How to Measure for a Screen Door | Measure the Opening, Not the Door

Measure the exterior door opening at its narrowest width and shortest height, then match those numbers to the maker’s size chart before ordering.

Ordering by nominal size invites returns: a “36 × 80” door ships with a smaller frame, and your opening is rarely nominal. A five-minute tape job in three spots per direction decides whether it fits. Here’s what to measure, what makers publish, and the mounting-surface check most people skip.

What Exactly Do You Measure for a Screen Door?

Measure the opening framed by your exterior trim or brickmold, not the existing door slab. The screen or storm door hangs on the trim outside, so the trim’s inside faces define the space the frame must occupy.

Hook the tape on the inside face of one side’s exterior trim and read to the inside face of the opposite trim—at top, middle, and bottom. Out-of-square openings and tapered jambs are common on older homes, so the three numbers rarely agree; the smallest matters.

For height, run the tape at the center from the underside of the upper exterior trim to the top of the sill. Record the shortest usable height where the manufacturer asks for more than one vertical reading.

Everything in inches, no rounding up on a borderline result. A measurement of 35 7/8 inches is 35 7/8 inches; rounding to 36 can put you outside the chart.

How Do Manufacturer Size Charts Compare?

Allowances differ by brand and series, and the smallest numbers decide what fits. Andersen’s storm-door documentation organizes opening ranges by nominal size and product line, and ranges aren’t identical across lines.

Note the low end: the 2000/400 and EMCO lines accept openings roughly an eighth of an inch narrower than the 3000/4000 lines at the same nominal size. A 31 3/4-inch opening fits the second group and misses the first. Height holds at 80 to 80 7/8 inches across these charts.

Andersen’s figures come from its standard and custom storm-door size charts; openings outside those ranges need a custom-size door where the line offers one.

Retractable screens run their own charts. An Andersen retractable insect-screen guide lists a 36-inch configuration at 34 to 36 3/8 inches wide, with heights of 80–80 7/8, 78–78 7/8, or 84–84 7/8 inches depending on configuration. Those numbers belong to that product alone.

What Mounting Surface Do You Need Before Ordering?

A correct tape measurement still fails if the trim can’t hold the frame. Both makers publish minimum flat-surface requirements, and depth trips up more buyers than width.

LARSON’s official measuring page calls for a 1-inch-wide by 1-inch-deep mounting surface, notes hinge-side shimming may be needed, and that shims aren’t included. Andersen specifies 1 inch depth, 3/4 inch front flat width, and 2 1/2 inches handle clearance, with its brochure citing 2 1/2 inches jamb depth and a caution that handle geometry can demand more.

Walk the trim with a straightedge. Soft or rotted wood, a hard-sloping sill, or an existing bolted storm-door frame all change the plan. Andersen’s guide to adjusting exterior trim mounting surfaces covers what the trim needs before install.

Handing matters too: Andersen’s 3000 and 4000 Series doors with the 45-Minute Easy Install System require specifying hinge side at purchase, so note the swing direction before checkout. To compare models first, this roundup of tested screen doors worth buying lays out options alongside their sizing ranges.

Which Measurement Mistakes Cause Returns?

• Measuring the old door slab. Tells you nothing about the trim opening.
• One width reading only. A tapered opening goes unnoticed until the frame sits crooked.
• Measuring from the wrong trim edge. Use the inside face of the exterior trim or brickmold.
• Treating 36 × 80 as the frame size. The frame is smaller; the chart allows for it.
• Assuming one chart covers every line. Series and product type change the numbers.

One margin call: if your narrowest width or shortest height lands outside the chart by a hair, call the manufacturer or dealer before ordering rather than assuming it will squeeze in.