How to Measure a Storm Door Opening Before Choosing a Door

Storm Door Buying and Fit

To measure a storm door opening, measure the width between the inside faces of the exterior trim at the top, middle, and bottom. Keep all three readings and identify the narrowest. Measure the height from the sill to the underside of the top trim. Andersen’s measuring instructions use these reference points, then match the opening to the selected model.[6]

That gives you a starting set of dimensions, not permission to order any door with a similar size on the box. Trim width, mounting depth, and handle clearance need their own checks. This guide helps you record those details without confusing the existing door panel with the opening that will receive the new frame.

For the broader choice of glass, screens, and features, use our storm door buying guide. Here, the task is to make a useful measurement sheet and identify what still needs verification.

Identify the opening before using the tape

Look at the doorway from outside. Find the exterior trim around the entry, often called brickmould, and the sill at the bottom. Andersen measures width at the inside faces of that exterior trim and height from the sill to the underside of the brickmould above.[6] Measuring across the movable entry-door panel is a different measurement.

If an old storm door covers those reference points, mark that on your notes. Do not label a reading taken between the old metal rails as a confirmed measurement of the trim opening. Leave concealed dimensions unresolved rather than removing hardware simply to finish this checklist. Our storm door replacement page explains why the condition behind an existing unit needs review.

Use a tape with readable inch and fractional-inch marks, and write down each reading as you take it. Larson’s tape-measure guide explains the half-, quarter-, eighth-, and sixteenth-inch marks.[14] Keep the fractions you observe instead of rounding the opening to a familiar door size. Label the units so a later reader does not have to guess.

Record three widths, not one average

Larson and Andersen both direct homeowners to measure across the opening at the top, middle, and bottom and use the narrowest measurement.[14][6] Keep the tape running across the same reference surfaces at each position.

1. Write the top width with its fraction.
2. Move to the middle and record a separate width.
3. Record the bottom width.
4. Circle the smallest reading while leaving the other two visible.

Do not average the readings or replace them with the size printed on the old door. If one reading looks unexpected, repeat it from the same reference points. If it still differs, keep the difference in your notes and ask for an opening review. A neat-looking single number is less useful than an honest record of what you measured.

Measure height at the mounting opening

For Andersen’s illustrated measurement, start at the sill and measure vertically to the underside of the brickmould at the top.[6] Larson’s universal-hinged fullview installation overview describes measuring from the threshold where the storm door will sit to the top.[15] Use the diagram for the product being considered to confirm the endpoints.

Write down where you placed the tape. If the sill slopes or the old frame prevents a clear reading, describe that condition instead of quietly choosing a different starting point. You can record additional left and right readings as observations for the installer, but do not substitute a homemade sizing rule for the selected manufacturer’s instructions.

This is also the time to note anything you could not reach or identify reliably. A measurement marked “approximate, old frame still installed” tells the person reviewing the project far more than an unexplained number.

Keep trim width and depth separate from door width

The opening dimension and the available mounting surface are different checks. Andersen’s current guide lists a minimum three-quarter-inch flat trim width, one-inch trim depth, and two-and-a-half-inch jamb depth. It warns that the entry handle’s depth and location may require additional clearance.[6]

Larson’s overview for a universal-hinged fullview storm door specifies a mounting surface one inch wide by one inch deep.[15] These are attributed examples from different instructions, not a single rule for every storm door. Record the product name beside the requirements you are checking, and confirm the current manual before purchase.

Do not assume decorative trim provides the required flat area just because its overall width is large. Mark an uncertain mounting face for review. Storm Doors Galore’s installation service considers the opening, brickmould, trim condition, sill, swing, and handle clearance when defining the work.[11]

Check square and handle space without changing the opening

In its universal-hinged fullview overview, Larson calls for diagonal readings in both directions and says they should be within one-eighth inch of each other.[15] That tolerance belongs to the installation described there. It is not a universal acceptance test for Andersen, ProVia, or every Larson model.

If you record diagonals, label the endpoints and keep both readings. Ask the installer to interpret a difference against the actual mounting system. Do not begin cutting trim or adding shims from this preliminary worksheet.

Next, look at the existing entry handle from the side with the main door closed. Note a projecting lever, knob, or deadbolt and any current contact with the storm door. Andersen’s clearance warning means that meeting its listed jamb depth alone does not settle handle fit.[6] The proposed storm door hardware still needs to be checked against the existing hardware.

Record the preferred hinge side as viewed from outside, along with nearby walls, steps, or railings you want reviewed. Leave an uncertain swing marked as a question. Selecting the door’s appearance can wait until those fit questions have answers.

Copy this measurement sheet for your estimate

Keep the observations and the ordering decision separate. Use these labels in your project notes:

• Project city, ZIP code, and entry location.
• Existing storm door present: yes or no.
• Width at top, middle, and bottom, with the narrowest identified.
• Height and the exact sill and top-trim reference points used.
• Available flat trim width, trim depth, and jamb depth, where measurable.
• Diagonal readings, if taken, labeled by direction.
• Handle projection or contact concerns and preferred hinge side.
• Manufacturer, exact model, and the measuring instructions consulted.
• Concealed, approximate, or uncertain measurements requiring confirmation.

Compare the completed sheet with the opening range for the selected model, not a generic nominal size. Andersen explicitly bases door sizing on both the opening measurements and the model selected.[6] If a dimension falls outside the applicable range, stop at the question rather than choosing the closest size yourself.

Storm Doors Galore installs ProVia, Larson, and Andersen doors in Columbus, Delaware, Sunbury, Pickerington, and Grove City, Ohio. Paul purchases project materials after the product and scope are approved.[11] Include your preliminary measurements in the quote request and ask what must be confirmed before that purchase.

If photos are requested, use the private online upload process supplied for your project.[12] Prepare views of the full opening, sill, trim, and handle area. The Central Ohio installation guide covers the rest of the project planning, and our door guides library collects related buying and replacement advice.