CVAI calculator: measure your baby's head asymmetry with two diagonals
CVAI (Cranial Vault Asymmetry Index) is the most widely used numerical measure of flattening in an infant's head. Enter the two diagonals, get the value and take it to your clinician.
Upload a 3D scan
STL, PLY or OBJ head scan. The file is processed in your browser and never sent to a server.
Enter the measurements
Optional: cephalic index
The cephalic index is the width-to-length ratio of the head. Higher values can indicate brachycephaly (flattening at the back), lower values dolichocephaly; which value counts as typical depends on the baby's age and the reference used.
How to measure and calculate CVAI
- 1With your baby calm, position yourself so you look down at the top of the head.
- 2Run a flexible tape diagonally from just above one eyebrow to behind the opposite ear (Diagonal A).
- 3Repeat the same measurement in the other direction (Diagonal B).
- 4Enter both values in millimetres.
Result
Enter both diagonals to see the result.
Levels: Children's Healthcare of Atlanta plagiocephaly severity scale. Source: Holowka MA et al. Plagiocephaly Severity Scale to Aid in Clinical Treatment Recommendations. J Craniofac Surg. 2017;28(3):717–722. doi:10.1097/SCS.0000000000003520
This is not a diagnostic tool
This calculator is for information only. Measurements taken at home with a tape measure are not of clinical accuracy and cannot be used to make a diagnosis on their own. Decisions about head shape, development or treatment can only be made by the doctor or orthotist who examines your baby.
Why timing matters
The most effective period for head shape treatment is roughly between the 4th and 8th month, when the skull grows fastest and is most responsive to reshaping. If you have a concern, an early assessment keeps more options open.
Who are you?
Talk the result through with a specialist
Write to us; if there is a clinic working with Clonify in your area, we'll point you to it. Your result is added to the form automatically.
Result added to the form
No calculated result yet — you can still send the form.
Frequently asked questions
What is CVAI?
CVAI (Cranial Vault Asymmetry Index) quantifies asymmetry in an infant's head. It is calculated from two diagonals taken at roughly 30 degrees from the anterior-posterior axis: the difference between them divided by the longer diagonal, expressed as a percentage.
How is CVAI calculated?
CVAI = (longer diagonal − shorter diagonal) ÷ longer diagonal × 100. For example, with diagonals of 145 mm and 133 mm the difference is 12 mm and CVAI is about 8.3%.
What CVAI value is considered normal?
On the Children's Healthcare of Atlanta plagiocephaly severity scale (Holowka et al., J Craniofac Surg 2017), CVAI below 3.5% is Level 1 (within normal limits), 3.5–6.25% Level 2, 6.25–8.75% Level 3, 8.75–11% Level 4 and above 11% Level 5. The level only locates the value; assessment requires a clinical examination and accurate measurement.
What is the cephalic index?
The cephalic index is head width divided by head length × 100. Higher values can point toward brachycephaly and lower values toward dolichocephaly; what counts as typical depends on the baby's age and the reference used.
Can CVAI be calculated from a 3D scan file?
Yes. When you upload an STL, PLY or OBJ head scan, the tool finds the widest horizontal slice of the head, determines the anterior-posterior axis and measures the diagonals at ±30° from it. The file is processed in your browser and never sent to a server. You can adjust the slice height and axis angle manually.
Can I measure my baby's head at home?
A flexible tape measure can give you an idea, but home measurements are not of clinical accuracy and cannot be used for diagnosis. If the result worries you, see a doctor or an orthotist.