Work out spectacle lens thickness instantly with clear inputs, formula shown and shareable results.
Uses the sagitta approximation to estimate how thick a lens becomes at the edge for a minus prescription, or at the centre for a plus prescription.
Sagitta approximation
Sag (mm) = semi-diameter^2 (mm) x |power| / (2000 x (n - 1)); minus lens edge = centre thickness + sag
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
Going from 1.50 to 1.74 reduces the sag by roughly 40% for the same power and diameter.
Yes. A smaller lens diameter reduces thickness far more effectively than index alone.