How to Measure for Bathroom Tub Doors | Get the Fit Right

Measure your tub door opening from finished wall to finished wall at the top and bottom, top of the tub to finished wall height, and threshold depth front-to-back.

Getting the measurements right for bathroom tub doors is the difference between a smooth installation and a frustrating return. The good news is that it only takes a few careful measurements, a tape measure, and about ten minutes. The key is measuring the finished opening—after tile and surround are in place—not the rough framing underneath.

What You Need Before You Start Measuring

Wait until all wall surfaces are finished. Manufacturer guides consistently instruct you to measure against the final walls and surround, not the bare studs. Tile, fiberglass, and acrylic surrounds all add thickness that changes the opening dimensions.

Grab a tape measure, a pencil, and a notepad. You’ll also want a stepladder if your tub surround rises high. Write down every number as you go—don’t trust your memory.

• Measure from finished wall to finished wall (not rough framing)
• Use the smallest width measurement for fit checks
• Check the wall surfaces for plumb (level) before ordering

How Do You Measure the Width and Height?

For width, measure the opening at the top and bottom of the enclosure from finished wall surface to finished wall surface. Lowe’s recommends taking a third measurement at the midpoint and using the shortest of the three. This matters because walls are rarely perfectly plumb—the top may be wider or narrower than the bottom. Delta’s guidance states that all their tub doors handle out-of-plumb conditions up to 3/8 inch, meaning the difference between top and bottom width readings should stay under 3/8 inch. If yours exceeds that, you’ll need to address the wall alignment before shopping.

For height, the Shower Door Store guide says to measure the maximum height from the top of the tub deck or threshold straight up to the highest point of the tile or fiberglass wall. This gives the maximum door height available. The product’s spec sheet will list a finished door height and a minimum clearance height—verify your opening provides both. As an example, Delta’s product sheet for one framed door lists a 60-3/8-inch finished height with a 63-inch minimum clearance requirement, so your measured height must exceed 63 inches for that model to work.

Threshold Depth and Other Clearance Checks

Measure the sill or threshold from front to back, edge to edge. Many framed and semi-frameless systems require specific sill depths for the track to mount correctly. Delta’s example product list requires 2-1/4 inches of sill depth. The same sheet notes that studs need to be located 1-5/8 inches back from the front surface of the threshold. If you’re replacing an older door, confirm the existing sill matches your new door’s requirement.

Verify your rough opening dimensions against the product’s spec sheet before purchasing. Fit is model-specific: the opening width, height, sill depth, and plumb tolerance must all match. At our roundup of the best bathroom tub doors, each model listing highlights the fit range, so you can quickly narrow your options to models that work in your opening.

The most common mistakes are measuring before the tile is complete, using rough wall dimensions, ignoring sloped or leaning walls, and skipping the threshold depth check entirely. Any of these leads to a door that doesn’t fit or leaves gaps that leak. If your numbers fall outside a product’s listed range, don’t force it—find a model with a wider adjustment range or a custom-size option.

Measure twice, order once. Ten careful minutes with a tape measure saves hours of installation headaches and a return-shipping fee. When in doubt, contact the manufacturer with your numbers before you order; their technical teams can confirm whether your opening works with a specific model.