How to Measure Windows for Exterior Shutters

Quick Answer: Exterior shutters should be sized to match the visible height of the window (from the top of the trim to the sill) and half the visible window width. This way, if the shutters were operable, they could fold closed and cover the window exactly. Getting this proportion right is the most important factor in shutters that look intentional rather than decorative afterthoughts.

Nothing undermines curb appeal faster than exterior shutters that are the wrong size. Too narrow and they look like thin strips stuck to the wall; too short and they appear to float awkwardly beside the window. Getting the sizing right is simple once you understand the underlying logic. Here is how to measure accurately for your exterior wood shutters.

The Core Sizing Rule

Shutters are traditionally operable - they were designed to fold closed over the window for weather protection and privacy. Even though modern exterior shutters are almost always fixed and decorative, they should still be sized as if they could close. That means:

• Height: Equal to the height of the visible window opening (top of trim to sill, or sill to top of window casing depending on your trim style)
• Width: Each shutter panel should be half the visible window width

A window that is 36 inches wide and 60 inches tall needs two shutter panels, each 18 inches wide and 60 inches tall.

What to Measure: Step by Step

Measuring height: Measure from the top of the window casing (the horizontal trim piece at the very top of the window) down to the bottom of the sill. This is your shutter height. If your window does not have a sill or the trim is minimal, measure to the bottom of the window frame.

Measuring width: Measure the visible window opening width - the glass width plus any interior frame visible from outside. Do not include the side casings (the vertical trim pieces on either side). Divide this number by 2 for each panel width. Round to the nearest inch.

Accounting for Trim Style

Different window trim styles affect how you measure:

• Window with full surround trim: Measure inside the trim on all four sides - height from top casing to sill, width from one side casing to the other
• Window with sill only (no head casing): Measure from the top of the window frame to the bottom of the sill
• Window with no trim: Measure the visible glass area only

When in doubt, err toward measuring the glass plus a small margin rather than including all the trim. Shutters that extend slightly beyond the glass look intentional; shutters that land in the middle of the trim look like a measuring error.

Double Windows and Wide Openings

For double-hung windows side by side with no mullion between them, treat the pair as one unit: measure the total combined width and divide by 2 for each panel. For very wide windows (48 inches or more), you may want to use four shutter panels instead of two - this looks more proportional and more traditional.

Mounting Position

Shutters typically mount directly to the siding on either side of the window casing, with about a 1/2-inch gap between the shutter edge and the window trim. This gap prevents moisture from being trapped between the shutter and the trim. Use this measurement to confirm there is enough wall space on each side to mount the shutter without overlapping adjacent windows, trim, or corners.

Standard Shutter Widths

Most exterior shutters are available in standard widths from 12 to 20 inches. If your calculated panel width does not match a standard size, round to the nearest available option or choose a manufacturer that offers custom sizing. A 1 to 2-inch difference from the exact measurement is usually visually acceptable; more than that and the proportions will read as wrong.

Quick Reference by Window Width

Browse Dogberry Collections' exterior wood shutters in board and batten, horizontal slat, X-brace, and Z-brace styles. Available in multiple standard widths and painted or stained finishes. Questions about sizing for your windows? Call us at (435) 923-4100 - Mon-Fri, 8am-4pm MT.