How To Measure Segment Height

Segment Height, also known as Seg Height or SH, is the vertical measurement in millimeters from the bottom of the lens in your frames, to the beginning of the progressive addition on a progressive lens, or the top line of a lined bifocal. Segment height does not apply to Single Vision lenses. The determined Segment Height is specific to each frame and wearer.

How to Measure Segment Height:
 

Step 1: Set the Stage

Position yourself in a well-lit room with your mirror and materials at the ready.
 

Step 2: Put on Your Glasses

Wear your pair of glasses. This will be your guide to getting the perfect fit.
 

Step 3: Find Your Pupils

Look straight ahead into the mirror and mark the center of each pupil with a small dot or sticky note. These marks are your starting points.
 

Step 4: Measure Down

Using your ruler or measuring tape, measure downward from each pupil mark to the bottom of the lens. This distance is your segment height. Attention: the measurement refers to the bottom of the lens, not the frame.
 

Step 5: Record and Repeat

Note down the segment height for each eye. For accuracy, repeat the process a couple of times to ensure consistency.
 

Step 6: Double-Check for Symmetry

Check that the segment heights for both eyes are symmetrical. If not, make slight adjustments until you achieve balance.

 

* * * DETAILS ON HOW TO MEASURE FOR PROGRESSIVE'S * * *


* * * DETAILS ON HOW TO MEASURE FOR LINED BIFOCAL'S * * *

Most Popular Blog Posts

Phasellus lorem malesuada ligula pulvinar commodo

Frequently asked questions

Have questions? We’re here to help

What is segment height for glasses?

Segment height is the vertical measurement from the lowest point inside the eyeglass frame to the center or top of the reading segment, depending on the lens design. It helps position bifocal, trifocal, and progressive lenses correctly for comfortable vision.

Why is segment height important?

An accurate segment height ensures your reading or progressive viewing area aligns properly with your eyes. An incorrect measurement can make reading uncomfortable, reduce visual clarity, and make it more difficult to adapt to your new glasses.

Which types of lenses require a segment height measurement?

Segment height is typically required for:

  • Progressive (no-line) lenses
  • Flat Top (FT-28) bifocals
  • Trifocal lenses
  • Double segment bifocals
  • Other occupational or specialty multifocal lenses

Single vision lenses generally do not require this measurement.

Can I measure my segment height at home?

Yes. While professional measurements are recommended, you can measure your segment height at home by wearing your chosen frame, looking straight ahead, and marking the appropriate reference point on the lens using a washable marker or removable tape. Measuring while wearing the frame in its natural position provides the most accurate results.

Do I need to wear the frame when measuring segment height?

Yes. Your frame should be adjusted to fit comfortably before measuring. Segment height depends on how the frame sits on your face, so measurements taken without wearing the frame may not be accurate.

Is segment height different for progressive and bifocal lenses?

Yes. Progressive lenses often require the measurement from the bottom of the lens to the center of your pupil. Flat Top bifocals and trifocals typically use different fitting references based on the lens design and your eye care professional's recommendations.

Can I use my old glasses to determine my segment height?

Sometimes. If your current glasses fit well and provide comfortable vision, your previous segment height may serve as a useful reference. However, changing to a different frame size or shape usually requires a new measurement.

Does frame size affect segment height?

Yes. Frame height, frame shape, bridge fit, and how the frame sits on your face all influence the required segment height. A measurement should be taken for the specific frame you plan to order.

What happens if my segment height is incorrect?

An incorrect segment height can place the reading area too high or too low, making it difficult to use your multifocal lenses comfortably. This may lead to blurred vision, neck strain, eye fatigue, or difficulty adapting to your new glasses.

Can VS Eyewear help me measure my segment height?

Yes. The optical experts at VS Eyewear can guide you through measuring your segment height for bifocal, trifocal, progressive, and specialty lenses. We'll help ensure your measurements are as accurate as possible so your custom lenses provide optimal vision and comfort.