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Calculator: Head circumference-for-age percentiles and Z-scores, 0 to 24 months (WHO)

Calculator: Head circumference-for-age percentiles and Z-scores, 0 to 24 months (WHO)

 
Input
 
Sex Female

 Male
Age  
Head circumference  

 
Results
 
Important: Inputs must be complete to perform calculation.

 
 
Z-score    
Percentile    
 
Decimal precision  
 

 

 
Head circumference-for-age percentile interpretation

 
Percentile <2: Microcephaly
Percentile ≥2 and <98: Normal head circumference
Percentile ≥98: Macrocephaly

 
 

 
Notes
  • This calculator is based on the World Health Organization (WHO) growth standard.
  • Microcephaly is a head circumference greater than 2 standard deviations below the mean.
  • Macrocephaly is a head circumference greater than 2 standard deviations above the mean.
  • At the extremes (>97th percentile or <3rd percentile), small differences in percentiles represent clinically important differences. At these extremes, the Z-score is a more precise reflection of how far the measurement deviates from the mean and is a useful tool for tracking changes.
  • For all LMS tables, the row in the table corresponding to the patient-specific value is found in the first column of the table; values to be used for L (the Box-Cox power), M (the median), and S (the generalized coefficient of variation) in the equation for Z-score are retrieved.
  • The accuracy of the calculation can be assessed by viewing the graph of head circumference-for-age percentiles for this sex and age group in UpToDate.
  • Z-scores may be used to perform a table lookup for the corresponding percentile in the Normal table percentiles for Z-score table (below). Numbers along the left side (Y-axis) of the table represent the first number and first decimal place of the Z-score, while the numbers along the top (X-axis) of the table represent the second decimal position of the Z-score.

 
Equations used
 
Z_Score = ((Head_circumference/M)L - 1) / (L * S)
Percentile = ZtoPercentile(Z-score)

 

 
Examples
 
Z-scorePercentile equivalent
- 3.0
0.3
- 2.0
2.5
+ 2.0
97.5
+ 3.0
99.7

 
References
  1. World Health Organization. The WHO Child Growth Standards. https://www.who.int/childgrowth/standards/en/ (Accessed on June 26, 2023).

 
Appendix

 
LMS table: Head circumference-for-age percentiles, females 0 to 24 months, WHO growth standard
 
Age [months] Power [L] Median [M] Variation [S]
0 1 33.8787 0.0350
1 1 36.5463 0.0321
2 1 38.2521 0.0317
3 1 39.5328 0.0314
4 1 40.5817 0.0312
5 1 41.4590 0.0310
6 1 42.1995 0.0309
7 1 42.8290 0.0307
8 1 43.3671 0.0306
9 1 43.8300 0.0305
10 1 44.2319 0.0304
11 1 44.5844 0.0303
12 1 44.8965 0.0303
13 1 45.1752 0.0302
14 1 45.4265 0.0301
15 1 45.6551 0.0301
16 1 45.8650 0.0300
17 1 46.0598 0.0299
18 1 46.2424 0.0299
19 1 46.4152 0.0298
20 1 46.5801 0.0298
21 1 46.7384 0.0297
22 1 46.8913 0.0297
23 1 47.0391 0.0296
24 1 47.1822 0.0296

 
LMS table: Head circumference-for-age percentiles, males 0 to 24 months, WHO growth standard
 
Age [months] Power [L] Median [M] Variation [S]
0 1 34.4618 0.0369
1 1 37.2759 0.0313
2 1 39.1285 0.0300
3 1 40.5135 0.0292
4 1 41.6317 0.0287
5 1 42.5576 0.0284
6 1 43.3306 0.0282
7 1 43.9803 0.0280
8 1 44.5300 0.0280
9 1 44.9998 0.0279
10 1 45.4051 0.0279
11 1 45.7573 0.0279
12 1 46.0661 0.0279
13 1 46.3395 0.0279
14 1 46.5844 0.0279
15 1 46.8060 0.0279
16 1 47.0088 0.0279
17 1 47.1962 0.0280
18 1 47.3711 0.0280
19 1 47.5357 0.0280
20 1 47.6919 0.0281
21 1 47.8408 0.0281
22 1 47.9833 0.0281
23 1 48.1201 0.0282
24 1 48.2515 0.0282

 
LMS table: Normal table percentiles for Z-score
 
Z 1 3 5 7 9
-3.0 0.13% 0.12% 0.11% 0.11% 0.10%
-2.9 0.18% 0.17% 0.16% 0.15% 0.14%
-2.8 0.25% 0.23% 0.22% 0.21% 0.19%
-2.7 0.34% 0.32% 0.30% 0.28% 0.26%
-2.6 0.45% 0.43% 0.40% 0.38% 0.36%
-2.5 0.60% 0.57% 0.54% 0.51% 0.48%
-2.4 0.80% 0.75% 0.71% 0.68% 0.64%
-2.3 1.04% 0.99% 0.94% 0.89% 0.84%
-2.2 1.36% 1.29% 1.22% 1.16% 1.10%
-2.1 1.74% 1.66% 1.58% 1.50% 1.43%
-2.0 2.22% 2.12% 2.02% 1.92% 1.83%
-1.9 2.81% 2.68% 2.56% 2.44% 2.33%
-1.8 3.52% 3.36% 3.22% 3.07% 2.94%
-1.7 4.36% 4.18% 4.01% 3.84% 3.67%
-1.6 5.37% 5.16% 4.95% 4.75% 4.55%
-1.5 6.55% 6.30% 6.06% 5.82% 5.59%
-1.4 7.93% 7.64% 7.35% 7.08% 6.81%
-1.3 9.51% 9.18% 8.85% 8.53% 8.23%
-1.2 11.31% 10.94% 10.57% 10.20% 9.85%
-1.1 13.35% 12.92% 12.51% 12.10% 11.70%
-1.0 15.63% 15.15% 14.69% 14.23% 13.79%
-0.9 18.14% 17.62% 17.11% 16.60% 16.11%
-0.8 20.90% 20.33% 19.77% 19.22% 18.67%
-0.7 23.89% 23.27% 22.66% 22.07% 21.48%
-0.6 27.09% 26.44% 25.79% 25.14% 24.51%
-0.5 30.50% 29.81% 29.12% 28.43% 27.76%
-0.4 34.09% 33.36% 32.64% 31.92% 31.21%
-0.3 37.83% 37.07% 36.32% 35.57% 34.83%
-0.2 41.68% 40.91% 40.13% 39.36% 38.59%
-0.1 45.62% 44.83% 44.04% 43.25% 42.47%
-0.0 49.60% 48.80% 48.01% 47.21% 46.41%
0.0 50.40% 51.20% 51.99% 52.79% 53.59%
0.1 54.38% 55.17% 55.96% 56.75% 57.54%
0.2 58.32% 59.10% 59.87% 60.64% 61.41%
0.3 62.17% 62.93% 63.68% 64.43% 65.17%
0.4 65.91% 66.64% 67.36% 68.08% 68.79%
0.5 69.50% 70.19% 70.88% 71.57% 72.24%
0.6 72.91% 73.57% 74.22% 74.86% 75.49%
0.7 76.12% 76.73% 77.34% 77.94% 78.52%
0.8 79.10% 79.67% 80.23% 80.79% 81.33%
0.9 81.86% 82.38% 82.89% 83.40% 83.89%
1.0 84.38% 84.85% 85.31% 85.77% 86.21%
1.1 86.65% 87.08% 87.49% 87.90% 88.30%
1.2 88.69% 89.07% 89.44% 89.80% 90.15%
1.3 90.49% 90.82% 91.15% 91.47% 91.77%
1.4 92.07% 92.36% 92.65% 92.92% 93.19%
1.5 93.45% 93.70% 93.94% 94.18% 94.41%
1.6 94.63% 94.85% 95.05% 95.25% 95.45%
1.7 95.64% 95.82% 95.99% 96.16% 96.33%
1.8 96.49% 96.64% 96.78% 96.93% 97.06%
1.9 97.19% 97.32% 97.44% 97.56% 97.67%
2.0 97.78% 97.88% 97.98% 98.08% 98.17%
2.1 98.26% 98.34% 98.42% 98.50% 98.57%
2.2 98.65% 98.71% 98.78% 98.84% 98.90%
2.3 98.96% 99.01% 99.06% 99.11% 99.16%
2.4 99.20% 99.25% 99.29% 99.32% 99.36%
2.5 99.40% 99.43% 99.46% 99.49% 99.52%
2.6 99.55% 99.57% 99.60% 99.62% 99.64%
2.7 99.66% 99.68% 99.70% 99.72% 99.74%
2.8 99.75% 99.77% 99.78% 99.80% 99.81%
2.9 99.82% 99.83% 99.84% 99.85% 99.86%
3.0 99.87% 99.88% 99.89% 99.89% 99.90%

 
Only digits 0 to 9 and a single decimal point (".") are acceptable as numeric inputs. Attempted input of other characters into a numeric field may lead to an incorrect result.

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All information contained in and produced by the EBMcalc system is provided for educational purposes only. This information should not be used for the diagnosis or treatment of any health problem or disease. THIS INFORMATION IS NOT INTENDED TO REPLACE CLINICAL JUDGMENT OR GUIDE INDIVIDUAL PATIENT CARE IN ANY MANNER.

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