Type in the numbers from your glasses prescription and get them translated into plain English: whether each eye is nearsighted or farsighted, how much astigmatism you have, what the ADD and PD mean, and which lens index keeps your glasses thin.
Last updated:
Right eye (OD)
D
D
Leave blank or 0 if empty / DS / SPH
°
1 to 180; only used with CYL
D
Left eye (OS)
D
D
°
D
Pupillary distance (optional)
mm
Ignored if you enter two monocular values
mm
mm
Enter your values to see the result.
Advertisement
Advertisement
How to use the Eyeglass Prescription Explained
Find your prescription and locate the OD (right eye) and OS (left eye) rows.
Enter SPH, CYL and AXIS for each eye, keeping the + or − signs. Leave CYL blank if it says DS, SPH or is empty.
Add the ADD value if you have one (bifocals, progressives, readers).
Enter your PD as one number or two monocular numbers.
Read the explanation for each eye and the lens thickness hint.
How to read each part of your prescription
Term
What it means
Typical values
OD / OS / OU
Right eye / left eye / both eyes
—
SPH
Main power in diopters (− nearsighted, + farsighted)
−10.00 to +6.00, in 0.25 steps
CYL
Astigmatism correction power
−0.25 to −4.00 (or plus values in plus-cyl format)
AXIS
Orientation of the cylinder, in degrees
1 to 180
ADD
Extra reading power for multifocals
+0.75 to +3.00
PRISM / BASE
Shifts the image to help eye alignment
Only on some prescriptions
PD
Distance between pupils
54–74 mm (or 27–37 mm per eye)
Severity guide and lens index
Strongest power
Myopia / hyperopia
Suggested lens
up to ±2.00
Mild
1.50 standard or 1.59 polycarbonate
±2.25 to ±4.00
Mild to moderate
1.60 high-index
±4.25 to ±6.00
Moderate (high myopia beyond −6.00)
1.67 high-index
beyond ±6.00
High
1.74 high-index, aspheric
Myopia severity here uses the spherical equivalent: mild to −3.00, moderate −3.25 to −6.00, high beyond −6.00. Hyperopia: mild to +2.00, moderate +2.25 to +5.00, high above +5.00. Lens advice uses the strongest meridian (SPH or SPH + CYL), which decides edge or center thickness.
Plus and minus cylinder notation
The same lens can be written two ways. To convert (transpose): add SPH and CYL to get the new SPH, flip the sign of CYL, and change the axis by 90°. For example, −1.00 +0.75 × 90 is the same as −0.25 −0.75 × 180. Optometrists in the US usually write minus cylinder; some ophthalmologists use plus cylinder.
Frequently asked questions
What do OD and OS mean on a glasses prescription?
OD (oculus dexter) is your right eye and OS (oculus sinister) is your left eye. Some prescriptions use RE and LE instead, and OU means both eyes.
What does SPH mean?
SPH (sphere) is the main lens power in diopters. A minus number means nearsighted: you see near objects better than far ones. A plus number means farsighted. The bigger the number, the stronger the lens.
What do CYL and AXIS mean?
CYL (cylinder) is the extra power that corrects astigmatism, and AXIS (1 to 180 degrees) is the direction in which that power is placed. If CYL is blank or 0, you have no astigmatism correction and the axis is not needed.
How bad is my astigmatism?
As a rough guide, a cylinder up to 1.00 D is mild, 1.25 to 2.00 D moderate, and more than 2.00 D high. Even mild astigmatism can cause eye strain or blurry night vision if it is not corrected.
What is ADD on my prescription?
ADD is extra plus power added to your distance prescription for reading, used in bifocals, progressives or reading glasses. It usually appears after about age 40 because of presbyopia and is often between +0.75 and +3.00.
What is PD and why does it matter?
PD (pupillary distance) is the distance between the centers of your pupils in millimeters, typically 54 to 74 mm in adults. It tells the lab where to put the optical center of each lens. A single number is binocular PD; two numbers are per-eye (monocular) PD.
Can I use my glasses prescription for contact lenses?
No. A contact lens prescription also needs the lens brand, base curve and diameter, and powers above about ±4.00 D change because contacts sit on the eye. You need a separate contact lens fitting.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.