Blind Size Calculator

About the Blind Size Calculator

Ordering custom blinds or shades with the wrong measurements is an expensive mistake - most custom window treatments aren't returnable. The difference between inside and outside mount sizing, combined with the precise deductions and additions required, trips up even experienced homeowners. A small measurement error can also change how well the blind blocks light or clears the frame. That is why it helps to convert measurements into order dimensions before you buy.

This blind size calculator converts your raw window measurements into exact ordering dimensions for both inside and outside mounts. It handles the standard deductions (1/4" for inside mounts) and additions (3" per side for outside mounts) automatically, checks whether your window frame has enough depth for your chosen blind type, and estimates costs across six popular blind styles.

Whether you're outfitting a single window or an entire house, the calculator helps you determine the right type, confirm proper measurements, and budget accurately before placing your order.

When This Page Helps

Use this calculator to turn window measurements into order dimensions that actually fit the frame and the mounting style you want. It is useful when you need to compare inside and outside mounts, check depth requirements, and estimate costs before ordering custom blinds or shades. That makes it easier to avoid a wrong-size order before you spend money on custom treatments.

How to Use the Inputs

1. Measure your window opening width and height in inches (measure at 3 points and use the smallest)
2. Measure the depth of your window frame for inside mount compatibility
3. Enter the number of windows to outfit
4. Select inside mount (cleaner look) or outside mount (better light blocking)
5. Choose your preferred blind type from the dropdown
6. Review the order dimensions, cost estimate, and depth check
7. Compare blind types in the cost comparison table

Example Calculation

Tips & Best Practices

• Always measure each window individually — even windows that look identical can vary by 1/2" or more
• Use a steel tape measure for precision; cloth tapes stretch and give inaccurate readings
• For inside mount, measure at three points (top/middle/bottom for width, left/center/right for height)
• Use the smallest width and largest height from your measurements
• Outside mount should overlap the window opening by at least 3" on each side for proper light blocking

Choosing Between Inside and Outside Mount

Inside mount provides a clean, built-in look that works beautifully with decorative window trim. The blind fits flush within the frame, leaving the trim visible. However, it requires minimum frame depth (varies by blind type) and provides less complete light blocking since small gaps exist at the edges. Outside mount is the better choice for shallow frames, maximum light blocking, and making windows appear larger — the blind covers the entire frame plus wall overlap.

Popular Blind Types Compared

Cellular shades offer the best energy efficiency with their honeycomb air pockets. Venetian blinds provide the most adjustable light control with tiltable slats. Roller shades are the most affordable and streamlined. Wood and faux wood blinds add warmth and texture. Roman shades offer a soft, fabric look ideal for formal spaces. Vertical blinds are the standard for sliding doors and very wide windows.

Common Measurement Mistakes

The number one mistake is measuring once and assuming all windows are identical. Windows in the same room can vary by 1/2 inch or more due to settling, construction tolerances, and humidity changes. Other common errors include measuring at only one point (instead of three), not checking frame depth before ordering inside mount blinds, and forgetting to account for handles, cranks, or sensors that might interfere with blind operation.

Frequently Asked Questions

• What's the difference between inside and outside mount?

  Inside mount fits within the window frame for a clean, built-in look. Outside mount attaches to the wall above the frame, covering more area and blocking more light. Inside mount requires sufficient frame depth (usually 2-3").

• How do I measure for inside mount blinds?

  Measure width at top, middle, and bottom of the window opening. Use the narrowest measurement. Measure height on left, center, and right. Use the longest measurement. Most manufacturers want exact measurements — they'll apply deductions.

• How much depth do I need for inside mount?

  It varies by blind type: roller shades need 1.5", cellular shades 2", venetian blinds 2.5", and wood blinds 2.75". If your frame is too shallow, use outside mount instead.

• Should I round up or down on measurements?

  For inside mount, measure precisely to the nearest 1/8 inch — don't round up or the blinds won't fit. For outside mount, it's safer to add a bit extra since the blind sits on the wall outside the frame.

• Which blind type is most energy efficient?

  Cellular (honeycomb) shades are the most energy efficient, with their air-trapping honeycomb structure providing R-values of 2-5. They can reduce heat loss through windows by 40-50% compared to unshaded windows.

• Can I install blinds myself?

  Yes, most blinds come with installation hardware and instructions. Inside mount blinds are generally easier — just screw brackets into the top of the window frame. Outside mount requires drilling into the wall and may need anchors.