Sex
Unknown
Gestational age
wks
Abdominal Circumference
mm
Head Circumference
mm
Biparietal Diameter
mm
Femur Length
mm
Result
Estimated fetal weight
g
Your baby is in the 50th percentile! 👶
✅ Your baby's weight is within normal range.
    • Y axis: fetal weight in grams (g).
    • X axis: gestational age in weeks.

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 WHO multinational growth charts. 👶👶🏾👶🏽👶🏻

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 2-year 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:

  1. Small for the gestational age (age of the pregnancy, counted from the conception)
  2. 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.)

  • 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.

You've learned everything about fetal weight percentiles - go on and check our other percentile-themed tools:

How to use the fetal weight percentile calculator?

Our estimated fetal weight percentile calculator needs just a few easy steps:

  1. Enter the gender of your baby

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

  2. Enter the gestational age

    This calculator is for fetuses older than 14 weeks. (We use a different type of measurement in younger pregnancies: the Crown-rump length (CRL)).

  3. 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
2.5510255075909597.5
14707378839098104109113
15899399106114124132138144
16113117124133144155166174181
17141146155166179193207217225
18174181192206222239255268278
19214223235252272292313328340
20260271286307330355380399413
21314327345370398428458481497
22375392412443476512548575595
23445465489525565608650682705
24523548576618665715765803830
25611641673723778836894938970
267077437808389029711,0381,0871,125
278138558989641,0391,1181,1961,2511,295
289299771,0261,1021,1891,2791,3681,4291,481
291,0531,1081,1651,2511,3501,4531,5541,6221,682
301,1851,2471,3131,4101,5231,6401,7531,8281,897
311,3261,3941,4701,5791,7071,8381,9642,0462,126
321,4731,5481,6351,7571,9012,0472,1872,2762,367
331,6261,7081,8071,9422,1032,2662,4192,5162,619
341,7851,8721,9852,1342,3122,4922,6592,7642,880
351,9482,0382,1672,3302,5272,7232,9043,0183,148
362,1132,2052,3522,5312,7452,9593,1533,2773,422
372,2802,3722,5372,7332,9663,1953,4033,5383,697
382,4462,5362,7232,9353,1863,4323,6523,7993,973
392,6122,6962,9053,1353,4033,6643,8974,0584,247
402,7752,8493,0843,3333,6173,8924,1354,3124,515

Along with monitoring the baby's growth and weight, we can also check if the mother's pregnancy weight gain is also within a healthy range. 🤰

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:

log10(Fetal weight) = 1.3596 - (0.00386 * AC * FL) + (0.0064 * HC) + (0.00061 * BPD * AC) + (0.0424 * AC) + (0.174 * FL),

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); and
  • log10(Fetal weight) means the fetal weightlogarithm 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.
Łucja Zaborowska