What is pupillary distance (PD) and how do I calculate it?

PD is the distance in millimetres between the centres of your pupils while you look into the distance. A single PD such as 63 is the total; a dual PD such as 31.5/31.5 gives each eye's distance from the middle of the nose bridge (right eye first), and the two add up to the total. Most adults measure 54–74 mm; in the US Army ANSUR survey the average was 62.3 mm for women and 64.7 mm for men.

How do I measure my PD at home with a ruler?

Stand about 8 inches (20 cm) from a mirror and hold a millimetre ruler flat against your brow. Close your right eye and line up the 0 mark with the centre of your left pupil. Without moving the ruler, close your left eye, open your right eye and read the mark at the centre of your right pupil — that number is your distance PD. Repeat three times and average. A friend measuring you while you look past them at a distant object is more accurate than a mirror.

How do I calculate near PD from distance PD?

Near PD = distance PD × L ÷ (L + 27), where L is the reading distance in millimetres and 27 mm is the conventional distance from the lens to the eye's centre of rotation. At 40 cm the factor is 0.937, so 64 mm becomes 60 mm, 62 becomes 58.1 mm and 68 becomes 63.7 mm. Holding things closer increases the difference: 64 mm at 25 cm gives 57.8 mm. The quick shortcut "subtract 3 mm" gives 61 for a 64 PD; the geometry gives a 4 mm difference at 40 cm.

Distance PD is 68 mm and near PD is 64 mm. What are the total convergence, convergence per eye and intermediate PD?

Total convergence = 68 − 64 = 4 mm, which is 2 mm per eye (each eye turns in 2 mm, which is also the segment inset for a bifocal). An intermediate PD is usually taken halfway between distance and near, so 66 mm (33/33). By the 27 mm geometry, a 68 mm PD would converge to 63.7 mm at 40 cm and 65.1 mm at 60 cm, so a measured near PD of 64 corresponds to a slightly closer reading distance.

What PD should I use for computer glasses (intermediate PD)?

Use your PD at the screen distance. With the calculator's geometry, a 64 mm distance PD is 61.2 mm at 60 cm and a 62 mm PD is 59.3 mm. A common shortcut is distance PD minus about 1–2 mm — between the distance value and the reading value. Set the computer distance field to how far you actually sit from the monitor.

What does a PD written as 62/58 or "dist 60 near 57" mean?

Two numbers separated by a slash with a large gap are usually distance PD / near PD: 62/58 means 62 mm for distance glasses and 58 mm for reading glasses (the geometric near PD for 62 at 40 cm is 58.1 mm). "Dist 60 near 57" is the same idea; 60 mm at 40 cm gives 56.2 mm, so a measured 57 suggests a reading distance of about 51 cm. If the two numbers are close (such as 31/32), it is a dual (monocular) PD instead.

I have two PD numbers. Which one goes on an order for progressive or distance glasses?

Use the distance (far) PD for single-vision distance glasses, sunglasses and progressives — the lab calculates the near inset for progressives from the distance PD. Use the near PD only for glasses you will use just for reading. If you have a dual PD such as 32/31, enter both numbers where the form allows it; otherwise add them (63) for a single PD.

What do 31.5/31, "28 OD and 28 OS" and "35 35" mean?

These are dual (monocular) PDs. OD is the right eye and OS the left; the right eye is written first. 31.5/31 means 31.5 mm for the right eye and 31 mm for the left, a 62.5 mm total. 28 OD / 28 OS adds up to a 56 mm PD, and 35/35 is a 70 mm PD. A 0.5 mm difference between eyes is common and still matters for progressives, so keep both numbers rather than splitting the total in half.

How do I convert a PD from centimetres or inches to millimetres?

Multiply centimetres by 10 and inches by 25.4. 3 cm = 30 mm; 6 cm = 60 mm; 6.3 cm = 63 mm; 2 1/2 in = 63.5 mm; 2 1/4 in = 57.1 mm; 2 7/8 in = 73 mm. A total PD of 3 cm (30 mm) is impossible for an adult — that is a one-eye PD, so the total is about 60 mm. 62 mm is 2.44 in (≈ 2 7/16 in). A reading of 6 inches or 10.5 cm (152 or 105 mm) is not a PD — you have measured something else, such as face width.

What is the average pupillary distance?

In the 1988 ANSUR anthropometric survey of 3,976 US Army personnel, the mean PD was 63.36 mm (SD 3.83), ranging from 52 to 78 mm. Women averaged 62.31 mm and men 64.67 mm. About 90% of adults fall between 57.1 and 69.7 mm.

What is the average PD by ethnicity — for example, for a Black man around 5 ft 8 in?

ANSUR reports PD by race (men and women combined): White 62 mm, Black 65.6 mm, Hispanic 63.5 mm, Asian / Pacific Islander 63.2 mm, American Indian 65.1 mm. Men measure about 2.4 mm more than women on average, so a Black man would typically be a little above 65.6 mm. Height is not a dependable predictor — the survey reports PD by sex and race, not by stature — so measure rather than estimate.

Can a PD be 66 mm or 70 mm? Is that normal?

Yes. 66 mm is about the 64th percentile for men, the 85th for women and the 75th overall — very common. 70 mm is wider than about 96% of adults but well inside the 52–78 mm range in the survey. Values under 50 mm are normal for children; for adults they usually mean a measuring or unit mistake.

How accurate does my PD need to be? What is the PD tolerance?

ANSI Z80.1 (the US lab standard) limits horizontal prism imbalance to 0.67 prism dioptres. For single-vision lenses up to ±2.75 D that tolerance is checked as prism; above ±2.75 D the optical centres must be within ±2.5 mm of the ordered PD. Progressives are stricter: for powers above ±3.375 D each fitting cross must be within ±1 mm of the monocular PD. In practice, a 1–2 mm error rarely matters for mild prescriptions but can cause eye strain with strong or progressive lenses.

Is 64 versus 65 mm a big difference for progressive lenses?

A 1 mm total difference is 0.5 mm per eye. With a −2.00 D lens that creates only 0.2 prism dioptres in total, well under the 0.67Δ limit, so for typical powers it is within tolerance. Progressives are more sensitive in practice because a narrow reading corridor that is off-centre feels like a reduced field of view, so use your most reliable dual PD rather than rounding.

How do I calculate decentration? PD 67 with a 55/19 frame.

Frame PD = lens width + bridge = 55 + 19 = 74 mm. Decentration per eye = (frame PD − PD) ÷ 2 = (74 − 67) ÷ 2 = 3.5 mm. The frame PD is wider than the patient's PD, so each optical centre moves 3.5 mm in (toward the nose). With dual PD, use frame PD ÷ 2 − monocular PD for each eye.

PD 64 and a 52□20 frame: how much decentration, and in which direction?

Frame PD = 52 + 20 = 72 mm, so decentration = (72 − 64) ÷ 2 = 4 mm per eye, inward (nasal), because the patient's PD is smaller than the frame PD. With an effective diameter of 56 mm the minimum blank size is 56 + 2 × 4 + 2 = 66 mm.

How is near PD checked on a lined bifocal?

Measure the distance between the centres of the two bifocal segments at final inspection. ANSI Z80.1 allows the segment centres to be within ±2.5 mm of the specified near PD in total. Each segment should be inset from the distance optical centre by about half the convergence — for a 64 mm PD at 40 cm that is 2 mm per eye (near PD 60 mm).

What happens if the PD on my glasses is wrong?

The optical centres no longer line up with your pupils, so the lenses act like weak prisms (Prentice's rule: prism = decentration in cm × lens power). Glasses made at 66 mm for a 62 mm PD with −4.00 D lenses give 0.8Δ base in per eye, 1.6Δ in total, and the 4 mm PD error is outside the ±2.5 mm ANSI tolerance for that power. With +2.00 D lenses made 2 mm too narrow, the total is 0.4Δ base in, which is acceptable. Common symptoms are eye strain, headaches and a "pulling" sensation, and they stop when the lenses are remade.

Can I measure my PD online with a photo or credit card?

Yes. Online tools from eyewear retailers and apps use a standard card (85.6 mm wide, ISO/IEC 7810 ID-1) or the phone's depth camera as a scale. You can do the same by hand: photograph yourself with a card on your forehead, measure the card width and the pupil distance in pixels, and use the "PD from photo" tab — PD = pupil pixels ÷ card pixels × 85.6. Expect accuracy of about 1–2 mm; average several photos.

What is a normal PD for a child?

Children have smaller PDs that grow with the face. Dodgson's review of the anthropometric data puts the lower limit for children aged 5 and over at about 40 mm, compared with roughly 50–75 mm for most adults. PD keeps increasing until about age 19 in boys and 14 in girls, so re-measure for every new pair of glasses. Children's frames have narrower bridges to match.

Near PD is 58 mm at a 20-inch working distance. What is the distance PD?

Reverse the formula: distance PD = near PD × (L + 27) ÷ L. 20 inches is 508 mm, so 58 × 535 ÷ 508 = 61.1 mm. The calculator's Near & computer PD tab will confirm it: enter 61.1 mm and a reading distance of 51 cm.

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Pupillary distance · near PD · decentration

PD Calculator (Pupillary Distance Calculator)

Quick answer

Your PD is the distance between your pupil centres in millimetres — most adults measure 54–74 mm, averaging 62.3 mm for women and 64.7 mm for men. To get near PD, multiply distance PD by L ÷ (L + 27), with L the reading distance in mm: at 40 cm, 64 mm → 60 mm (about 3–4 mm less), and 61.2 mm for a computer at 60 cm. A dual PD like 32/32 is each eye's share; add them for a single PD. Use distance PD for most glasses, including progressives.

Enter your PD in mm, cm or inches (fractions like 2 1/2 work) to get near and computer PD, convergence and seg inset, and how you compare with the population. The other tabs work out frame PD and decentration from the numbers on your frame, the prism caused by glasses made at the wrong PD, and your PD from a photo with a card.

Near & intermediate PD by real optics, not a fixed −3 mm
Single or dual PD; mm, cm, decimal or fractional inches
Frame PD, decentration direction and minimum blank size
Prentice's-rule prism check against ANSI Z80.1

Last updated October 1, 2026. Formulas from Jalie's Fitting of Spectacle Lenses, ANSI Z80.1-2015 and ANSUR anthropometric data. Educational — not a substitute for a measured PD from an optician. · near PD · average PD

PD Calculator

Near and computer PD, frame decentration, prism from a wrong PD, and PD from a photo.

Distance PD (mm)

The number on your prescription, or your ruler reading. Fractions like 2 7/16 work.

Reading distance (cm)

40 cm (16 in) is the standard near distance; use 33 cm for close work

Computer distance (cm)

Typical monitor distance is 50–70 cm (20–28 in)

Distance PD

63 mm

31.5 / 31.5 per eye · 2.48 in (≈ 2 1/2 in)

Near PD (40 cm)

59 mm

29.5 / 29.5 per eye · reading glasses

Computer PD (60 cm)

60.3 mm

30.1 / 30.1 per eye

Convergence & seg inset

Eyes turn in 4 mm in total at 40 cm — an inset of 2 mm (right) and 2 mm (left) for bifocal segments or progressive near zones. Quick rule (distance − 3): 60 mm.

How your PD compares

63 mm is about the 58th percentile for women, 33rd for men and 46th for all adults (US Army ANSUR survey, mean 62.3 mm women, 64.7 mm men).

What to type on an order form	Value (mm)
Single (binocular) distance PD	63
Dual (monocular) distance PD, right/left	31.5/31.5
Near PD for reading glasses (40 cm)	59
Computer PD (60 cm)	60.3
Two-number format (distance/near)	63/59

How it was calculated

Distance PD = 63 mm → 31.5 mm per eye if your face is symmetric
Near PD = distance PD × L ÷ (L + 27 mm), L = 400 mm → 63 × 0.937 = 59 mm
Convergence = 63 − 59 = 4 mm total (seg inset 2 mm right, 2 mm left)
Computer PD at 60 cm = 63 × 0.957 = 60.3 mm
Rule of thumb for comparison: 63 − 3 = 60 mm

How near PD is calculated from distance PD

Your eyes rotate about a point about 27 mm behind the spectacle lens. When you look at something at distance L, each visual axis crosses the lens closer to the nose. By similar triangles, near PD = distance PD × L ÷ (L + 27 mm), applied to each eye for dual PD. The difference between distance and near PD is the total convergence, and half of it (per eye) is the inset for bifocal segments and progressive reading zones.

Reading (40 cm)

64 × 400 ÷ 427 = 60 mm; inset 2 mm per eye

Computer (60 cm)

64 × 600 ÷ 627 = 61.2 mm

Close work (25 cm)

64 × 250 ÷ 277 = 57.8 mm; the "−3 mm" rule underestimates this

Near PD chart: distance PD vs working distance

Total near PD in mm for each reading or screen distance (s = 27 mm). 40 cm (16 in) is the standard reading distance.

Distance PD	33 cm (13 in)	40 cm (16 in)	50 cm (20 in)	60 cm (24 in)	70 cm (28 in)	Quick rule (−3)
54 mm	49.9	50.6	51.2	51.7	52	51
56 mm	51.8	52.5	53.1	53.6	53.9	53
58 mm	53.6	54.3	55	55.5	55.8	55
60 mm	55.5	56.2	56.9	57.4	57.8	57
62 mm	57.3	58.1	58.8	59.3	59.7	59
63 mm	58.2	59	59.8	60.3	60.7	60
64 mm	59.2	60	60.7	61.2	61.6	61
66 mm	61	61.8	62.6	63.2	63.5	63
68 mm	62.9	63.7	64.5	65.1	65.5	65
70 mm	64.7	65.6	66.4	67	67.4	67
72 mm	66.6	67.4	68.3	68.9	69.3	69

Pupillary distance chart: average PD for adults

Percentiles from the US Army ANSUR survey (n = 3,976, ages 17–51), assuming a normal distribution. 90% of people fall between the 5th and 95th percentile.

Group	5th	25th	50th	75th	95th	Range
Women	56.4	59.9	62.3	64.7	68.2	52–76
Men	58.6	62.2	64.7	67.2	70.8	52–78
All adults	57.1	60.8	63.4	65.9	69.7	52–78

Group (men + women)	n	Mean PD	SD
White	2,302	61.99	3.43
Black	1,376	65.62	3.49
Hispanic	125	63.54	3.1
Asian / Pacific Islander	58	63.17	3.15
American Indian	26	65.12	4

How to measure your PD at home

Ruler and mirror — the method used by the VA and Cleveland Clinic

Get a millimetre ruler. Use a ruler marked in mm, or print a PD ruler at 100% scale and check it against a real ruler.
Line up the left pupil. Stand about 8 inches (20 cm) from a mirror, hold the ruler on your brow, close your right eye and set 0 at the centre of your left pupil.
Read the right pupil. Close your left eye and open your right eye. The mark at the centre of the right pupil is your distance PD in mm.
Repeat and average. Measure three times and average. For dual PD, measure from the centre of the nose bridge to each pupil.
Calculate near and computer PD. Multiply by L ÷ (L + 27 mm) for your working distance — 0.937 at 40 cm for reading — or enter your PD in the calculator.

Printable PD rulers only work at 100% scale — check the 10 cm mark against a real ruler before using one. A friend measuring you is more reliable than a mirror.

Single vs dual PD: what to order

Which number goes in which box

Single PD (one number, e.g. 63): the total. Fine for most single-vision glasses.
Dual PD (e.g. 32/31): right eye (OD) first, left eye (OS) second. Preferred for progressives and strong prescriptions because few faces are perfectly symmetric.
Two numbers far apart (e.g. 63/60): distance/near. Use the first for distance glasses and progressives, the second for reading-only glasses.
Computer glasses: use the intermediate PD for your screen distance — for 64 mm at 60 cm, 61.2 mm.

PD in mm, cm and inches

PD is always ordered in millimetres. 1 cm = 10 mm; 1 inch = 25.4 mm.

PD (mm)	cm	Inches	Per eye (mm)	Near PD at 40 cm
50	5	1.97 in (≈ 1 15/16 in)	25	46.8
54	5.4	2.13 in (≈ 2 1/8 in)	27	50.6
56	5.6	2.20 in (≈ 2 3/16 in)	28	52.5
58	5.8	2.28 in (≈ 2 5/16 in)	29	54.3
60	6	2.36 in (≈ 2 3/8 in)	30	56.2
62	6.2	2.44 in (≈ 2 7/16 in)	31	58.1
63	6.3	2.48 in (≈ 2 1/2 in)	31.5	59
64	6.4	2.52 in (≈ 2 1/2 in)	32	60
66	6.6	2.60 in (≈ 2 5/8 in)	33	61.8
68	6.8	2.68 in (≈ 2 11/16 in)	34	63.7
70	7	2.76 in (≈ 2 3/4 in)	35	65.6
73	7.3	2.87 in (≈ 2 7/8 in)	36.5	68.4

Frame PD and decentration

The numbers on a frame temple such as 52□18 140 are the lens width (A), bridge (DBL) and temple length. Frame PD = A + DBL is the distance between the centres of the two lens openings. The lab moves each optical centre by (frame PD − PD) ÷ 2 to put it in front of your pupil — inward when the frame PD is wider than your PD, which is almost always the case.

PD 67 · 55□19

Frame PD 74 mm

R 3.5 mm in, L 3.5 mm in

PD 64 · 52□20 · ED 56

Frame PD 72 mm

R 4 mm in, L 4 mm in

Min blank 66 mm

PD 31/33 · 50□18

Frame PD 68 mm

R 3 mm in, L 1 mm in

PD 70 · 48□18

Frame PD 66 mm

R 2 mm out, L 2 mm out

Decentration per eye (mm, inward) for a 62 mm PD:

Lens width (A)	Bridge 16	Bridge 18	Bridge 20	Bridge 22
48 mm	1	2	3	4
50 mm	2	3	4	5
52 mm	3	4	5	6
54 mm	4	5	6	7
56 mm	5	6	7	8
58 mm	6	7	8	9

Smaller decentration means a smaller lens blank and thinner edges for strong prescriptions. Values over 5 mm are highlighted — a narrower frame would fit better.

How much PD error is acceptable? (ANSI Z80.1)

A wrong PD moves the optical centres away from your pupils, creating prism by Prentice's rule: prism (Δ) = decentration (cm) × power (D). A plus lens centred too wide gives base-out prism; a minus lens centred too wide gives base-in. US labs use these tolerances:

Lens	Power	Tolerance
Single vision & multifocal	0 to ±2.75 D	Horizontal prism imbalance ≤ 0.67Δ total
Single vision & multifocal	Above ±2.75 D	Optical centres within ±2.5 mm of the ordered distance PD
Progressive	0 to ±3.375 D	Horizontal prism imbalance ≤ 0.67Δ total
Progressive	Above ±3.375 D	Each fitting cross within ±1.0 mm of the monocular PD
Multifocal segments	Any	Segment centres within ±2.5 mm of the specified near PD

−4.00 D, made at 66 for a 62 PD

0.8Δ per eye → 1.6Δ base in total

Outside ANSI tolerance — remake

+2.00 D, made at 62 for a 64 PD

0.2Δ per eye → 0.4Δ base in total

Within ANSI tolerance

−2.00 D, made at 65 for a 64 PD

0.1Δ per eye → 0.2Δ base in total

Within ANSI tolerance

When to get your PD measured professionally

Ask an optician for a pupillometer reading for progressives, prescriptions stronger than about ±4.00 D, prescribed prism, or children. Opticians also measure fitting height, which you cannot calculate at home. If new glasses cause headaches or double vision, have the optical centres checked before changing the prescription.