Optical Tools and Free Optical Calculators

Fifteen calculators for the sums that come up at the dispensing counter and in the lab, grouped by the job you are doing. Each one opens on its own page with the formula, worked examples and its limits. They are free and need no account.

Prescription

For rewriting or reducing a prescription that has already been measured.

Lens and frame

For choosing a blank, checking a frame and predicting how a finished lens will behave.

Low vision

Reference calculations for low vision aids. They are estimates, not an assessment.

Guides

Background reading for the numbers these calculators take.

Before you use a result

  • Enter values as they are written on the prescription, with their signs. Powers are in dioptres, lengths in millimetres and axes from 1 to 180 unless a page says otherwise.
  • Results are rounded for display. Lenses are ordered in 0.25 D steps, so round to the step your supplier works in.
  • The calculators run in your browser and do arithmetic on the numbers you type. They do not examine an eye or replace a qualified practitioner; check a result before it is used to order or dispense a lens. Medical and calculation disclaimer.

The same calculations, inside the shop software

Asaan Optics is optical shop software for Windows and Android. It keeps prescriptions, billing, stock and repair jobs together, and both apps include a set of optical calculators.

Desktop software Mobile app
Free optical calculators in Asaan Optics: transposition calculator converting -2.00 +1.00 × 90 from plus to minus cylinder (-1.00 -1.00 × 180, spherical equivalent -1.50 D), beside the spherical equivalent, crossed cylinders, Prentice's rule, resultant prism, decentration, minimum blank size, lens thickness and base curve calculators
Vision Calculators in Asaan Optics desktop, with demo data.

Watch: the calculators inside the Asaan Optics desktop app

This video is a tour of the calculators built into the desktop app, not of the web calculators listed on this page. The two lists overlap, but they are not the same.

Video, 1 min 41 s

This is a tour of the optical calculators for opticians built into Asaan Optics: nineteen of them, in five groups, from transposition to pricing and margin. You see how to find one with the search box, type your own values and read the result as it updates, using a spherical equivalent example (sphere -3.00, cylinder -1.00, giving -3.50 D).

Chapters

  1. 00:00Open Vision Calculators
  2. 00:26Search and enter values
  3. 00:51Read, copy and reset

What the video covers

  • Where Vision Calculators is in the menu, and the five groups: Prescription, Lens and Frame, Contact Lens, Vision and Age, Shop and Business
  • How the search box narrows the list as you type
  • Why the minus sign must be typed: a number without a sign is read as plus
  • A spherical equivalent example: -3.00 with -1.00 cylinder gives -3.50 D, the sphere plus half the cylinder
  • What How it works, Copy result and Reset do in every calculator
Transcript

Find and use any of the optical calculators in Asaan Optics. Asaan Optics has nineteen optical calculators built in.

In the menu, open Vision Calculators. They are listed on the left, in five groups. Prescription, and Lens and Frame. Then Contact Lens, Vision and Age, and Shop and Business.

Type a word in the search box. The list narrows as you type. Click Spherical Equivalent to open it.

Each calculator opens with example values. Type your own: sphere minus three, cylinder minus one. Type the minus sign for a minus power. Without a sign, the number is read as plus.

The result changes as you type. The spherical equivalent is minus three point five zero dioptres: the sphere, plus half the cylinder. How it works shows the formula. Copy result puts the answer on the clipboard. Reset brings back the example values. Four more videos cover them in detail: prescription maths, lens ordering, prism and near vision, and contact lenses and more. These tools support your professional judgement. They do not replace it. Search, open, type your values, and read the result.

All video tutorials