Calculate cephalic index from maximum head breadth and length, or solve for either measurement, with mm, cm, and inch conversions plus cautious shape references.
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Cephalic Index Formula
The cephalic index compares the maximum breadth of the head to the maximum length of the head. The result is expressed as a percentage.
- CI = cephalic index, expressed as a percentage
- B = maximum breadth of the head
- L = maximum length of the head
If you enter breadth and length, the calculator solves for cephalic index. Breadth and length must be in the same unit before the formula is applied. The calculator converts mm, cm, and inches internally so mixed units can be used.
- B = maximum breadth of the head
- CI = cephalic index
- L = maximum length of the head
If you enter cephalic index and length, the calculator rearranges the formula to solve for the missing breadth.
- L = maximum length of the head
- B = maximum breadth of the head
- CI = cephalic index
If you enter breadth and cephalic index, the calculator rearranges the formula to solve for the missing length.
Cephalic Index Categories
The calculator uses simplified historical adult descriptions: below 75, 75 to below 80, 80 to below 85, and 85 or greater. These contiguous boundaries are an implementation convention, not universal clinical cutoffs. Classification varies by age, sex, population and measurement method; these categories are not intended for infant assessment.
| Cephalic index | Category | General head shape description |
|---|---|---|
| Less than 75 | Dolichocephalic | Relatively long and narrow |
| 75 to below 80 | Mesocephalic | Intermediate proportions |
| 80 to below 85 | Brachycephalic | Relatively broad and short |
| 85 or greater | Hyperbrachycephalic | Very broad relative to length |
Length Unit Conversions Used
The calculator converts head breadth and head length to millimeters before applying the formula.
| Unit | Equivalent in millimeters |
|---|---|
| 1 mm | 1 mm |
| 1 cm | 10 mm |
| 1 inch | 25.4 mm |
Example Calculations
Example 1: Calculate cephalic index
Suppose the maximum breadth is 150 mm and the maximum length is 190 mm.
The cephalic index is 78.95%.
Example 2: Calculate missing head breadth
Suppose the cephalic index is 82 and the maximum length is 18 cm.
The maximum breadth is 14.76 cm.
FAQ
How do you measure head breadth and head length for cephalic index?
Maximum head breadth is the widest side-to-side measurement of the head. Maximum head length is the front-to-back measurement from the most prominent point of the forehead to the farthest point at the back of the head. Use the same measuring method for both values and keep the measuring tool level.
Does the cephalic index have units?
No. The cephalic index is a ratio multiplied by 100, so the length units cancel out. It is usually written as a percentage or as a plain index value. For example, 80% and 80 as an index value refer to the same calculation.
Can I enter breadth and length in different units?
Yes. The calculator converts the entered breadth and length to millimeters before calculating the result. For example, you can enter breadth in centimeters and length in millimeters, and the formula will still use consistent units internally.
