Crown Rump Length Calculator

The crown-rump length calculator is one of the most accurate ways to calculate gestational age in weeks.

It is a significant determinant of gestational age between 6 to 13 weeks. This article will cover CRL’s definition, the CRL’s measuring chart, and how to determine gestational age using CRL.

What’s a crown rump length?

The crown-rump length helps calculate the length of human embryos and fetuses. The distance is measured from the crown (the top of the head) to the rump (the bottom of the buttocks).

It is usually derived from ultrasound images and can be used to gauge gestational age. After 10 gestational weeks or 71 completed days based on the last menstrual period (LMP), the embryo develops into a fetus.

A strong association between the CRL measurement and fetal age during a time of rapid growth with no influence from fetal pathology is required for the CRL to be accurate in timing the pregnancy.

Why is Crown-rump length measured?

CRL measurement is the most accurate method of determining your baby’s age; the doctor should always match it to the date of your LMP. Besides determining the gestational age, CRL can be used to estimate the expected delivery date (EDD).

Because newborns grow at varying rates, gestational age is only just an estimate. When biological variability is at its lowest early in pregnancy, CRL is most accurate.

Head circumference measurements, femur length, and biparietal diameter assess the baby’s development once it has passed the 14-week mark. The umbilical cord and CRL are usually the same length throughout the pregnancy.

The accuracy of the baby’s gestational age will increase with the timing of the first ultrasound. Therefore, you should aim to check the CRL measurement early in your pregnancy.

Uses of CRL

Below are some of the uses of CRL:

  1. It serves as the main gauge for determining gestational age between 6 and 13 weeks.
  2. Missed miscarriage: An ultrasound should show a heartbeat once the fetus’s CRL exceeds 7 millimeters. The pregnancy is most likely a missed miscarriage if no heartbeat or cardiac activity is found. Missed or silent miscarriages frequently happen without the common miscarriage signs and symptoms because the placenta can continue producing hormones that conceal the visible signs of a miscarriage.

How to use CRL and ultrasound to determine the baby’s age?

Following a positive pregnancy test, you should see your OB-GYN and gynecologist to determine how far along the pregnancy is.

In the early stages of pregnancy, your doctor will:

  • Inquire as to when your most recent menstruation began.
  • Will measure your CRL and compare it to a chart of crown-rump lengths using ultrasound technology.
  • Conduct a thorough physical examination and take a detailed history.

If your pregnancy is further along:

  • Your doctor will inquire about your last period;
  • Using ultrasound technology, your doctor will measure your unborn child’s head, bones, and tummy. The fetal weight percentile tool will be used to calculate these figures.
  • Your doctor will do a comprehensive physical examination and take the medical history.

Then, using specialized algorithms (often included in the ultrasound machine), all this data is calculated, and the results are compared to the date of your most recent menstrual cycle.


  • First-trimester measures are used to calculate the baby’s age and the expected date of birth.
  • Measurements taken throughout the second and third trimesters are used to evaluate the baby’s development and general health and rule out any potential disorders or anomalies.

How to use the Crown-rump length calculator?

This calculator will assist you in calculating the gestational age from CRL. The CRL calculator is quite simple to use! It provides you with a clear solution to your query.

  • Enter your CRL measurements into the appropriate field.
  • Wait for your result, which will be displayed in hours, days, weeks, or mixed format.

How can I calculate the gestational age using crown-rump length?

  1. Select the equation that works best for you: There are several different formulas that are available for calculating fetal age. This formula is based on the Robinson and Fleming equation; It’s one of the simplest formulas discovered: Gestational age (in days) = 8.052 * √(CRL * 1.037) + 23.73.


CRL is measured in millimeters (mm).

  • Utilizing a unique CRL measurement chart is another choice. It is unquestionably less complicated than calculations, but it is still more challenging than utilizing a crown-rump length calculator.
CRL (mm)ofGestational age (weeks+days)


What is the typical length of the crown-rump?

At the onset of the sixth week, when the CRL is 1.5 to 3 mm, according to standard texts on embryology, the embryonic heart starts to beat. Consequently, it is not surprising that heart activity may or may not be seen in normal embryos with CRL less than 2 mm.

Does CRL vary between boys and girls?

The mean CRL was substantially higher in male than female fetuses, according to a general linear model adjusted for gestational age (40-50 days).

Do male fetuses grow faster?

Boys grow more quickly than girls in the womb, which puts them at higher risk of malnutrition. Small stature at birth and later cardiovascular diseases, such as hypertension, are caused by fetal undernutrition.

Can you determine if it’s a boy or a girl at 12 weeks?

After nine weeks, the gender can be determined via blood testing to check for specific diseases. Based on the position of the genital tubercle at 12 weeks, we might be able to utilize ultrasound to identify the gender.


From 6 to 13 weeks of pregnancy, the Crown Rump Length (CRL) can be measured. The measurement may change somewhat if the fetus is momentarily stretching or straightening its body. CRL is the primary indicator of gestational age, and an ultrasonic scan is used to take the measurement.

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