About
About CrLage Calculator
Clinical reference tools for first-trimester ultrasound dating, built on peer-reviewed research and designed for point-of-care use.
Our Purpose
CrLage Calculator was developed to provide healthcare professionals with a fast, reliable, and evidence-based tool for converting crown-rump length (CRL) measurements to gestational age. Accurate first-trimester dating is one of the most critical steps in obstetric care, influencing everything from due date assignment to the timing of screening tests and interventions.
The Robinson and Fleming (1975) formula remains one of the most widely validated methods for CRL-based gestational age estimation. By implementing this formula alongside modern reference standards, we aim to reduce calculation errors and support consistent clinical decision-making.
Clinical Standards
All calculations on this platform follow the established formula: GA (days) = 8.052 × √(CRL) + 23.73, as published by Robinson and Fleming in the British Journal of Obstetrics and Gynaecology (1975). The valid range for this formula is 7–95 mm CRL, corresponding to approximately 6–14 weeks of gestation.
We regularly review the published literature to ensure our reference data, accuracy ranges, and clinical guidance remain current. Where multiple evidence sources exist, we prioritize systematic reviews and large-cohort validation studies.
Who This Is For
CrLage Calculator is designed for obstetricians, midwives, radiologists, sonographers, and other healthcare professionals involved in first-trimester ultrasound assessment. The tools support clinical workflow by eliminating manual calculation steps and reducing the risk of arithmetic error.
Students and educators in medical ultrasound programs may also find the reference tables and growth charts valuable for teaching and learning.
Accuracy & Limitations
While the Robinson and Fleming formula has been validated across diverse populations, no single formula achieves perfect accuracy for every pregnancy. Factors such as maternal age, fetal position, measurement technique, and biological variation all influence the relationship between CRL and gestational age.
We provide accuracy ranges and confidence intervals alongside every calculated result. These estimates should be interpreted in the context of the full clinical picture, including the patient’s menstrual history, other ultrasound findings, and serial measurements when available.
Our Commitment
We are committed to transparency in our methodology, clarity in our disclaimers, and respect for the responsibility that healthcare professionals bear in clinical decision-making. No tool replaces clinical judgment, and we encourage all users to verify critical results against primary sources and institutional protocols.
For questions, suggestions, or to report an issue, please contact us. For information on appropriate use of this site, see our Disclaimer and Medical Disclaimer.