Fetal Weight Percentile Calculator
Our fetal weight percentile calculator computes your child's growth and compares it to the general population. Our BPD, HC, AC, and FL calculator uses all the necessary ultrasound fetal measurements to compute your child's weight at a given week of the pregnancy.
We use the Hadlock equation and
. 👶👶🏾👶🏽👶🏻Want to know more? Follow the article below to discover fetal weight percentile chart by week, and details of our baby weight predictor calculator. We'll also cover the baby percentiles during pregnancy as well as the SGA and LGA definitions.
What percentile is my baby, and what does it mean?
We use percentiles to measure values that are extremely variable in the population  especially in children. For example, we can't give a precise value of height that a healthy 2year old boy should achieve  it all depends on his individual and genetic characteristics. 🔬
However, doctors love all the hard data and numbers that help them make critical clinical decisions. They needed a tool that allows quick and precise evaluation of their patients.
So how did we tackle this problem? 🤔
Percentiles are a great solution! Instead of giving us a precise number, they inform us about the range in which your baby's height or weight should fall. Thanks to percentiles, we can tell how your child's health looks when compared to the general population and detect any significant abnormalities.
When we talk about fetal weight abnormalities, two most important definitions come to mind:
 Small for the gestational age (age of the pregnancy, counted from the conception; to calculate it, you can use gestational age calculator); and
 Large for the gestational age.
💡 SGA  Small for Gestational Age babies are all babies that fall below the 10th percentile of the population, when it comes to their EFW percentile. It means that over 90% of the population grew larger than they did.
💡 LGA  Large for Gestational Age babies exceed the 90th percentile of their Estimated Fetal Weight. It means that only 10% of population is larger than them.
These two explanations are based on an Estimated Fetal Weight (EFW) calculations that use the ultrasound technique to evaluate a baby's weight inside its mother's uterus.
To estimate the fetal weight, we use the following measurements:

Abdominal circumference  circumference of the baby's belly, measured at the liver's height. (Advanced: an umbilical portion of the left portal vein should be in the center of the abdomen.)

Head circumference measured at the point where specific brain structures are visible. (Advanced: plane that traverses the thalami and cavum septum pellucidum.) To check where the newborn's head circumference places amongst their peers, use head circumference percentile calculator.

Biparietal diameter  length of a distance between two parietal bones of a baby's skull.

Femur length  a length of the baby's thigh bone.
Our fetal growth calculator uses all four of the enumerated measurements; additionally, we can also measure the humerus length.
💡 We could also measure the estimated fetal weight by assessing the fundal height  this method, however, is not as accurate. To learn more about the concept, visit fundal height calculator.
How to use the fetal weight percentile calculator?
Our estimated fetal weight percentile calculator needs just a few easy steps:

Enter the gender of your baby
Be specific; if you already know the baby's gender, reveal it. 🎉

Enter the gestational age
This calculator is for fetuses older than 14 weeks. (We use a different type of measurement in younger pregnancies: the Crownrump length (CRL)).

Find all the enumerated ultrasound measurements
Remember to choose the correct unit  imperial or metric.
🔅 Our tool also works as a large and small for gestational age calculator: along with the results, you will receive feedback concerning your child's weight's location on the chart and its meaning. Read more about LGA/SGA in the section above.
Fetal growth chart
Here you can find the fetal weight week by week for the fetuses of an unknown gender ♀️/♂️:
Gestational Age (weeks)  Estimated Fetal Weight (g) by percentile  

2.5  5  10  25  50  75  90  95  97.5  
14  70  73  78  83  90  98  104  109  113 
15  89  93  99  106  114  124  132  138  144 
16  113  117  124  133  144  155  166  174  181 
17  141  146  155  166  179  193  207  217  225 
18  174  181  192  206  222  239  255  268  278 
19  214  223  235  252  272  292  313  328  340 
20  260  271  286  307  330  355  380  399  413 
21  314  327  345  370  398  428  458  481  497 
22  375  392  412  443  476  512  548  575  595 
23  445  465  489  525  565  608  650  682  705 
24  523  548  576  618  665  715  765  803  830 
25  611  641  673  723  778  836  894  938  970 
26  707  743  780  838  902  971  1,038  1,087  1,125 
27  813  855  898  964  1,039  1,118  1,196  1,251  1,295 
28  929  977  1,026  1,102  1,189  1,279  1,368  1,429  1,481 
29  1,053  1,108  1,165  1,251  1,350  1,453  1,554  1,622  1,682 
30  1,185  1,247  1,313  1,410  1,523  1,640  1,753  1,828  1,897 
31  1,326  1,394  1,470  1,579  1,707  1,838  1,964  2,046  2,126 
32  1,473  1,548  1,635  1,757  1,901  2,047  2,187  2,276  2,367 
33  1,626  1,708  1,807  1,942  2,103  2,266  2,419  2,516  2,619 
34  1,785  1,872  1,985  2,134  2,312  2,492  2,659  2,764  2,880 
35  1,948  2,038  2,167  2,330  2,527  2,723  2,904  3,018  3,148 
36  2,113  2,205  2,352  2,531  2,745  2,959  3,153  3,277  3,422 
37  2,280  2,372  2,537  2,733  2,966  3,195  3,403  3,538  3,697 
38  2,446  2,536  2,723  2,935  3,186  3,432  3,652  3,799  3,973 
39  2,612  2,696  2,905  3,135  3,403  3,664  3,897  4,058  4,247 
40  2,775  2,849  3,084  3,333  3,617  3,892  4,135  4,312  4,515 
How to calculate the fetal weight percentile?
It's easier than you think!
1. Calculate the weight of the fetus 📉
Our fetal percentile calculator faciliates the process of computing the fetus weight, based on the ultrasound measurements; however, if you'd like to calculate it yourself, you're more than welcome to try the equation we used:
where:
Fetal weight
is given in grams (g);AC
means the Abdominal Circumference and is given in centimeters (cm);FL
means the Femur Length and is given in centimeters (cm);HC
means the Head Circumference and is given in centimeters (cm);BPD
means the Biparietal Diameter and is given in centimeters (cm); andlog₁₀(Fetal weight)
means the fetal weight logarithm of the base of 10.
2. Find the percentile 📈
When you already know the fetus's weight, all you need to do is check the fetal growth charts or tables for a given gestational age.
 Find your baby's gestational age on the bottom of the page: draw a vertical line starting from that point.
 Find its weight on the left or right edge of the chart, and draw a horizontal line beginning from that point.
 Mark the crossing of these two lines with a dot.
 Check which fetal weight percentile line on the chart is located the closest to the dot you've just drawn.
❗ Our birth weight calculator for the US is a tool prepared for measuring children of different ethinicites  despite that fact, you shouldn't use it as a single source of clinical knowledge. Always consult your doctor, and double check any measurements that may have any impact on clinical practice.
FAQ
What is a percentile?
A percentile is a score used in statistics and medicine to indicate where a certain measurement places among the same measurement in its peers.
When we say that a measurement belongs to the kth
percentile, we mean that k %
of the measurements in a population are below the one we are considering. Percentiles are largely used when assessing widely variable quantities, like the heights and weights of individuals.
What is the estimated fetal weight?
The estimated fetal weight is the baby's weight at a specific time of the pregnancy. Because the measurement cannot be taken directly, it is estimated using an ultrasound scan, which finds:
 Abdominal and head circumference (
AC
andHC
);  Biparietal diameter (the distance between parietal bones in the skull) (
BPD
); and  Femur length (occasionally also humerus length) (
HL
).
Plug those measurements in the following formula to find the estimated fetal weight:
log₁₀(Fetal weight) = 1.3596  (0.00386 × AC × FL) + (0.0064 × HC) + (0.00061 × BPD × AC) + (0.0424 × AC) + (0.174 × FL)
.
How do I find the fetal weight percentile?
To find the fetal weight percentile, follow these steps:
 Calculate the estimated fetal weight.
 On a fetal weight percentile chart, find the intersection between the value of the estimated fetal weight and the gestational age.
 The intersection will fall close to a line on the graph: each line is associated with a specific percentile, which in this case, corresponds to your baby's percentile.
Which percentile is a fetus with estimated fetal weight 250 g at 18 weeks?
75ᵗʰ
percentile. To calculate the percentile, find a fetal weight percentile chart and find the intersection between the lines corresponding to the values:
 Estimated fetal weight
250 g
; and  Gestational age
18 weeks
.
The closest line to the point is the 75ᵗʰ
percentile, which means that the baby is heavier than 75% of all other babies the same age.
 Y axis: fetal weight in grams (g).
 X axis: gestational age in weeks.