How to Measure Your Segment Height (SH)
Segment height refers to the vertical distance from the bottom of your lens to your pupil. When measured correctly, progressive, bifocal, and multifocal lenses align exactly where you need them for smooth, comfortable vision.
WHAT IS SEGMENT HEIGHT?
Segment height (SH) is the measurement from the bottom edge of your eyeglass lens up to the pupil center (for progressive lenses) or the lower eyelid (for bifocals). This measurement ensures the near and intermediate viewing zones sit in the correct position for your natural line of sight.
BEFORE YOU BEGIN
- Wear the exact frame you plan to order lenses for.
- If ordering new glasses, use frames with a similar lens height as your intended pair.
- Stand in bright, even lighting and face forward.
- Use a millimeter ruler or have someone assist you.
- Keep your head level and posture natural.
- Take multiple measurements and average them.
IMPORTANCE OF SEGMENT HEIGHT
When SH is accurate, your near vision zones fall exactly where they should. If it’s off, you may experience:
- Blurred near vision
- Neck strain from compensating head movement
- Awkward transitions between viewing zones
- Overall multifocal discomfort
PROGRESSIVE VS. BIFOCAL
Measure to the center of your pupil.
Common range: 18–24 mm
Measure to the lower eyelid.
Common range: 10–14 mm
WHICH SEGMENT HEIGHT TO USE
- Single vision: SH is not required.
- Progressives: Measure pupil center to lens bottom.
- Bifocals: Measure lower eyelid to lens bottom.
- Occupational lenses: May be positioned slightly higher depending on use.
FINDING SH ON YOUR PRESCRIPTION
Your provider may list segment height using one of these abbreviations:
- SH, Seg, or Seg Ht
- Separate OD / OS values (right and left eye)