How to Measure for Retractable Screens Without Ordering the Wrong Size

To measure for a retractable screen, measure the opening width at the top, middle and bottom and the height at the left, center and right, then record the smallest of each. Next check the opening for plumb and square, and confirm you have enough flat mounting surface for the housing and tracks. Those six numbers plus two checks decide whether you order an inside mount, an outside mount, or need a build-out first.

This page covers hinged and sliding door openings, windows and large patio or porch openings. The principle is the same for all three; what changes is the tolerance and what you measure against. If you are still choosing between product types, start with the retractable screen guide or the screen selector. For awnings, the method is different; use how to measure for an awning instead.

What you need before you start

• A steel tape measure with a stiff blade (a 25 ft / 7.5 m tape is fine for doors; use a 30-35 ft tape or a laser distance meter for patio openings)
• A 4 ft (1.2 m) level, or a 2 ft level plus a straightedge
• A small square or combination square for checking jamb faces
• Pencil and a sketch of the opening (front view plus a plan view of the jamb)
• Painter's tape to mark measuring points so a second check uses the same spots
• The manufacturer's measuring sheet, if you already know the brand

Decide inside mount or outside mount first

Everything you measure depends on where the housing and tracks will sit. An inside mount fits between the side jambs and under the head jamb, so you measure the clear opening. An outside mount screws to the face of the trim (brickmold or casing) or the wall, so you measure the area the frame will cover and confirm the surface is flat.

When an inside mount fails the checks below, outside mount is usually the rescue, provided the trim is wide and flat enough. Brick returns, stucco and very narrow casing may need a wood build-out frame first.

How to measure, step by step

1. Clear and inspect the opening. Remove anything that will not stay: old screen door hardware, closers, storm-door Z-bars, loose weatherstrip. Note door handles, deadbolts and hinge knuckles that project into the opening, because the screen housing and handle must clear them. Measure the handle projection from the jamb face; most screen housings need the door hardware to sit at least 2-2.5 in (50-64 mm) clear of where the screen pull bar travels.
2. Measure width at three heights. For inside mount, measure jamb to jamb about 4 in (100 mm) below the head, at mid-height, and about 4 in above the threshold. Write all three down. For outside mount, measure across the trim faces at the same three heights.
3. Measure height at three points. Measure from the threshold or sill to the underside of the head jamb at the left jamb, center and right jamb. On a door, measure to the highest point of the threshold that the bottom track or sill adapter will sit on, not to the floor in front of it.
4. Record the smallest of each. Your order width is the smallest width; your order height is the smallest height. Do not round. Note the largest too, because the difference tells you how much shimming or adjustment the product must absorb.
5. Check plumb on both jambs. Hold the level against each jamb face, front to back and side to side. Record how far the top is out relative to the bottom. More than 1/8 in over 6 ft 8 in (3 mm over 2 m) is worth noting; more than 1/4 in (6 mm) usually needs shims or an outside mount.
6. Check square with diagonals. Measure corner to corner both ways. If the diagonals match within 1/4 in (6 mm), the opening is square enough for most products. A bigger difference means the opening is racked, and the screen will close tight at one corner and gap at the other.
7. Measure the mounting depth. For inside mount, measure the flat portion of each jamb from the door stop or the back of the jamb to the outside edge. Compare that with the housing depth on the spec sheet. For outside mount, measure the flat width of the casing face on each side and across the head.
8. Check the threshold or sill. Lay the level across the sill. Many door thresholds slope outward 5-8 degrees to shed water, and some have a raised bead. Note slope and any raised profile, because the bottom guide or sill adapter needs a flat landing.
9. Note the handing. Decide which side the screen housing goes on and which way it pulls. For a single hinged door, the housing usually goes on the hinge side so the pull bar latches at the handle side, but many people reverse this to keep the housing out of a traffic path. Write it down: "housing left, viewed from outside" removes ambiguity.
10. Photograph and re-measure. Take a photo of the opening with the tape visible at each measurement point. Then remeasure the smallest width and height a second time, ideally by a different person. Two people measuring independently catch most transposition mistakes.

Reading your numbers: what the spread tells you

The point of three readings is the spread between them. A perfect opening shows identical numbers; real houses settle, and doors installed over decades drift.

Measuring door openings

Hinged single and double doors are the most common case. Watch three things beyond width and height.

Door swing and handle clearance

Retractable screens mount on the opposite side of the door from where it swings. On an in-swinging entry door, the screen goes on the outside face of the jambs. Check that the screen housing and pull bar will not sit where the door's own weatherstrip, kick plate or storm-door hinge rail lives.

French and double doors

For a pair of doors, you usually order two screens that meet in the middle, or one wide screen with a single housing. Measure the full opening the same way, then check the center: if there is an astragal or a center post, note its width. See retractable screens for French doors for configuration options.

Sliding glass doors

For sliders, measure the opening the screen will cover, usually the operable panel only. Many people prefer a retractable over a standard sliding screen because it removes the bottom roller track. More on that in screens for sliding glass doors.

Measuring windows

Retractable window screens typically mount inside the window frame or on the interior trim. Measure the same three widths and heights, but also measure the clear depth between the sash (or crank operator) and the inside face of the frame, because casement cranks and tilt latches are the usual obstruction. Windows tolerate less out-of-square than doors, since the screen cassettes are lighter and less adjustable. See retractable window screens for the product side.

Measuring large patio and porch openings

Openings for motorized or large manual screens can reach 20 ft (6 m) or more, and the margin for error shrinks as width grows because a long header will sag or bow.

• Use a laser distance meter or have a helper hold the tape end. A drooping tape over 15 ft reads long.
• Measure width at the top (where the housing goes), the middle and the bottom. Posts on porches frequently lean.
• Measure height at each post and at mid-span. A header that sags 1/2 in (13 mm) at the center changes how the bottom bar lands.
• Check the floor for slope. Patio slabs are often sloped 1/8-1/4 in per ft (1-2%) away from the house, so a 12 ft deep porch can drop 1.5-3 in (38-76 mm) side to side or front to back.
• Record the header depth and what it is made of, since the housing needs solid fixing. See finding studs, rafters and blocking.
• Note where power can reach the motor end; see wiring a motorized awning for the same rules applied to screens.

For a full walk-through of mounting once you have the sizes, see installing motorized patio screens.

Frequently asked questions