Crown-Rump Length (CRL) Calculator

Your details

Choose which value you want to find.
Unit used for the CRL measurement on your scan report.
Crown-rump length from the ultrasound report. Typical range 4-90 mm (weeks 6-14).
mm
Enter the date of the ultrasound scan to calculate your estimated due date.
Gestational ageOptimal dating window
74days

Estimated gestational age (Robinson and Fleming equation)

Gestational age10 weeks + 4 days
Expected CRL38mm
Dating accuracyWithin optimal 6-14 week window: accurate to approx. +/- 3-5 days.
74 days gestation
  • 6 weeks
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  • 10 weeks
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  • 14 weeks

Estimated gestational age: 10 weeks + 4 days

  • A CRL of 38 mm corresponds to a gestational age of 10 weeks + 4 days by the Robinson and Fleming equation.
  • First-trimester CRL dating is accurate to within 3-5 days and is more reliable than last menstrual period (LMP) dating, which can be off by 1-2 weeks.
  • CRL measurement accuracy depends on fetal position and sonographer technique. Always discuss results with your healthcare provider.

Next stepA dating scan in the first trimester is the most accurate way to confirm your due date. A second-trimester anomaly scan at 18-22 weeks checks fetal development.

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