McNamara analysis explained: the nasion perpendicular, jaw lengths and airway

Simplified Orthodontics Academy · Published 29 October 2026

Key points

The McNamara analysis relates the maxilla and the mandible to the cranial base and to each other [1]. Simplified Ceph also shows the incisors and two airway distances.
Its main reference line is the nasion perpendicular: a line through nasion at a right angle to Frankfort horizontal (FH).
Most readings are distances in millimetres, measured parallel to FH from the nasion perpendicular or from a vertical through point A.
Effective midfacial length (Co-A) is a size reference. Simplified Ceph takes the expected mandibular length and lower face height for that Co-A from a table of standards.
Simplified Ceph shows the published reference value next to each reading. This article explains what each reading measures and gives no reference values.

What the McNamara analysis is

McNamara described his method of cephalometric evaluation in 1984. It relates the maxilla and the mandible to the cranial structures and to each other [1]. Many of its readings are linear distances rather than angles, so they are read in millimetres on a calibrated radiograph.

Like every cephalometric analysis, it is measured from landmarks: points placed on the radiograph at defined sites [2]. The definitions in this article are the ones Simplified Ceph uses, so the description matches what the tool measures. Other books and programs may define a point or a line slightly differently.

Simplified Ceph groups the McNamara readings in five parts: the maxilla to the cranial base, the maxilla to the mandible, the mandible to the cranial base, the dentition, and the airway. Fourteen readings in all.

The reference lines

Frankfort horizontal (FH): from porion (Po), the highest point on the upper margin of the external auditory meatus, to orbitale (Or), the lowest point on the lower margin of the orbit. Simplified Ceph uses anatomic porion, not the ear rod.
Nasion perpendicular: a line through nasion (N) at a right angle to FH.
Point A vertical: a line through point A, parallel to the nasion perpendicular.
A-Pog line: from point A to pogonion (Pog), the most anterior point of the bony chin.
Effective lengths: straight lines from condylion (Co), the most posterosuperior point on the head of the condyle, to point A and to gnathion (Gn).

A distance “to the nasion perpendicular” is measured parallel to FH. In Simplified Ceph it is positive when the point lies in front of the line and negative when it lies behind it.

Figure 1. The nasion perpendicular on the Simplified Ceph sample tracing. Point A lies on it in this tracing, so here the point A vertical is the same line. The short lines show pogonion to the nasion perpendicular and the upper incisor to the point A vertical. On the profile: the nasolabial angle (NLA) and the cant of the upper lip. Drawn from the sample’s landmark coordinates; a drawn example, not a patient.

The measurements in Simplified Ceph

Maxilla to cranial base

Nasolabial angle: the angle at subnasale (Sn) between the line to the columella point (Cm), the most anterior point on the columella, and the line to labrale superius (Ls), the most anterior point of the upper lip.
Cant of the upper lip: the angle between the line Sn-Ls and a line through Sn at a right angle to FH, that is, parallel to the nasion perpendicular. It is positive when Ls lies in front of Sn.
Point A to nasion perpendicular: the distance from the nasion perpendicular to point A, parallel to FH.

The reference value shown for the lip cant depends on the sex entered in the case details, and the one for point A on the dentition entered there (mixed or permanent).

Maxilla to mandible

Effective midfacial length (Co-A): the distance from condylion to point A. Simplified Ceph uses it as the size reference for the table of standards, and shows no reference value for it.
Effective mandibular length (Co-Gn): the distance from condylion to gnathion, the most anterior-inferior point on the outline of the chin.
Maxillomandibular differential: Co-Gn minus Co-A.
Lower anterior facial height: the distance from the anterior nasal spine (ANS) to menton (Me), the lowest point on the outline of the symphysis.
Mandibular plane angle: the angle between FH and the line from gonion (Go) to menton.
Facial axis angle: the angle between the line from basion (Ba) to nasion and the line from point Pt to gnathion, minus 90°. It is 0° when the two lines cross at a right angle. Pt is the junction of the lower border of the foramen rotundum with the back wall of the pterygomaxillary fissure.

For mandibular length and lower face height, Simplified Ceph does not use one fixed value. It looks up the expected values for the patient’s own Co-A in a table of standards and shows that row under the analysis. If Co-A lies outside the table, the tool shows no expected value and asks you to check the calibration and magnification. The reference value for the differential also depends on Co-A.

Mandible to cranial base

Pogonion to nasion perpendicular: the distance from the nasion perpendicular to pogonion, parallel to FH. Simplified Ceph picks its reference value by the size of Co-A, or, when Co-A is not available, by sex and dentition.

Dentition

Upper incisor to point A vertical: the distance from the point A vertical to the most labial point of the upper incisor crown (U1f), parallel to FH. If U1f is not placed, Simplified Ceph uses the incisal edge.
Lower incisor to A-Pog: the distance from the incisal edge of the lower incisor to the A-Pog line, at a right angle to the line. It is positive when the incisor lies in front of the line.

Airway

Upper pharynx: the distance from UP1, the point on the back outline of the front half of the soft palate that lies closest to the pharyngeal wall, to UP2, the closest point on the posterior pharyngeal wall.
Lower pharynx: the distance from LP1, where the back border of the tongue crosses the lower border of the mandible, to LP2, the closest point on the posterior pharyngeal wall.

Both airway readings are single distances on a two-dimensional image, taken at one moment, with the head and tongue in whatever position they had when the film was taken.

Figure 2. The effective midfacial length (Co-A), the effective mandibular length (Co-Gn), the lower anterior facial height (ANS-Me) and the two airway distances, on the sample tracing without its soft tissue outline.

Worked example: the sample tracing

Simplified Ceph has a built-in sample tracing (Load a sample tracing). It is a drawn example, not a patient. We computed the McNamara readings on it with the tool’s own code, as the tool shows them when the sample is loaded: calibrated, profile facing right, entered as a 25-year-old female with permanent dentition. Age, sex and dentition change only which reference values are shown, not the readings.

Reading	Points	Sample tracing
Nasolabial angle	Cm, Sn, Ls	101.2°
Cant of the upper lip	FH, Sn, Ls	8.1°
Point A to nasion perpendicular	FH, N, A	0.0 mm
Effective midfacial length (Co-A)	Co, A	91.2 mm
Effective mandibular length (Co-Gn)	Co, Gn	118.1 mm
Maxillomandibular differential	Co, A, Gn	26.9 mm
Lower anterior facial height (ANS-Me)	ANS, Me	65.5 mm
Mandibular plane angle (Go-Me to FH)	FH, Go, Me	24.5°
Facial axis angle	Ba, N, Pt, Gn	3.3°
Pogonion to nasion perpendicular	FH, N, Pog	−3.0 mm
Upper incisor to point A vertical	FH, A, U1f	4.3 mm
Lower incisor to A-Pog	A, Pog, L1	2.1 mm
Upper pharynx	UP1, UP2	17.7 mm
Lower pharynx	LP1, LP2	12.0 mm

Point A lies exactly on the nasion perpendicular in this drawing (0.0 mm), so the point A vertical is the same line (Figure 1). Pogonion lies 3.0 mm behind it.
The differential is the difference of the two lengths above it: 118.1 − 91.2 = 26.9 mm.
The facial axis angle, 3.3°, is the Ricketts facial axis of this tracing (93.3°) minus 90°. The Ricketts analysis article uses the same two lines.
The mandibular plane angle, 24.5°, is the same Go-Me to FH angle that the Downs and Ricketts analyses report for this tracing.

Two changes show what the readings depend on. We moved one point at a time and left every other point where it was.

Change	Point A to N perp.	Pog to N perp.	Co-A	Co-Gn	Differential
None (sample tracing)	0.0 mm	−3.0 mm	91.2 mm	118.1 mm	26.9 mm
Orbitale 1 mm higher	−0.7 mm	−4.4 mm	91.2 mm	118.1 mm	26.9 mm
Condylion 2 mm further back	0.0 mm	−3.0 mm	93.1 mm	119.5 mm	26.4 mm

Raising orbitale by 1 mm tilts FH, and with it the nasion perpendicular. Point A moved 0.7 mm and pogonion 1.4 mm relative to the line, although neither moved. Pogonion lies further below nasion than point A, so the same tilt moves it more.
Moving condylion changes both lengths, but not by the same amount, so the differential changes too. Co-A also changes, so Simplified Ceph reads a different row of the table of standards.

Limits

Landmarks are placed by eye. Condylion, point A, pogonion and the airway points sit on curved or faint outlines. Two careful people can place a point on a curve in different spots [3]. The cephalometric landmarks article covers identification error.
Everything hangs on FH. The nasion perpendicular and the point A vertical are built at a right angle to FH, so an error in porion or orbitale changes every distance measured from them, as the worked example shows.
Millimetres need calibration. Distances are only as accurate as the calibration on the film ruler. Simplified Ceph shows a millimetre reading only after the radiograph is calibrated.
Reference values come from particular samples. Most reference values come from specific study groups, so read them with the patient’s age, sex and ethnic background in mind.
Check your own error. Tracing a few films again after a while shows how far your own points move [4].
Description, not decision. This article describes the measurements. It does not cover diagnosis or treatment planning.

Do this in Simplified Ceph

Simplified Ceph includes the McNamara analysis: the nasion perpendicular, effective jaw lengths, and the upper and lower pharynx. You place the landmarks on a lateral cephalogram, and the readings update as you go. Simplified Ceph shows the published reference value next to each reading. There is a Free plan for lateral cephalometric analysis.

Open Simplified Ceph About Simplified Ceph

Educational content for clinicians and students. Reference values vary between populations. This page does not replace clinical judgement.

References

McNamara JA Jr. A method of cephalometric evaluation. Am J Orthod. 1984;86(6):449-469. doi: 10.1016/S0002-9416(84)90352-X. PMID: 6594933
Jacobson A, Jacobson RL, eds. Radiographic Cephalometry: From Basics to 3-D Imaging. 2nd ed. Chicago: Quintessence; 2006. ISBN 978-0-86715-461-0.
Baumrind S, Frantz RC. The reliability of head film measurements. 1. Landmark identification. Am J Orthod. 1971;60(2):111-127. PMID: 5283996.
Houston WJB. The analysis of errors in orthodontic measurements. Am J Orthod. 1983;83(5):382-390. doi:10.1016/0002-9416(83)90322-6.