Crown-Rump Length Calculator
CRL to Gestational Age
Convert crown-rump length to estimated gestational age
mm
Gestational Age to Expected CRL
Estimate expected CRL from known gestational age
weeks
days
Formula
Robinson & Fleming: GA (days) = 8.052 x sqrt(CRL_mm x 1.037) + 23.73 | Inverse: CRL = ((GA_days - 23.73) / 8.052)^2 / 1.037 | Due Date = 280 - GA_days remaining
Frequently Asked Questions
What is Crown-Rump Length (CRL)?
CRL is the measurement from the top of the embryo's head (crown) to the bottom of its buttocks (rump). It is measured by ultrasound and is the most accurate method for dating a pregnancy during the first trimester (7-13 weeks).
How accurate is CRL for dating pregnancy?
CRL dating in the first trimester is accurate to within 3-5 days (compared to 7-14 days for second trimester measurements). This is why first trimester ultrasound is preferred for establishing the due date.
What if CRL is smaller than expected?
A CRL smaller than expected could mean the pregnancy is earlier than thought, or it could indicate a growth concern. A single measurement may not be conclusive — your doctor may recommend a follow-up ultrasound in 1-2 weeks to assess growth.
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