How to Measure Arched and Oversized Window Screens

To measure an arched or oversized window screen, measure the rectangular portion at three points for width and three for height using the smallest reading, then make a physical paper template of the arch — never try to calculate a curve from a radius. The three-point rule catches out-of-square openings, and the template captures curves that no set of numbers describes reliably.

That second point is where most DIY orders fail. Arches in Valley homes are frequently not true half-circles, and a screen cut to a mathematically perfect arc won't seat in an opening that isn't one.

What You Need

• A steel tape measure (not a cloth or flexible one — they stretch)
• Butcher paper, kraft paper, or taped-together poster board for templates
• A pencil and a marker
• Painter's tape
• A helper for anything over about six feet
• A notepad or phone to record every measurement immediately

Step 1: Decide What You're Measuring To

Before any tape touches the wall, identify the screen's mounting type, because it changes what surface you measure to:

• Channel or track mount — the screen sits inside a groove in the window frame. Measure inside the channel, groove to groove.
• Surface mount with clips — the screen sits on the face of the frame. Measure the frame face dimensions.
• Tension or spring-loaded — measure the tight opening; the screen needs to compress into it.

Getting this wrong is the most common single cause of a screen arriving the wrong size. If you're unsure which you have, photograph the existing screen edge and the window frame and ask before ordering.

Step 2: Measure Width at Three Heights

Measure the width at the top, middle, and bottom of the opening. Record all three. Use the smallest measurement.

On a truly square opening, all three will match. In practice, especially in older Valley homes and in stucco construction where settling is common, they often vary by a quarter inch or more. If you use the largest, the screen won't fit at the narrow point. If you use the smallest, it fits everywhere.

Step 3: Measure Height at Three Widths

Same method: measure the height at the left, center, and right of the opening. Record all three. Use the smallest.

For an arched window, this height measurement applies only to the rectangular portion below the spring line — the point where the arch begins. Measure from the sill up to the spring line, not up to the peak of the arch.

Step 4: Check for Square

Measure both diagonals, corner to corner. If they differ by more than about an eighth of an inch, the opening isn't square, and a standard rectangular screen will show a visible gap on one side.

Record the diagonal difference. A fabricator can build a slightly trapezoidal screen to match, but only if they know.

Step 5: Template the Arch

This is the part that can't be skipped.

1. Tape butcher paper across the entire arched portion of the opening, from spring line to peak, extending well past the edges.
2. With a pencil held flat against the frame, trace the inside edge of the opening — the exact line where the screen needs to sit. Keep the pencil tight to the frame the whole way around.
3. Mark the spring line on both sides with a heavy line, and label the top edge TOP and one side LEFT (facing from inside).
4. Remove the paper, cut along your traced line, and hold the cut template back up to the window. It should sit within the opening cleanly. If it's off anywhere, re-trace that section.
5. Write the window's location on the template — "master bath, east wall" — in marker.

Do not try to substitute a radius measurement for a template. Eyebrow arches, elliptical arches, and segmental arches are all common in Phoenix-area homes, and none of them are half-circles.

Step 6: Handle Oversized Openings

For windows over roughly six feet in any direction, a few extra rules apply:

• Use two people. A tape measure sags over long spans and reads long. One person holds the hook, the other reads at the frame.
• Measure at the frame, not by eye from a distance. On a tall window, use a ladder rather than estimating.
• Ask about a center brace. Large screens flex and bow, especially in monsoon wind. Most fabricators add a horizontal crossbar above a certain size — confirm whether yours will, and where it will sit, since it's visible.
• Consider splitting into two panels. On very wide openings, two screens are often more practical to handle, install, and replace than one oversized panel.
• Check the mesh width limit. Screen mesh comes in standard roll widths. If your opening exceeds the widest available roll, the screen needs a seam or a split panel.

Step 7: Record and Label Everything

For each window, write down:

1. Room and wall location
2. Mount type
3. All three width readings, with the smallest circled
4. All three height readings, with the smallest circled
5. Both diagonals
6. Whether a template exists for this window
7. A photo of the opening and the existing screen edge

A labeled set of measurements and templates is what turns a complicated whole-house order into a single accurate build.

Common Mistakes

• Measuring the old screen instead of the opening. If the old screen was wrong, you've just reordered the same mistake.
• Rounding to the nearest inch. Measure to the nearest sixteenth.
• Forgetting to subtract for clearance. Most fabricators apply their own clearance deduction — give them the raw opening measurement and let them handle it. Deducting yourself and having them deduct again produces a screen that's too small.
• Measuring one arch and assuming the rest match. Template every arch individually, even in a matched set.
• Using a cloth tape. It stretches. Steel only.

When to Let Someone Else Measure

Be honest about the risk. If an arched or oversized screen comes back wrong, it's a custom piece — there's no returning it. For a single standard rectangular window, DIY measuring is straightforward. For arches, two-story windows, out-of-square openings, or a whole-house order, having it measured professionally is usually the cheaper path once you account for the cost of a remake.

Window Screen Guys offers both. If you want to measure yourself, order through Screens2Go and we'll fabricate to your numbers and deliver on our Valley-wide routes. If you'd rather we measure, we'll come out, template every arch, and install the finished screens; a measuring fee applies on measure-and-deliver orders and is quoted up front.

Get It Measured Right

Window Screen Guys custom-builds screens for arched, oversized, and nonstandard windows across Phoenix, Scottsdale, Peoria, Surprise, Glendale, Cave Creek, Anthem, and North Phoenix. Licensed Arizona contractor, ROC #362719.

Call (480) 771-6091 or request a free quote.

Frequently Asked Questions

How do you measure an arched window for a custom screen?

Measure the rectangular portion below the spring line using the three-point method for width and height, take both diagonals to check square, then make a physical paper template of the arch by taping paper over the opening and tracing the inside edge of the frame. The template is essential — arches in most homes are not true half-circles, so a calculated radius won't match the actual opening.

Should I measure the window opening or the existing screen?

Always measure the opening. Measuring the existing screen reproduces any sizing error it already has, which is common on resale homes and on screens a previous owner bought in standard sizes. The opening is the only reliable reference.

Why do I need three measurements for width and height?

Because openings are rarely perfectly square. Settling, stucco construction, and age all cause variation, and three readings reveal it. Using the smallest of the three ensures the screen fits at the tightest point rather than binding partway in.

Do I need to subtract for clearance when measuring screens?

No — give the fabricator the raw opening measurement. Most shops apply their own clearance deduction based on the mount type and frame profile. If you deduct as well, the deduction gets applied twice and the screen comes back undersized with visible gaps.

Can very large window screens be made in one piece?

Up to a point. Screen mesh comes in standard roll widths, so an opening wider than the widest roll requires a seam or a split into two panels. Large screens also flex in monsoon wind, so a horizontal center brace is common above a certain size. On very wide openings, two panels are often easier to handle and replace than one oversized screen.