A Crown Rump Length (CRL) Calculator helps estimate gestational age based on the measurement of the fetus from the top of the head (crown) to the bottom of the torso (rump). This measurement is commonly used in early pregnancy ultrasounds, typically between 6 and 14 weeks of gestation, to determine the fetal age and expected due date.
Medical professionals use CRL calculations because fetal growth during early pregnancy follows a predictable pattern. The CRL is considered one of the most accurate methods for dating a pregnancy before the second trimester. By using this calculator, expectant parents and healthcare providers can determine gestational age with a high degree of accuracy.
Formula of Crown Rump Length Calculator
There is no single universal formula for converting Crown Rump Length (CRL) to gestational age, but an approximation used in many medical studies is:
Where:
- CRL is measured in millimeters (mm).
- Gestational Age is the age of the fetus in weeks.
This formula provides an estimate, but actual gestational age can vary based on fetal growth patterns.
Pre-Calculated Crown Rump Length Table
For convenience, the table below provides an estimated correlation between CRL and gestational age:
| Gestational Age (Weeks) | Approximate CRL (mm) |
|---|---|
| 6 | 15 |
| 7 | 18 |
| 8 | 20 |
| 9 | 22 |
| 10 | 25 |
| 11 | 28 |
| 12 | 30 |
| 13 | 32 |
| 14 | 35 |
This table provides quick reference values without requiring manual calculations.
Example of Crown Rump Length Calculator
Let’s calculate the gestational age for a fetus with a Crown Rump Length (CRL) of 25 mm.
- Apply the formula:
- Gestational Age = CRL / 2.5
- Gestational Age = 25 / 2.5
- Gestational Age = 10 weeks
Thus, a fetus with a CRL of 25 mm is approximately 10 weeks gestational age.
Most Common FAQs
CRL is a highly accurate method for dating early pregnancy because fetal growth follows a predictable pattern during the first trimester.
Yes, while CRL provides a strong estimation, factors such as genetic variations and maternal health may cause slight differences in fetal growth.
A CRL measurement taken between 6 and 14 weeks is consider one of the most precise ways to estimate gestational age, with a margin of error of about 3 to 5 days.