Segment Height for Progressive Lenses Explained

Segment height is the vertical distance from the centre of your pupil down to the lowest edge of the lens opening in your frame. For progressive lenses it decides how much room the lens has for its distance, intermediate and reading zones, so a frame that is too shallow can squeeze the reading area. In practice, choose a frame with a generous lens height and keep the fitting measurement with your prescription details.

What segment height actually measures

A progressive lens is not one power but a gradual change in power from top to bottom. The top area is set up for distance, a narrow channel in the middle (often called the corridor) handles mid-range tasks, and the lower part carries your reading addition.

Segment height tells the lab where your eye sits inside the frame. With that number, the lens can be positioned so that you look straight through the distance zone when your head is level, and drop your gaze naturally into the reading zone when you look down at a book or phone.

• Measured from: the centre of the pupil, with you looking straight ahead.
• Measured to: the deepest point of the lens opening inside the rim, directly below the pupil.
• Measured per eye: left and right can differ slightly, because faces are rarely perfectly symmetrical.

It sits next to pupillary distance (PD) on a full fitting record. PD sets the horizontal position; segment height sets the vertical one. Our guide on measuring pupillary distance covers the horizontal half of the picture.

Why the frame matters as much as the number

Segment height belongs to a specific frame on a specific face. Move to a deeper or shallower frame, or a frame that sits higher on your nose, and the number changes. That is why it is taken with the chosen frame on, not copied from an old pair.

The bigger issue is space. If the pupil sits only a short distance above the bottom rim, the lens has little vertical room left after the distance zone, and the reading area can end up small or partly cut off by the frame. Many wearers describe this as having to tilt their head back to find the reading spot.

A frame with a taller lens opening gives the progression more room to unfold. That is the single most useful thing to look for when you shop.

Lens height: the number to check before you buy

Every frame on our site lists its measurements, including lens height (the full vertical size of the lens opening). It is a good first filter, because a deeper lens leaves more room below the pupil. The frame size guide explains where each figure comes from.

Frame	Shape	Lens height	Lens width
AvonPaK-FC29	Round, double bridge	46 mm	47 mm
Kenosha-FL38	Square	41 mm	52 mm
Amory-FC04	Rectangle	41 mm	54 mm
Arnect-FC14	Square	36 mm	50 mm

Lens height is not the same as segment height. A 41 mm lens does not give you 41 mm under the pupil; your eye usually sits somewhere above the middle of the lens. Still, a deep frame starts you off with far more margin than a slim one.

Frame styles that help, and ones to treat with care

Some shapes naturally suit progressive wearers better than others:

• Square and rectangle frames with real depth keep plenty of lens below the eye across the whole width. See the square frames for options.
• Round and panto shapes often have a generous vertical size in the centre, right where the reading zone lands.
• Thin, wide "letterbox" rectangles look sleek but can leave little room under the pupil. Check the lens height first.
• Strongly tapered cat-eye or aviator bottoms can cut into the lower inner corner, which is where your eyes converge for reading.

Fit on the nose matters too. A frame that slides down changes your effective segment height every time it moves, so a secure bridge and temples are part of good progressive performance.

How segment height is usually taken

The most reliable measurement comes from an optician with the frame adjusted on your face. They mark the pupil centre on the demo lens or use a digital measuring device while you look straight ahead in a relaxed posture.

If you are curious about checking it yourself, the basic idea looks like this:

1. Put the frame on and adjust it so it sits where you would normally wear it.
2. Stand in front of a mirror at eye level, head straight, looking at your own eyes.
3. Have a helper note the point on the lens directly over each pupil centre.
4. Measure straight down from that point to the inside bottom of the rim, in millimetres.

Home results are approximate, and small errors move the reading zone noticeably. Treat a DIY number as a sense check, not a replacement for a professional fitting record. If your prescription paperwork already lists a fitting or segment height, keep it together with your prescription values.

Signs the height is off

When segment height is set too low or too high, the lens itself can be perfect and still feel wrong. Common signs include:

• Needing to lift your chin to see distant objects clearly (zones set too high).
• Having to push your glasses up or tip your head back to read (zones set too low).
• One eye finding the reading area sooner than the other.

Some adjustment period is normal with any new progressive pair; our article on adapting to first-time progressives explains what to expect. Persistent head-tilting after that period is worth raising with an optician.

Frequently asked questions

Is segment height the same as fitting height?

For progressive lenses the terms are generally used for the same measurement: pupil centre to the bottom of the lens opening. With bifocals, segment height refers to the top of the visible reading segment instead.

Can I reuse the segment height from my old glasses?

Only if the new frame is the same model, worn the same way. A different frame depth or bridge position changes the measurement.

What lens height should I look for in progressive frames?

Deeper is generally easier. Many wearers find frames with a lens height in the high 30s or 40s mm comfortable, while very slim frames call for a closer look at where your eye will sit.

Do single vision lenses need a segment height?

Not in the same way. Single vision lenses have one power across the lens, so there are no zones to position vertically.

Shop this guide

Amory-FC04Shop nowArnect-FC14Shop nowAvonPaK-FC29Shop nowKenosha-FL38Shop now

Choose a frame with room to read

Good progressive vision starts with a frame that leaves space below the eye. Browse our progressive eyeglasses, compare lens heights on each product page, or explore the wider acetate frames and all eyeglasses ranges. Add your prescription in a few clicks with our lens selector.