How to Measure the Gap Under a Shower Door
Quick answer
Close and latch the door, then measure from the bare glass bottom edge straight down to the threshold — at the hinge end AND the handle end. Remove or push aside the old worn sweep first. Keep the larger of the two readings and buy a sweep whose wipe is 1/8 to 1/4 inch taller than it, so the vinyl flexes against the threshold instead of hovering above it.
Last updated: · Data reviewed: · Source: Prime-Line product specifications
Why “door closed, both ends” matters
Two things quietly falsify this measurement. Pivot doors ride upward slightly through their swing, so an open-door reading runs up to 1/4 in large. And frameless doors sag over years as hinge screws settle, so the gap at the handle end is often bigger than at the hinge end — a difference over 1/8 in means the door needs re-squaring before any sweep can seal it evenly.
What you need
- Tape measure or a steel rule with 1/16 in marks
- Utility knife or flat screwdriver to lift the old sweep clear
- Painter's tape and a pencil to record both readings
- A helper to hold the door firmly closed (optional but useful)
Step by step
- Clear the old sweep. Slide or peel the worn sweep off the bottom edge, or at least lift its wipe out of the way. You need bare glass to threshold — old vinyl in the measurement understates the gap.
- Close and latch the door. Fully closed, magnet engaged if there is one. Have a helper hold it if the door drifts.
- Measure the hinge end. Set the rule on the threshold directly below the glass and read up to the bare bottom edge. Note it to the nearest 1/16 in.
- Measure the handle end. Repeat at the opposite end. A difference up to 1/8 in is normal settling; more than that is hinge sag — adjust the hinges, then re-measure.
- Check the threshold slope. Lay the rule flat along the curb. If it rocks or daylight shows, note where — a sloped curb argues for the taller of two candidate wipes.
- Apply the sizing rule. Take the LARGER gap reading and add 1/8–1/4 in: that is your wipe height. A 1/4 in gap wants a 1/2 in wipe; a 1/2 in gap wants a 3/4 in wipe.
Wipe height cheat sheet
| Measured gap | Buy this wipe | Why |
|---|---|---|
| 1/16–1/4 in | 1/4 or 3/8 in wipe | Low-profile fin avoids drag on tight gaps |
| 1/8–3/8 in | 1/2 in wipe | The standard frameless size |
| 3/8–5/8 in | 3/4 in wipe | Handles gaps that vary end to end |
| 5/8–7/8 in | 1 in wipe (extra tall) | Check the listing states the wipe height |
| 7/8–1 1/8 in | 1 1/4 in wipe — or fix the door | Adjust hinges or add a threshold first |
Mistakes to avoid
- Measuring with the door open — pivot doors read up to 1/4 in large.
- Measuring from the bottom of the old worn wipe instead of bare glass.
- Taking one reading in the middle and calling it done.
- Buying a wipe exactly equal to the gap: zero overlap means zero seal.
- Sizing a sweep to hide hinge sag — it drags at one end and gaps at the other.
Frequently asked questions
What is a normal gap under a shower door?
Installers typically leave 3/16 to 1/2 inch for clearance over the curb, then close it with a sweep. It only becomes a problem when the wipe no longer spans it.
My gap is different at each end — which number do I use?
Size the wipe to the larger reading if the difference is 1/8 inch or less. Beyond that, re-square the door on its hinges first; a sweep cannot fix geometry.
Do I include the old sweep in the measurement?
No. Measure bare glass edge to threshold. The old wipe subtracts from the true gap and leads to a wipe one size too short.
Does the wipe height depend on my glass thickness?
No — thickness picks the channel that grips the glass; the gap picks the wipe hanging below it. You need both numbers, and they are independent.