step by Step

Start with a clean window, a steel tape, and one worksheet line per window.

How do I measure my windows for custom blinds? Choose inside or outside mount first, then use a steel tape to measure width and height at three points each, record every number to the nearest 1/8 inch as width by height, and check frame depth. Inside mounts use the narrowest width; outside mounts add overlap.

Key Takeaways

• Mount type comes first. An inside mount uses the opening between the frame sides; an outside mount uses the area you want covered plus overlap.

• Take three readings per dimension. Measure width at the top, middle, and bottom, then height at the left, center, and right, and apply the rule your product requires.

• Rounding and order matter. Record to the nearest 1/8 inch with a steel tape, width first, and label each window separately.

• The height rule varies by seller. Many guides say to submit the longest inside-mount height, while at least one major retailer says the shortest, so follow your product's instruction sheet.

• Depth decides feasibility. Some seller guides cite roughly 3/4 inch as a minimum for basic inside-mounted blinds, and shallow frames usually call for an outside mount.

• Hard windows deserve a professional. Home Blinds and Floors measures every window on site during a free in-home consultation across the Delmarva Peninsula.

A custom blind is built to the number you give it, so the tape measure is the most important tool in the project. Go a quarter inch too wide and an inside-mount blind jams against the frame. Go a quarter inch too narrow and a strip of daylight hits the bedroom at 6 a.m. Homes are not cheap in Grasonville, MD either: the March 2026 median listing price was $656,950, according to Realtor.com Economic Research, so a crooked or leaky blind shows.

At Home Blinds and Floors, we have measured windows in Rehoboth Beach, DE cottages and in waterfront homes on Kent Island, MD, and the same handful of errors cause most remakes. The wrong mount choice and ignored depth top the list, along with taking a single reading instead of three. This guide walks through each decision in the order you will face it.

You will learn how to choose a mount, take readings, handle shallow frames, and troubleshoot out-of-square openings. Measuring windows for custom blinds is a patient job rather than a hard one, and a careful first pass typically takes 5 to 10 minutes per window.

What Tools and Setup Do You Need Before You Measure Windows for Blinds?

A blind-measuring setup is a rigid steel tape measure, a pencil, a worksheet, and a stepladder for anything above shoulder height. Steel matters because cloth tapes sag across a 72-inch sliding door. Custom blinds are cut to fractions of an inch, so a small reading error carries straight into the finished product.

• Steel tape measure: choose one marked in 1/8 inch increments with a locking blade.

• Worksheet: make columns for window label, mount type, width, height, depth, and notes.

• Stepladder: a stable one beats stretching from a chair at a tall stairwell window.

• Phone camera: photograph handles, cranks, and trim so you can check obstructions later.

Number every window before you pick up the tape. Names such as Kitchen 1 or Sunroom North keep the worksheet readable, and a label like Primary Bedroom Slider tells you exactly which opening a number belongs to. Measure each frame on its own, even when two windows look identical, because framing drifts from opening to opening. You will see this most in older cottages around Lewes, DE and the historic streets of Easton, MD, where a frame can differ by a quarter inch or more from its neighbor.

A bright and airy sunroom or sitting area featuring expansive arched windows with white plantation shutters, wooden rattan chairs with cushions, and a combination of hardwood and tile flooring. The space exemplifies modern coastal or contemporary design with abundant natural light and elegant architectural details.

What Is the Difference Between Inside Mount and Outside Mount Blinds?

An inside mount places the blind within the window frame, flush with the casing, while an outside mount attaches to the wall, trim, or ceiling above the frame and covers the opening plus overlap. You must choose before measuring, because each method uses different numbers and different readings.

Factor	Inside mount	Outside mount
Appearance	Recessed, clean look that shows the trim	Covers the frame; can make a window look larger
Light control	Small edge gaps are common	Overlap blocks most edge light
Depth needed	Enough frame depth for the headrail	Works on shallow or flat frames
What you measure	The exact opening	The area to cover plus overlap
Best for	Deep frames and trim worth showing	Shallow frames, uneven openings, privacy-first rooms

Our take: choose an inside mount when the frame is deep and square, as in many newer builds in Middletown, DE. Choose an outside mount when privacy and darkness matter more than looks. Even blackout-rated bedroom blinds leak light at the edges when an inside-mount fit is loose.

Even blackout-rated bedroom blinds can leak light if the inside-mount fit isn't tight.

Which Blinds Work Best for Shallow Window Frames?

Shallow frames are the most common reason an inside mount fails. Some seller guides cite a minimum depth of roughly 3/4 inch for basic inside-mounted blinds, and cellular, roller, and wood products often need more. Your exact minimum comes from the product's specification sheet, so check it before you order.

When the frame falls short, switch to an outside mount rather than forcing a blind into the opening. Slim-profile roller shades and faux wood blinds both mount cleanly on the wall or trim. In humid rooms near the coast, material matters as much as depth, and our comparison of faux wood versus real wood blinds covers how each handles moisture.

How Do I Measure My Windows for Custom Blinds, Step by Step?

Measuring windows for custom blinds is a sequence of eight checks: pick a mount, gather tools, label windows, take width readings, take height readings, check depth, apply the mount rule, and record the numbers. Following the order below prevents the two most common errors, mixing mount rules and trusting a single reading.

1. Choose inside or outside mount. Check frame depth and decide how much light control and trim visibility you want.

2. Set up your tools. Use a steel tape, a pencil, a worksheet, and a ladder.

3. Label each window. Give every opening a name and measure it individually, even if neighbors look the same.

4. Measure width in three places. Read the top, middle, and bottom of the opening. For an inside mount, use the narrowest reading.

5. Measure height in three places. Read the left, center, and right. Apply your seller's rule, which is most often the longest reading for an inside mount.

6. Measure depth. Run the tape from the front edge of the frame to the glass or first obstruction, and compare it with the product minimum.

7. Apply outside-mount allowances if needed. Add overlap to the sides and start above the frame to clear hardware.

8. Record and re-check. Write width by height to the nearest 1/8 inch, note every obstruction, and re-measure before ordering.

One caution before you subtract anything: for inside-mount orders, most custom blind makers want the exact opening size, and they apply any required clearance themselves. Some online ordering systems instead ask you to deduct a fraction of an inch. Always confirm which approach your seller uses before you write the final number, because deducting twice produces a blind that is visibly too narrow.

How Do You Measure for an Inside Mount Without Gaps or Rubbing?

Inside-mount measuring means recording the exact opening between the frame sides, then using the narrowest width and whichever height your product's instructions specify. Three readings per dimension guard against frames that are out of square, which is common in older homes in Easton, Annapolis, and Lewes.

The U.S. Department of Energy's Building America Solution Center publishes measuring guidance for cellular blinds that follows this same logic: width across the top, middle, and lower third, then the shortest reading, and height three times, then the longest. Other guides place the readings slightly differently, but the three-point principle holds.

How Do You Measure Window Width for an Inside Mount?

Hold the tape tight from one inside edge of the frame to the other, reading at the top, middle, and bottom. Write down all three. Submit the smallest, because a blind cut to the smallest reading will fit at every point, while one cut to the largest will bind at the tightest spot.

How Do You Measure Window Height for an Inside Mount?

Measure from the top of the opening down to the sill at the left, center, and right. Then check how your seller wants the number. A longer height lets the blind reach the sill on the low side of a sloping sill, while a shorter reading keeps it from touching on the high side. The next section explains why guides disagree.

How Do You Measure Window Depth for Inside-Mount Blinds?

Window depth is the distance from the front edge of the frame back to the glass or the first obstruction, such as a crank, latch, tilt lock, or casement handle. Measure at several spots along the frame, because glazing stops and sash positions are not always flush. Then compare the smallest depth with the headrail requirement for your product.

An obstruction counts even if it is small. A single crank handle that protrudes an inch can stop a roller shade from hanging straight. If a handle sits in the way, you can often move to an outside mount rather than replace the hardware.

How Do You Measure for an Outside Mount and Add the Right Overlap?

Outside-mount measuring means recording the area you want covered rather than the glass opening, then adding overlap so the blind hides the frame edges and blocks edge light. Seller guidance ranges from about 1 inch to 2 1/2 inches of overlap per side, depending on the product and how much coverage you want. Pick the larger end of the range for bedrooms and bathrooms.

How Much Overlap Does Each Side Need?

Overlap depends on the product. Building America Solution Center guidance suggests at least 1 inch of added width per side for cellular blinds, while some manufacturers recommend 2 1/2 inches per side. Seller guides for roller and solar shades go further, with one citing at least 2 1/4 inches per side. For privacy in a bathroom or bedroom, choose the larger allowance.

West-facing windows on the Chesapeake side, such as bay-view picture windows in Grasonville, throw low afternoon sun straight at the frame edges. In those rooms, extra overlap is the cheapest way to cut glare around the sides of the blind.

Where Should the Blind Start and End?

Start the blind at least 3 inches above the top of the frame so the brackets and headrail clear the trim. That figure comes from several measuring guides, and the Building America Solution Center notes that some manufacturers suggest starting 3 inches above the trim and extending 2 inches below it or to a protruding sill. Measure the total height you want to cover, not the glass.

What Obstructions Change an Outside-Mount Measurement?

Handles, cranks, crown molding, and casing depth all alter where brackets can land. Mark any obstruction on your worksheet and photograph it. The headrail itself also takes space, so a deep cassette or valance can interfere with trim that looks flat on the wall.

A bright and airy living room featuring a modern mid-century design with a black leather and wooden armchair, terracotta tile flooring, and large horizontal shutter windows that flood the space with natural light. The room showcases a warm wooden ceiling, neutral white walls, and a glimpse into an adjacent bedroom with hardwood floors.

Should You Submit the Longest or the Shortest Height Reading?

The inside-mount height you submit depends on the seller's ordering rule, because published guides disagree: many tell you to use the longest of three readings, while at least one major retailer tells you to use the shortest. Check your product's instruction sheet before writing the number down, because the rule is built into how the blind is fabricated.

The disagreement exists because some sellers deduct a small amount from your numbers internally, and others expect you to do it. A seller that asks for exact numbers can accept the longest height, since the blind is cut slightly shorter at the factory. A seller that asks you to deduct a quarter inch from height, and a quarter to a half inch from width, expects the shortest reading to stay safe.

From our experience at Home Blinds and Floors, this is why mixed measurements cause remakes: a homeowner follows one guide's width rule and another's height rule. We measure on site and submit the numbers in the format the manufacturer expects, so the deduction question never lands on you.

Does the Measurement Mean the Whole Blind or Just the Fabric?

Overall product width is the full measurement of headrail, brackets and fabric together, while fabric width is narrower. One published guide notes that shade fabric sits roughly 5/8 inch in from the product edge on each side. A cassette or valance adds more width and depth that rarely appears in generic guides.

Ask whether your measurement describes the complete product or the fabric. This matters most for bedrooms, where visible fabric edges at the frame let light through. Light-filtering cellular and roller shade options have headrail and side-gap details that differ by product, so confirm them before you order.

Which Measuring Rules Change by Mount Type at a Glance?

Measurement rules for custom blinds are the readings and allowances that tell you what to record for each mount type. The table below compiles ranges from the U.S. Department of Energy's Building America Solution Center and common seller guides in 2026, and your product's instruction sheet overrides every general figure here.

Measurement	What to record	What varies by seller
Inside width	Three readings; use the narrowest	Some ask you to deduct 1/4 to 1/2 inch
Inside height	Three readings; follow the seller's rule	Longest for most; shortest for some
Depth	Front edge to first obstruction	Product-specific minimum
Outside width	Covered area plus overlap per side	Roughly 1 to 2 1/2 inches per side
Outside height	Start above the frame, end below trim or sill	Start point and extension differ
Rounding and order	Nearest 1/8 inch, width first	Rarely varies

Two lines in this table cause the most trouble: the height rule and the overlap range. Treat them as questions to ask before you measure rather than figures to memorize. If your seller gives no guidance on either, call and ask before you order.

How Do You Measure Odd Windows, Non-Square Frames, and Sliding Doors?

A non-square window is an opening where opposite sides or corners differ in size, so the same width or height changes from one reading to the next. Measure both diagonals; if they do not match, the frame is out of square, and you should treat the narrowest reading as the working width. A difference of more than 1/4 inch between diagonals is a good signal to consider an outside mount or a professional visit.

What Should You Do With Bay, Arched, and Curved Windows?

Bay windows need each section measured separately, and the angled returns are best left to an installer. Arched and curved tops call for templates or specialty fabrication rather than a single width and height. Our guide to arched window treatments covers what options exist.

How Do You Measure Sliding Glass Doors and Floor-Length Windows?

For sliding doors in an Ocean City, MD condo or a Bethany Beach, DE beach house, measure the full width you need to cover, including the stack space for vertical treatments. Mount above the track or on the ceiling, and leave clearance so the covering does not drag on the floor. Our guide to window treatments for sliding glass doors compares your options.

Why Are Shutters Different From Blinds?

Plantation shutters are the one product we rarely recommend measuring yourself. Frames in older coastal homes swell, shift, and settle, and the shutter has no fabric to forgive a quarter inch. At Home Blinds and Floors, we check the opening, the humidity exposure, and the hinge clearance on site before fabrication. If you are weighing custom plantation shutters, ask for a professional measure first.

A bright and modern living room featuring a comfortable beige sectional sofa with turquoise and grey patterned pillows, positioned in front of large windows with roller blinds that overlook a lush forest view. The space includes a minimalist desk area, white storage units with turquoise accents, hardwood flooring, and contemporary pendant lighting.

What Measuring Mistakes Cost Homeowners the Most?

A measuring mistake is any recorded number that does not match the final fit, and the six below account for most remakes. Each carries a direct consequence, such as a blind that jams, a visible gap, or a headrail that clashes with trim.

Mistake	Typical result	Fix
Using one reading per dimension	Binding or gaps in out-of-square frames	Take three readings and apply the rule
Mixing seller rules	Wrong deduction applied twice or not at all	Follow one set of instructions
Ignoring depth	Headrail sticks out of the frame	Measure depth and compare with the spec sheet
Skipping obstructions	Handle or crank blocks the blind	Photograph and note every obstruction
Using a cloth or loose tape	Reading drifts across wide windows	Use a locking steel tape
Rounding up to a clean number	Blind too wide to install	Record to the nearest 1/8 inch

The most expensive of these is the first one, because it is invisible until the blind arrives. Re-measure the next morning with fresh eyes and you will catch most of them before you order.

When Is It Worth Having a Professional Measure for You?

Professional measuring means an installer visits your home, measures each window on site, and checks mount depth, obstructions, and sun exposure before anything is ordered. It is worth it for shutters, motorized shades, tall or arched windows, and any frame that fails the diagonal check.

For a standard double-hung window in a spare room with a deep, square frame, careful DIY measuring works fine. We would rather tell you that than sell you a visit you do not need. Once you add several windows, a sliding door, or a motorized system, the cost of one wrong number usually outweighs the cost of getting help.

Home Blinds and Floors offers a free in-home consultation across the Delmarva Peninsula, from Rehoboth Beach and Lewes to Easton, Salisbury, and Annapolis. We measure on site and match the material to the room before ordering, which avoids the gaps and crooked headrails that DIY jobs often show. Browse custom blinds for Delmarva homes or read reviews from local homeowners. If budget is the question, see what custom blinds cost on Delmarva.

How Should You Double-Check Your Numbers Before Ordering?

A pre-order check is a short review of every recorded number against the window itself, your mount choice, and the product specification. It takes about five minutes and catches the typos and transposed digits that turn a good measure into a remake.

• Re-measure two or three windows the next day and compare them with your worksheet.

• Confirm that width is listed before height for every window.

• Check each depth against the minimum for the product you chose.

• Review your photos for obstructions you forgot to write down.

• Ask your seller whether they deduct clearance or expect you to.

If you are ordering for a nursery or children's room, also choose cordless or motorized options. Federal rules treat long accessible cords as a strangulation hazard for young children, and the U.S. Consumer Product Safety Commission publishes current window covering guidance. Cordless lift systems also change the headrail depth, so tell your installer before you finalize the measurements.

What Should You Do Next Before You Order Custom Blinds?

Knowing how to measure your windows for custom blinds comes down to a few habits: pick the mount first, take three readings per dimension, follow your seller's height rule, record to the nearest 1/8 inch, and check depth before you commit. Those steps hold for any home in 2026, whether it is a new build in Middletown or a 1920s cottage in Lewes.

The right window treatment fits your windows, your climate, and the way you live. Whether you are protecting a beach house from sun and salt air or updating a home office, a careful measurement and an honest recommendation make the difference. At Home Blinds and Floors, that is how we approach every home and business on the Delmarva Peninsula.

Humid, salt-laden coastal air is hard on natural wood shutters.

If this guide helped you narrow down your options, the next step is easy. Request a quote for your windows and we will visit your home, measure each opening, and walk through blind, shade, and shutter choices during a free in-home consultation.

Frequently Asked Questions

How do you measure for blinds?

Decide on an inside or outside mount, then measure width and height at three points each with a steel tape. Record the numbers to the nearest 1/8 inch, width first, and check frame depth for an inside mount. Use the narrowest width for an inside mount, or add overlap for an outside mount.

How do you measure blinds you already have?

Measure the window opening instead of the old blind. Previous blinds may have been cut for different frames or include headrail space that misleads you. Use the old blind only as a rough cross-check after you take your own readings.

How many places should you measure each window for blinds?

Measure width in three places (top, middle, and bottom) and height in three places (left, center, and right), so you take six readings per window, plus depth. If a diagonal check shows the frame is out of square, the three-point readings tell you which number to submit.

Should you subtract anything from an inside-mount measurement?

On many custom orders, you submit the exact opening size and the manufacturer applies any required clearance. Some online ordering systems ask you to deduct a fraction of an inch instead. Confirm your seller's method before you finalize the numbers.

What are the best custom blinds for shallow window frames?

Slim-profile blinds and roller shades work best on an outside mount, which does not depend on frame depth. Check the product's minimum depth before choosing an inside mount, because cellular and wood options often need more space. An on-site check settles it quickly.

What if your windows are not square?

Measure both diagonals; if they differ, the frame is out of square. Take three readings in each direction and use the narrowest width for an inside mount. An installer can confirm the fit on site and advise whether an outside mount is the safer choice.

Who can measure my windows for custom blinds on the Delmarva Peninsula?

Home Blinds and Floors is a locally owned window treatment company that measures windows during a free in-home consultation across the Delmarva Peninsula. The team serves communities from Rehoboth Beach, Lewes, and Ocean City to Easton, Grasonville, Kent Island, and Annapolis. You can also compare any provider on process, product range, and installation follow-up.

Do shades and shutters measure differently from blinds?

Yes, in the details. Roller and solar shades often need larger overlap on an outside mount, and fabric sits narrower than the overall product width. Plantation shutters need a precise on-site fit, so a professional measure is the safer route.

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