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Free Blind Size calculator

Get the exact width and height to order for inside or outside mount window blinds.

On this page10 sections

InputsLive

Mount type

Window width

Window height

Result

Blind width

35 3/4 in

Height: 48 in

Width to order35 3/4 in

Height to order48 in

Mount typeInside mount

Width adjustment−1/4 in clearance

Inside mount: width is deducted 1/4 in for clearance. Order to these exact dimensions — the blind hangs inside the window frame.

Measurements are estimates based on standard inside/outside mount guidelines. Always measure your window twice before ordering and confirm sizing with your blind manufacturer's measuring guide.

Results are estimates. Consult a professional.

How it's calculated

How the blind size calculator works

The calculator takes your window measurements and mount type, then applies the standard clearance or overlap adjustments used by blind manufacturers. For an inside mount, it deducts 1/4 inch from the width so the blind slides freely without binding against the frame. For an outside mount, it adds 3 inches on each side (6 inches total) and 2 inches above the frame so the blind fully covers the window opening.

Inside mount: blind width = window width − 1/4 in

Inside mount: blind height = window height

Outside mount: blind width = window width + 6 in (3 in each side)

Outside mount: blind height = window height + 2 in + extra drop

Inside-mount deduction and outside-mount overlap guidelines follow Hunter Douglas, Budget Blinds, and IBMA (International Blind Manufacturers Association) published measuring standards.

Mount types

Inside mount vs outside mount: which to choose

The mount type is the most important decision you make before measuring. It determines how the blind attaches to the window and what measurements you take. Choose the wrong type and your blind will either not fit or leave visible gaps.

Feature	Inside mount	Outside mount
Blind hangs	Inside the window frame	On the wall or casing above the frame
Requires	Minimum 1 1/2 in frame depth for hardware	Flat wall surface above frame
Look	Clean, recessed, shows frame/sill	Larger, hides frame; makes window appear taller
Light control	Small gaps at edges are normal	Full coverage possible with wide overlap
Width adjustment	Deduct 1/4 in for clearance	Add 3 in per side (6 in total)
Best for	Deep frames, modern look	Shallow frames, privacy, light blocking

Most wood and faux-wood blinds, cellular shades, and roller shades work well either way — the frame depth and your aesthetic preference usually decide the mount.

If your window frame is shallower than about 1 1/2 inches, the mounting brackets will not have enough room to attach flush — use an outside mount. Check the minimum depth specification in your blind's installation instructions.

Step by step

How to measure a window for blinds

Accurate measurement is the difference between blinds that fit and a return shipping label. Two minutes with a steel tape measure prevents most mistakes.

Measure inside a frame (inside mount)

Measure the inside width at three heights — top, middle, and bottom of the window opening. Windows often warp slightly, so record the narrowest measurement and use that number. Then measure the inside height at three widths — left, center, and right — and use the longest measurement. Enter both numbers exactly as measured; the calculator applies the 1/4-inch width deduction.

Measure for an outside mount

Decide how high above the frame the blind will hang — 2 inches is the standard, which the calculator adds automatically. Measure the window frame width from outside edge to outside edge. For the height, measure from where the top of the blind will sit down to where you want the blind to end: either the sill or below it for a privacy overlap. Enter the window frame width and height; the calculator adds the overlap.

Always use a steel tape measure, not a fabric tape. Measure to the nearest 1/8 inch — that is the standard fraction used on blind order forms. Most manufacturers will not accept orders in finer increments than 1/8 inch.

Example

Worked example: measuring a 36 × 48 inch window

Example: a standard bedroom window, inside mount

Amara has a bedroom window with an inside frame width of 36 in and a height of 48 in. She wants a clean inside-mount roller shade.

Step 1 — Apply the width deduction

Inside mount: 36 − 0.25 = 35 3/4 in width.

Step 2 — Keep the height as measured

Height stays at 48 in — no adjustment for inside mount height.

Order: 35 3/4 in wide × 48 in tall

The 1/4-inch clearance on the width lets the blind slide smoothly without catching. The 36-inch opening appears full because the blind's face rail is wider than the deducted bracket width.

Outside mount alternative

If Amara chose an outside mount on the same window: 36 + 6 = 42 in wide; 48 + 2 = 50 in tall (with no extra drop below sill). The larger blind fully covers the frame and a few inches of wall on each side.

Quick reference

Common window blind sizes at a glance

Standard window sizes in US homes cluster around a few common widths and heights. This chart gives the inside-mount and outside-mount order dimensions for the most common window sizes, assuming no extra outside drop.

Window size	Inside mount (W × H)	Outside mount (W × H)
24 × 36 in	23 3/4 × 36 in	30 × 38 in
30 × 48 in	29 3/4 × 48 in	36 × 50 in
36 × 48 in	35 3/4 × 48 in	42 × 50 in
36 × 60 in	35 3/4 × 60 in	42 × 62 in
48 × 60 in	47 3/4 × 60 in	54 × 62 in
60 × 72 in	59 3/4 × 72 in	66 × 74 in

Inside mount deducts 1/4 in width only. Outside mount adds 6 in to width and 2 in to height with no extra drop. Always measure your specific window — these are planning figures only.

Definitions

Blind sizing definitions

A blind hung inside the window frame recess. Requires minimum frame depth for mounting hardware (typically 1 1/2 in); width is deducted 1/4 in for clearance.

A blind hung on the wall or window casing above the frame. Covers the entire window opening plus an overlap on each side and above; eliminates the need for frame depth.

The 1/4-inch reduction applied to inside-mount width so the blind can move without binding against the side jambs. The blind's face rail will appear close to full width — the brackets sit inside this deduction.

The small space between the edge of an inside-mount blind and the window frame. Inherent to inside mounting; light and visibility are greatest at the edges. For full blackout, use an outside mount with enough overlap.

The vertical space the blind occupies above the window opening when fully raised. Important for windows near the ceiling — ensure the raised blind does not block the opening. Usually 8–12% of the blind's total drop height.

Accuracy

How accurate is this blind size calculator?

The width and height formulas are industry-standard adjustments used by major blind manufacturers. The 1/4-inch inside-mount deduction and the 3-inch-per-side outside-mount overlap are the conventional starting points. If you measure accurately to the nearest 1/8 inch, the results match what you would get from a manufacturer's measuring guide.

Some manufacturers use a slightly different deduction — typically between 1/4 and 1/2 inch — so check the specific guide for the product you are ordering. Also note that specialty windows (skylights, bay windows, arched windows) may need custom measurement approaches not covered here. When ordering custom blinds, the manufacturer's measurement guarantee is only valid if you follow their exact instructions.

Questions

Frequently asked questions about the free Blind Size calculator

A blind Size calculator is a free online tool that helps you size window blinds (inside or outside mount) from your window measurements. Blinds are ordered slightly smaller (inside mount) or slightly larger (outside mount) than the raw window opening. Apply the standard deductions or additions before placing your order. It runs entirely in your browser with instant results and no sign-up.

For inside mount, measure the inside width at the top, middle, and bottom of the frame opening — use the narrowest measurement. Measure the height at three widths and use the shortest. For outside mount, measure the width you want to cover (frame plus 3 in each side) and the height from where the blind will hang to the sill or floor.

When ordering an inside-mount blind, you deduct 1/4 inch from your measured window width before ordering. This clearance gap lets the headrail slide smoothly inside the frame without binding against the side jambs. Some manufacturers apply this deduction automatically — check their guide before subtracting it yourself.

The standard is 3 inches past each side of the frame (6 inches total added to width) and 2 inches above the top of the frame. This overlap blocks the light gaps that appear around the edges of inside-mount blinds. For maximum blackout, extend even further — 4 to 6 inches per side is common in bedrooms.

Inside mount looks clean and architectural — the blind sits flush in the frame and shows the window trim. It requires a frame recess of at least 1 3/4 inches for most headrails. Outside mount is better for light blocking, shallow recesses, or when you want the window to appear larger. Both mount types work with most blind styles.

For inside mount, order 35 3/4 inches wide (36 minus 1/4 in). For outside mount, order 42 inches wide (36 plus 6 in). The height follows the same rule: inside mount orders to the window height, outside mount adds 2 inches (plus any extra drop you want below the sill).