Plagiocephaly Calculator (CVAI & Cephalic Index)
Calculate the cranial vault asymmetry index (CVAI) and cephalic index from your baby’s head measurements to grade flat head syndrome (plagiocephaly and brachycephaly) severity.
How it works
CVAI = (longer diagonal − shorter diagonal) ÷ shorter diagonal × 100 · cephalic index = head width ÷ head length × 100 · CVAI levels: < 3.5%, 3.5–6.25%, 6.25–8.75%, 8.75–11%, > 11%
Positional (deformational) plagiocephaly is a flattening of one side of the back of the head, common in babies who sleep on their backs. Clinicians measure the two cranial diagonals with calipers or a 3D scan; the cranial vault asymmetry index (CVAI) expresses their difference as a percentage, and the Children’s Healthcare of Atlanta scale grades it from level 1 (normal) to level 5 (very severe). The cephalic index compares width with length: 75–85% is the usual range, above 85% suggests brachycephaly (flat back of the head) and below 75% dolichocephaly. Mild cases improve with repositioning and tummy time; helmets are reserved for more severe or persistent cases after about 4–6 months of age.
Worked example
Diagonals of 140 mm and 132 mm: CVAI = (140 − 132) ÷ 132 × 100 = 6.1%, which is Level 2 — mild (repositioning and tummy time). With a width of 118 mm and a length of 142 mm the cephalic index is 118 ÷ 142 × 100 = 83.1% — normal proportions.
Sources: Holowka MA et al. (2017) Plagiocephaly severity scale to aid in the clinical treatment of infants (Children’s Healthcare of Atlanta). Cleft Palate Craniofac J 54(4):389–396 · AAP Clinical Report: Prevention and management of positional skull deformities in infants (2011, reaffirmed)
Frequently asked questions
What CVAI is considered plagiocephaly?
On the Children’s Healthcare of Atlanta scale, a CVAI under 3.5% is within normal limits, 3.5–6.25% is mild, 6.25–8.75% moderate, 8.75–11% severe and over 11% very severe plagiocephaly.
When is a helmet recommended?
Helmets (cranial orthoses) are usually considered for moderate cases that do not improve with repositioning and for severe or very severe cases, ideally starting between about 4 and 6 months when the skull grows fastest.
How can I prevent a flat head?
Always put your baby to sleep on the back, but alternate the direction the head faces, give plenty of supervised tummy time while awake, limit time in car seats and bouncers and hold your baby upright often.
Can I measure the diagonals at home?
Home measurements with a tape are not precise enough to grade severity. Pediatricians and orthotists use calipers or 3D scans; use this calculator with those measurements and ask your pediatrician if you notice flattening.
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This calculator gives general guidance and is not a diagnosis or medical advice. If you are worried about your child, or they seem unwell, contact your pediatrician, a health center or emergency services.