Crown-rump Length Calculator | CRL

Written by Great Medico

Updated September 24, 2026 •2 min read

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Pregnancy and fertility questions are full of dates, ranges, and probabilities—not certainties. Crown-rump Length Calculator | CRL narrows the question to the exact inputs shown and gives a practical estimate without pretending biology runs on a perfect calendar.

What this calculator does

Crown-rump Length Calculator | CRL uses Crown-rump length to calculate crown-rump length. It is built around the exact fields displayed in this plugin rather than a generic version of the topic. Where supported, it also shows Weeks + days so the primary result is easier to place in context. Pregnancy and fertility dates, hormone trends, and risk scores are estimates built around biologic averages. Cycle variation, ultrasound findings, assisted-reproduction details, and the individual pregnancy can matter more than a single calculated number.

How to use it

Enter or select Crown-rump length. Use the units offered by the calculator and choose the option that matches the actual clinical or timing situation. Check date entries and laboratory units before relying on the output. For paired dates or serial measurements, keep them within the same menstrual cycle, pregnancy, or treatment episode as the calculator requires.

How the calculation works

Gestational age is estimated from crown–rump length in millimeters with the implemented equation: days = 8.052 × √CRL + 23.73. The calculator divides by seven for gestational weeks and also displays the result as completed weeks plus additional days.

Example

Using the sample values prefilled in this calculator, the primary result is 9.69 weeks (Estimated gestational age) and Weeks + days is 9w 5d. This worked example shows how the plugin’s own default inputs flow through the implemented method; replace them with the correct patient, laboratory, imaging, or personal values before interpreting a result.

How to interpret the result

Treat the output as estimated gestational age based on the assumptions encoded in this calculator. It can help with planning or understanding a measurement, but pregnancy and reproductive biology vary enough that the calculated date, ratio, or probability should be seen as a range or estimate rather than a guarantee.

Limitations and notes

CRL is most useful for first-trimester dating when measured correctly on ultrasound. The formula is not intended for later gestation or poor-quality/off-axis measurements. Obstetric dating should follow the ultrasound method and redating thresholds used by the clinician rather than a standalone web calculation.