Crown Rump Length Calculator

Femur Length (FL):

Gestational Age (GA in weeks):

Calculate

Crown Rump Length (CRL):

The Crown Rump Length (CRL) Calculator is a valuable tool used in obstetrics to estimate the length of a fetus from the top of the head (crown) to the bottom of the torso (rump). This measurement is crucial during early pregnancy scans and helps assess the growth and development of the fetus.

Formula
The formula used to calculate Crown Rump Length is:
CRL = (Femur Length × Gestational Age) divided by 7, then add 42.
In simpler terms: CRL = (FL × GA) / 7 + 42

How to Use

1. Enter the femur length (FL) in millimeters.
2. Input the gestational age (GA) in weeks.
3. Click the “Calculate” button.
4. The Crown Rump Length (CRL) will be displayed instantly.

Example
If the femur length is 15 mm and the gestational age is 20 weeks, then:
CRL = (15 × 20) / 7 + 42 = 300 / 7 + 42 ≈ 85 mm.
So, the estimated CRL is approximately 85 mm.

FAQs

1. What is the Crown Rump Length (CRL)?
   It is the measurement from the top of the fetus’s head to the bottom of its torso, excluding the legs.
2. Why is CRL important?
   It helps estimate gestational age and monitor fetal development during early pregnancy.
3. What units should be used in this calculator?
   Femur length should be in millimeters, and gestational age in weeks.
4. Is this calculator accurate?
   It provides an estimate based on a widely accepted formula, but clinical evaluation should follow.
5. Can I use this calculator at home?
   Yes, if you have access to the required data from a scan or report.
6. What does a high CRL indicate?
   It may suggest that the fetus is larger than average for its gestational age.
7. What does a low CRL indicate?
   It could indicate delayed fetal growth or incorrect gestational age estimation.
8. Is CRL the only measurement used during pregnancy?
   No, other measurements include head circumference, biparietal diameter, and abdominal circumference.
9. When is CRL most reliable?
   During the first trimester (up to 13 weeks), CRL is the most accurate indicator of gestational age.
10. Can I use this for twins?
    Yes, but CRL should be calculated for each fetus separately.
11. What is a normal CRL at 12 weeks?
    Around 55–65 mm, though it can vary.
12. How is femur length measured?
    It is measured using ultrasound imaging by a trained technician.
13. Can this calculator detect abnormalities?
    No, it only estimates size. Abnormalities require clinical diagnosis and imaging.
14. What if the calculator gives a much higher or lower CRL than expected?
    Recheck your inputs and consult your healthcare provider for interpretation.
15. Do I need to convert units?
    Ensure your inputs are consistent—femur length in millimeters and gestational age in weeks.
16. Is this calculator suitable for veterinary use?
    No, this calculator is specifically for human fetal development.
17. Does maternal health affect CRL?
    Yes, maternal health and nutrition can influence fetal development and CRL.
18. Is the CRL used in dating scans?
    Yes, it is the primary parameter used in early dating scans.
19. Can CRL predict the baby’s gender?
    No, CRL is unrelated to fetal sex.
20. How often should CRL be measured?
    Typically once in the first trimester, unless additional monitoring is needed.

Conclusion
The Crown Rump Length Calculator is a practical tool for estimating fetal size and assessing growth during early pregnancy. While it provides a quick estimate, it should complement professional ultrasound evaluation and medical advice. Whether you’re a medical professional or an expectant parent, understanding CRL offers valuable insight into prenatal development.