CRL gestational age calculator
A CRL from 3 to 84 mm is the standard way to date a pregnancy in the first trimester; this converts it to weeks and a due date.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter crown-rump length (crl) and scan date.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Gestational age in days = 8.052 × √(CRL in mm) + 23.73 (Robinson and Fleming 1975). Whole completed days are used (rounded down); due date = scan date + (280 - age in days).
Example
Inputs: Crown-rump length (CRL) = 45 mm, Scan date = 2026-03-01. Result: Gestational age: 11 weeks; Gestational age in days: 77.7 days; Estimated due date: Sunday, September 20, 2026 (2026-09-20).
Limits and caveats
- Beyond 84 mm (about 14 weeks), head circumference and other measures replace CRL.
- CRL dating is accurate to within about 5 to 7 days and depends on a good measurement.
Questions about this tool
What does CRL mean?
It is the baby’s length from the top of the head to the bottom, measured on early scans before the legs make length hard to measure.
Why is my result a day off the scan report?
Some machines use newer charts such as INTERGROWTH, or round to the nearest day instead of down.
Will my doctor change the due date after a CRL scan?
If the period date and the CRL differ by more than a few days, doctors usually go with the scan date.