Skip to content
ENExplore Calculators

Eye Prescription Conversion Calculator

Work out eye prescription conversion instantly with clear inputs, formula shown and shareable results.

About Eye Prescription Conversion Calculator

Transposes a spectacle prescription between plus and minus cylinder form and reports the spherical equivalent.

Formula

Transposition

New sphere = sphere + cylinder; new cylinder = cylinder with the sign reversed; new axis = axis plus or minus 90 degrees. Spherical equivalent = sphere + cylinder/2

Worked example

With the default values below, Eye Prescription Conversion Calculator returns Transposed sphere of 0.50. Change any input above and every figure here is recalculated in your browser.

Inputs used

Sphereaccepts -30–30 D
2 D
Cylinderaccepts -10–10 D
-1.5 D
Axisaccepts 0–180 degrees
90 degrees

Results

Transposed sphere
0.50 D
Transposed cylinder
1.50 D
Transposed axis
180 degrees
Spherical equivalent
1.25 D

Step by step

  1. 1Values used
  2. 2Transposition
  3. 3Transposed sphere= 0.50 D
  4. 4Transposed cylinder= 1.50 D
  5. 5Transposed axis= 180 degrees
  6. 6Spherical equivalent= 1.25 D

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
  • This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

Why transpose at all?

Optometrists usually write minus cylinder while some laboratories and ophthalmologists use plus cylinder; the lens is identical.

What is the spherical equivalent used for?

It condenses a sphere-cylinder prescription to a single number for screening, contact lens trials and epidemiology.

Related Calculators

Eye Prescription Conversion Calculator | Calcrivo