CRL Calculator

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CRL calculator

Estimate gestational age and due date from a first-trimester crown-rump length measurement, using the Robinson & Fleming formula.

Most reliable between 10 mm and 84 mm (roughly 6+0 to 13+6 weeks).
Date the ultrasound measurement was taken.
This measurement is outside the range where the Robinson & Fleming formula has been validated. Treat this estimate with caution and consider dating by a later biometry scan.
Formula: gestational age (days) = 8.052 × √(CRL in mm) + 23.73 (Robinson & Fleming, 1975). Due date is calculated as 280 days from the estimated last menstrual period implied by this gestational age.
Gestational age
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enter CRL and scan date
Estimated due date
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based on 280-day pregnancy

For clinical support, not diagnosis. Dating accuracy depends on correct measurement technique and a genuine mid-sagittal, neutral-position image. If CRL-based dating differs substantially from menstrual dating, ultrasound dating is generally preferred in the first trimester, per standard obstetric practice — confirm locally applicable guidance with your care team.

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