Progressive Lens Fitting Calculator

A higher add power means a bigger jump between distance and near prescription packed into the same lens, and shortening the corridor is one way lens designers compress that transition into less vertical space. It's a genuine tradeoff: a shorter corridor allows a smaller frame, but concentrates the power change into less area, which is why higher-add wearers sometimes notice more peripheral distortion in the intermediate zone with short-corridor designs.

The reading zone at the bottom of the lens can end up too narrow or effectively cut off, since there isn't enough vertical room below the corridor to fit a usable near zone. This is one of the most common reasons patients reject a new pair of progressive lenses after the fact, which is why checking frame height against your add power before ordering lenses -- not after -- is standard practice for smaller or fashion-forward frames.

No -- this calculator checks pupil height (which sets the fitting point) together with frame height against the minimum height your add power requires. A tall enough frame with a pupil height that's too low relative to the lens opening can still fail the fit, since the fitting height itself needs to be at least as large as the recommended corridor length for the reading zone to have room below it.

This calculator adds roughly 4mm above the fitting point for the distance zone and roughly 4mm below the corridor for a minimum usable reading zone, on top of the corridor length itself. That's a working estimate, not a universal standard -- exact minimums vary somewhat by lens manufacturer and design, so your optician's own fitting guide for the specific lens you choose is the more precise reference.