Crown-Rump Length Calculator

Enter your Crown-Rump Length (CRL) measurement in millimeters to estimate gestational age in weeks and days. The calculator uses the Robinson & Fleming formula to return your estimated gestational age and corresponding estimated due date (EDD) based on the CRL value from your ultrasound scan.

Disclaimer: This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions.

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Enter the CRL measurement from your ultrasound report (1–84 mm, typically weeks 6–14)

Enter the date the ultrasound scan was performed to calculate your estimated due date

Results

Estimated Gestational Age

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Weeks

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Extra Days

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Total Gestational Days

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Estimated Due Date (EDD)

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Frequently Asked Questions

What is Crown-Rump Length (CRL)?

Crown-Rump Length (CRL) is the measurement from the top of the embryo's head (crown) to the bottom of the buttocks (rump). It is the most accurate method of dating a pregnancy in the first trimester, typically measured between 6 and 14 weeks of gestation via ultrasound.

Which formula does this calculator use?

This calculator uses the Robinson & Fleming formula, one of the most widely accepted methods for estimating gestational age from CRL. The formula is: Gestational Age (days) = 8.052 × √(CRL + 1) + 23.73, where CRL is in millimeters.

What CRL range is valid for gestational age estimation?

The CRL measurement is most reliable between 1 mm and 84 mm, corresponding approximately to 6 to 14 weeks of gestational age. Beyond 84 mm (14 weeks), the fetus starts to curl and CRL becomes less accurate; other biometric measures like biparietal diameter (BPD) are used instead.

How accurate is CRL for dating a pregnancy?

CRL is considered the most accurate method for first-trimester pregnancy dating, with a margin of error of approximately ±3–5 days when measured between 6 and 12 weeks. Accuracy decreases slightly beyond 12 weeks as fetal position variability increases.

How is the Estimated Due Date (EDD) calculated?

The EDD is calculated by adding 280 days (40 weeks) to the estimated date of the last menstrual period (LMP). Using CRL, the calculator first determines gestational age in days, then subtracts that number of days from the scan date to find the equivalent LMP, and adds 280 days to get the EDD.

Can I use this calculator if I had IVF or a known conception date?

Yes, but the formula is calibrated for natural conception dating. In IVF pregnancies, embryo transfer age is typically already known precisely, so CRL-based dating may be used as a cross-check. Always consult your healthcare provider for official dating in assisted reproduction cases.

Is CRL measurement the same as fetal size?

CRL reflects gestational age, not necessarily fetal weight or health. While CRL gives a reliable age estimate in early pregnancy, it should not be used alone to assess fetal growth. Your healthcare provider will use multiple measurements over the pregnancy to monitor growth.

Should I use this calculator instead of my doctor's assessment?

No. This tool is for educational and informational purposes only. Gestational age and due date should always be confirmed by a qualified healthcare professional using your full clinical picture, including ultrasound findings, last menstrual period, and medical history.