Measure from the finished tub threshold to the finished wall top, and check the width at both top and bottom.
The golden rule: measure only after the tile, grout, and surround are complete. Get the height and width right, and your new door will seal properly and slide smoothly. Here’s the step-by-step for measuring a bathtub opening the right way.
Why Measure Only the Finished Opening?
Bathroom tub doors mount onto the finished surfaces of your tub and walls. Measuring before tile or an acrylic surround is installed gives you numbers for a rough opening that no longer exists once the walls are finished. Wait until the surround is fully set, with all adhesive and grout cured, before you take your tape measure out. The width you record needs to match the final surface where the door’s tracks and walls will rest.
How to Measure the Opening Height and Width
Your key measurements are the vertical height and horizontal width of the finished opening.
- Height: Run the tape from the top edge of the tub threshold (the flat deck) straight up to where the glass will top out — which is usually the top of the acrylic surround or finished tile wall.
- Width at the top: Measure across the opening from one finished wall to the other, at the top of the opening.
- Width at the bottom: Measure across the opening at the level of the tub deck, where the bottom track will sit.
- Width in the middle: Some homeowners add this third reading for extra confidence when walls feel slightly irregular.
Compare the top and bottom widths. The difference reveals whether your walls are plumb. If the gap is larger, a different size range or a custom configuration may be necessary.
Check Threshold Depth, Plumb, and Level
Beyond opening height and width, two more checks keep your door hardware fitting cleanly. First, the threshold depth. Measure the base from front to back, edge to edge, to confirm there’s enough flat surface for the bottom track and its seal. Second, grab a level. Run it along the tub edge and hold it against the side walls. Even a slightly sloped deck can stress the glass once the door is hung, so knowing the surfaces are even matters as much as the opening’s dimensions.
A quality roundup of well-reviewed bathroom tub doors like ours lists models with clear size specifications to compare against your numbers.
Common Measuring Mistakes to Skip
- Measuring before the tiling or surround is complete, so the opening is still rough.
- Using a single width reading instead of top and bottom points. Unlevel walls get skipped this way.
- Measuring from the outside of the tub lip instead of the finished deck surface where the track will sit.
- Not checking where the glass will terminate. The height depends on where the door ends, whether that’s below the ceiling or at a surround’s top edge.
- Overlooking the depth of the threshold, which affects whether the hardware and seals fit flush.
Delta’s tub door measuring guide underlines using the finished opening and recommends taking the width at multiple points to catch out-of-square walls before you order.
With the opening height, width, and depth on paper — and your plumb check done — you can order with confidence or compare models side by side in our guide to the best tub doors available now.
References & Sources
- Delta Faucet. “Measuring & Tool Guides for Shower Doors.” Details measuring from finished surfaces, checking width at multiple points, and accounting for out-of-plumb conditions.
