How to Measure Windows for Perfect Fit Blinds and Shades

Are you considering replacing old windows with new window treatments, or simply updating your current blind and shade options? Getting accurate window measurements is the foundation of a successful home improvement project. One wrong measurement can lead to costly mistakes, delays, and window treatments that don’t fit properly.

At Blinds of Sacramento, we’ve helped thousands of Sacramento homeowners learn how to measure windows correctly for perfect-fit blinds and shades. Whether you’re planning an insert replacement or a full-frame replacement, or simply measuring for new window treatments, this step-by-step guide will walk you through everything you need to know.

If you’d prefer professional help, we offer free in-home consultations throughout the Sacramento area, where we’ll measure your windows and help you find the perfect window treatment solution.

Why Accurate Window Measurements Matter

Before you measure a window, it’s important to understand why precision matters. Window measurements directly impact the fit, function, and appearance of your blind or shade installation.

Avoiding Costly Mistakes: When you measure your windows incorrectly, custom blinds and shades manufactured to those specifications won’t fit properly. You may need to reorder, which means additional costs and extended wait times. Taking the time to measure the width and height accurately from the start saves money and frustration.

Ensuring Proper Function: Window treatments that don’t fit correctly may not operate smoothly. Blinds that are too wide won’t fit inside the window frame. Shades that are too short leave gaps that compromise privacy and light control. Whether you’re installing inside mount or outside mount treatments, accurate measurements ensure smooth operation.

Maximizing Energy Efficiency: Properly fitted window treatments create better insulation. When measuring for replacement windows or window coverings, precise dimensions ensure there are no gaps where heated or cooled air can escape—especially important during Sacramento’s hot summers when your existing frame needs adequate coverage.

Essential Tools You Need to Measure

Before you begin measuring, gather these simple tools:

Metal Tape Measure: This is your most important tool. A metal tape measure provides consistent, accurate measurements that won’t stretch or sag like cloth alternatives. Choose one that extends at least 25 feet to handle larger windows and sliding glass doors.

Notepad or Smartphone: You’ll record three measurements for each window dimension. Keep detailed notes including window location and all measurement data. Taking photos can also help you remember the parts of a window and any obstacles.

Step Stool or Ladder: For windows positioned high on the wall, you’ll need safe access to measure the distance from the top jamb to the sill accurately.

Helper (Optional): For larger windows, double-hung window configurations, or casement windows, having assistance makes the measurement process easier and more accurate.

Understanding Inside Mount vs. Outside Mount

Before you measure window openings, you need to decide between inside mount and outside mount installation. This choice affects how you’ll measure and what dimensions you need to record.

Inside Mount Installation

An inside mount means the window treatment is installed inside the window frame, creating a clean, built-in appearance. The treatment sits within the existing frame, showcasing any decorative casing or trim.

When to choose inside mount:

Your window frame has sufficient depth (minimum 2-3 inches depending on the product)
You want to display decorative window trim or casing
You prefer a sleek, minimalist appearance
The window frame is square and the jamb to jamb measurement is consistent

Depth Requirements:

Measure the inside of the frame from the inside edge to the glass
Horizontal blinds need minimum 2 inches
Cellular shades need 2-3 inches
Plantation shutters need 3-3.5 inches minimum

Outside Mount Installation

An outside mount means the treatment is installed on the wall or casing surrounding the window opening, covering the entire existing frame.

When to choose outside mount:

Your window frame is too shallow for inside mounting
You want maximum light control with no side gaps
You’re working with a rough opening that isn’t perfectly square
You want to make the window appear larger
Your old window has obstructions like cranks or moving parts

Step-by-Step Guide: How to Measure for Inside Mount

For inside mount installations, precision is critical. Follow these easy steps carefully:

Measuring Width (Jamb to Jamb)

Measure from jamb to jamb at three different spots: Run your tape measure across the window opening at the top, middle, and bottom. Measure from the inside edge of the left side jamb to the inside edge of the right side jamb.
Record all three measurements: Don’t assume the window is perfectly square—many aren’t, especially in older homes with an existing frame that may have settled over time.
Use the smallest width measurement: Always use the narrowest measurement. This ensures your window treatment will fit even if the jamb spacing varies.
Don’t make deductions: Record the exact measurement to the nearest 1/8 inch. The manufacturer will automatically undersize the treatment for proper fit and operation.

Measuring Height

Measure the distance at three points: Measure from the head jamb (top inside edge) to the sill at the left side, center, and right side of the window opening.
Record all three measurements: Window frames can be uneven, especially in double-hung window configurations common in Sacramento homes.
Use the smallest measurement: Select the shortest height to ensure the treatment fits properly without binding.
Measure to the window sill: If your window has a sill, measure the height to where you want the bottom of the treatment to rest—typically the sill surface.

Checking Depth and Obstructions

The depth of your window frame determines whether inside mount is possible:

Measure from the inside edge to the glass: This measurement tells you how much space is available for the treatment mechanism.
Check minimum requirements:
- Horizontal blinds: 2 inches minimum
- Cellular/honeycomb shades: 2-3 inches depending on style
- Roller shades: 2 inches minimum
- Plantation shutters: 3-3.5 inches minimum
Note any obstructions: Look for window cranks, locks, handles, or other moving parts that might interfere with the treatment. These are especially common in casement windows.

Recording Your Window Measurements

For each window, document:

Location (e.g., “Living room, west window”)
Width measurements (top, middle, bottom)
Smallest width to use
Height measurements (left, center, right)
Smallest height to use
Depth measurement
Any obstructions or special notes

Example notation:
Master Bedroom, North Window (double-hung window)

Width: 35.5″ (top), 35.75″ (middle), 35.5″ (bottom) → Use smallest: 35.5″
Height: 48″ (left), 48.25″ (center), 48.125″ (right) → Use smallest: 48″
Depth: 3 ¼ inches
Notes: Window crank on right side

Step-by-Step Guide: How to Measure for Outside Mount

Outside mount measurements offer more flexibility but still require careful attention to avoid costly mistakes.

Measuring Width for Outside Mount

Measure the window opening: First, measure the exact width of the window frame or casing from outside edge to outside edge.
Add overlap for coverage: Add at least 3-4 inches to each side (6-8 inches total width) to ensure adequate light blockage and privacy. This overlap prevents light gaps at the edges.
Consider wall space: Ensure you have enough flat wall surface on each side for mounting brackets. Check for obstructions like light switches or drywall irregularities.
Account for stacking: If you’re ordering blinds or shades that stack when raised, ensure the headrail won’t block your view or interfere with the top jamb area when the treatment is open.

Measuring Height for Outside Mount

Determine top placement: Measure the distance from where you want the top of the treatment installed. This is typically 3-4 inches above the window frame or at the top of the casing.
Decide on bottom placement: Measure to where you want the treatment to end—typically 3-4 inches below the window frame, to the window sill, or to the floor for larger windows.
Calculate total height: The total height is the distance from your chosen top placement to your chosen bottom placement.

Recording Outside Mount Measurements

For each window, record:

Location and window type
Exact window opening width
Desired total width (including overlap)
Exact window opening height
Desired mounting height above window
Desired length below window
Total height measurement
Any obstructions or notes

Measuring Special Window Situations

Not all windows are standard rectangles. Here’s how to handle special cases:

Measuring Replacement Windows

If you’re measuring for replacement windows that will also need new treatments:

Measure the rough opening if doing a full-frame replacement
Measure the existing frame dimensions if doing an insert replacement or replacement unit installation
Note the window size for both the opening and the replacement window specifications
Consider how the new windows will affect your window treatment measurements

Double-Hung Window Configurations

Double-hung windows are common in Sacramento homes:

Measure the full height from head jamb to sill
Note if there are any protruding locks or moving parts between the window panels
Check that the side jamb is straight and consistent
Measure depth at both the top inside and bottom inside of the frame

Single-Hung Window Measurements

For a single-hung window (where only the bottom panel moves):

Follow the same measuring process as double-hung windows
Note which panel operates
Check for obstructions where the panel slides

Casement Window Considerations

Casement windows that crank outward require special attention:

Measure the opening as you would for standard windows
Note the location and projection of the crank handle
Consider outside mount if the crank interferes with inside mounting
Measure the distance the handle extends into the room

Measuring for Sliding Glass Doors

Sliding doors present unique challenges:

Measure the full width and height of the door opening
Note which direction the door slides
Consider vertical blinds or panel track shades designed for wide openings
Ensure the treatment won’t interfere with door operation or the horizontal piece at the top

Common Measurement Mistakes to Avoid

Even experienced DIYers can make these errors. Here’s how to avoid them:

Using the Wrong Tape Measure: Never use a cloth tape measure that can stretch. Always use a metal tape measure for window measurements.

Measuring Only Once: Windows are rarely perfectly square. Always take three measurements for both width and height, then use the smallest measurement for inside mounts.

Forgetting to Double Check: After recording your measurements and make notes, go back and double check each one. Measure the inside dimensions again to verify accuracy.

Not Measuring Depth: For inside mounts, depth is just as important as width and height. Insufficient depth is one of the most common reasons inside mount won’t work.

Rounding Measurements: Record exact measurements to the nearest 1/8 inch. Don’t round up or down—the manufacturer will subtract the necessary clearances.

Assuming Identical Windows Are the Same: Even windows that appear identical may have slight variations. You need to measure each window individually.

Ignoring the Parts of a Window: Understanding window components—head jamb, side jamb, sill, casing—helps you know how to measure correctly and communicate with professionals.

Not Noting Obstructions: Ceiling fans, light fixtures, furniture, or architectural features can interfere with operation. Document everything in the area.

Forgetting About Drywall or Trim: When planning outside mounts, ensure mounting surfaces are solid. Some areas may have drywall that needs a stud for secure installation.

Not Considering Replacement Process Needs: If you’re also replacing windows, coordinate measurements and make sure you understand whether you’re doing insert windows or full-frame replacement.

Product-Specific Measurement Tips

Different window treatments have unique measurement requirements:

Measuring for Horizontal Blinds

Horizontal blinds are versatile window treatments popular in Sacramento homes:

Inside Mount Requirements:

Minimum 2-inch depth from inside edge to glass
Measure jamb to jamb width at three points
The headrail requires clearance at the top inside of the frame
Account for tilt mechanisms and cord placement

Outside Mount Considerations:

Add 3-4 inches on each side of the window frame
Extend 3 inches above the window opening
Drop 3 inches below the sill or to your desired length
Ensure mounting surface can support the blind weight

Material Variations:

Wood blinds are heavier and may need reinforced mounting
Faux wood blinds offer similar appearance with lighter weight
Aluminum blinds are lightest but still need accurate measurements

Measuring for Window Shades

Shades offer diverse styles and functions:

Cellular/Honeycomb Shades:

Need 2-3 inches depth depending on cell size
Single-cell requires less depth than double-cell
Measure carefully if you have window cranks or locks
Consider how much the shade will stack when raised

Roller Shades:

Require minimal depth (about 2 inches)
Work well for both inside and outside mount
For blackout options, outside mount with adequate overlap provides best light control
Measure the opening precisely for a clean look

Roman Shades:

Create soft folds when raised
Need additional stacking space at top of window
Plan for fabric to stack 10-12 inches when fully raised
Consider the weight when selecting mounting method

Woven Wood Shades:

Typically require 2-3 inches of depth
Natural materials can vary slightly in size
Measure carefully and note any irregularities in the window opening

Measuring for Plantation Shutters

Shutters have the most demanding measurement requirements:

Depth Requirements:

Minimum 3-3.5 inches for inside mount
Measure from inside edge to glass at multiple points
Check for any window cranks or moving parts
Note the location of window locks

Frame Considerations:

Shutters can be installed inside the existing frame or with their own frame
Frame-mounted shutters are more forgiving of irregular openings
Frameless installations require very precise measurements

Panel Configuration:

Decide on bi-fold, tri-fold, or bypass panels
Consider how panels will stack when open
Measure the width and height to determine optimal panel size
For larger windows, multiple panels may be necessary

Understanding Window Replacement and Measurements

If you’re considering replacing windows along with adding new treatments, understanding the relationship between window replacement and window treatment measurements is important:

Insert Replacement Windows

Insert windows (also called replacement units) fit into the existing frame:

The new window is installed inside the old window frame
Measure the existing frame opening for the insert windows
After installation, measure the new window opening for treatments
The opening will be slightly smaller than the original

Full-Frame Replacement

A full-frame replacement removes the entire old window and frame:

The rough opening in the wall is used for the new window
New framing and casing are installed
After the replacement process is complete, measure the new frame for window treatments
This often provides a better opportunity for inside mount treatments

Coordinating Window and Treatment Installation

When you’re replacing old windows and adding new window treatments:

Complete the window replacement first
Allow the casing and trim work to be finished
Then measure for window treatments using the final dimensions
This ensures your measurements and make the most accurate template for your new blinds or shades

When to Call a Professional for Measurement

While many homeowners can successfully measure their own windows, some situations benefit from expert help:

Complex Window Configurations: Bay windows, unusual angles, or specialty shapes require experience to measure correctly and find the perfect treatment solution.

Multiple Windows Throughout Your Home: If you’re treating an entire home, a professional can ensure consistency, catch potential issues, and provide instructions to get the best results across all rooms.

Uncertainty About Product Choice: Not sure whether blinds, shades, or shutters are right for your space? Professional consultation helps you explore options and learn how to measure for each type.

Older or Historic Homes: Sacramento has many beautiful historic homes with unique window configurations. Professionals experienced with older homes can navigate challenges like uneven frames, shallow depths, or unusual dimensions.

Replacement Window Projects: If you’re also replacing windows, coordinating the replacement process with window treatment selection ensures optimal results.

Carpentry or Structural Concerns: If your windows have structural issues, damaged jambs, or need carpentry work, professionals can assess and address these before treatment installation.

The Blinds of Sacramento Advantage

At Blinds of Sacramento, we offer free in-home consultations throughout the Sacramento area. Here’s what you can expect:

Expert Measurement: We’ll measure every window accurately, accounting for all the factors that affect fit and function. We know how to measure the width, measure the height, and measure the inside dimensions precisely.

Product Recommendations: Based on your needs, style preferences, and budget, we’ll help you choose the perfect window treatment for each room.

No-Pressure Experience: We believe in educating our customers and letting them make informed decisions. There’s never any pressure to buy.

Child Safety Expertise: As a mother of three, owner Jessica Claveria prioritizes child-safe options and can guide you toward cordless and motorized solutions that eliminate hazardous cords.

Local Knowledge: With over 18 years serving Sacramento homes, we understand the unique challenges and opportunities of window treatments in our climate and architectural styles.

Expert Tips for Sacramento Homeowners

After nearly two decades of serving Sacramento homeowners, we’ve learned valuable tips on measuring windows and selecting treatments:

Sacramento Climate Considerations

Summer Heat Management: Sacramento’s hot summers make energy efficiency crucial. When measuring for outside mounts, adding extra overlap (4-5 inches per side instead of 3-4) provides better insulation and blocks more heat—an important home improvement that reduces cooling costs.

Winter Insulation: Cellular shades offer excellent insulation. For inside mounts, ensure you have adequate depth for double-cell shades, which provide superior energy efficiency during cooler months.

UV Protection: Our intense sunlight can fade furniture and flooring. When measuring for solar shades or light-filtering options, consider coverage that protects your interior while maintaining views.

Maximizing Your Home Improvement Investment

Accurate Replacement Measurements: Whether you’re doing an insert replacement or installing new treatments in existing frames, taking the time to measure the distance correctly at three different spots ensures perfect results.

Planning for Future Updates: If you’re considering replacing windows in the future, choose window treatments that can be easily adjusted or remounted after the replacement unit is installed.

Coordinating with Other Projects: If you’re planning other home improvement projects like painting or trim work, complete those before final window treatment measurements.

Knowing How to Measure

Measuring windows for blinds and shades doesn’t have to be intimidating. Here are the key takeaways:

✓ Always use a metal tape measure for accurate, consistent window measurements

✓ Measure the width and height at three points each, then use the smallest measurement for inside mounts

✓ Measure from jamb to jamb for inside mount width, recording exact dimensions

✓ Measure the distance from the head jamb to sill at three different spots for height

✓ Check depth requirements before committing to inside mount—different products need different clearances from the inside edge

✓ Decide between inside mount and outside mount based on your window frame depth, desired look, and light control needs

✓ Add adequate overlap for outside mounts—typically 3-4 inches on each side and above/below the window opening

✓ Double check all measurements and make detailed notes—location, dimensions, obstructions, and window type

✓ Measure window openings individually—don’t assume identical-looking windows have the same window size

✓ Understand the parts of a window—knowing the head jamb, side jamb, sill, and casing helps you communicate accurately

✓ Use shims if needed during installation to ensure level mounting even if the window isn’t perfectly square

✓ Consider professional help for complex situations, larger windows, replacement window coordination, or if you’re uncertain about any aspect

Remember, knowing how to measure your windows accurately is the foundation of beautiful, functional window treatments. Taking the time to measure the opening correctly now prevents costly mistakes and delays later. These simple steps ensure you find the perfect fit for your home.

DIY Measurement Approach

If you’re confident in your ability to measure a window:

Follow this step-by-step guide carefully
Measure each window at least twice to double check accuracy
Record all measurements with detailed notes about window type and location
Contact us with your measurements for a quote on the perfect blind or shade

Whether you’re looking for energy-efficient cellular shades, classic wood blinds, elegant plantation shutters, modern motorized solutions, or guidance on coordinating with window replacement, we’re here to help you find the perfect window treatment for your Sacramento home.