Calculator Inputs
Formula Used
The calculator uses a CRL based first trimester dating equation:
Gestational age in days = 8.052 × √CRL(mm) + 23.73
The result is rounded by your chosen rounding method. The due date is calculated as:
Estimated due date = Scan date + (280 - gestational age days)
The fetal age estimate is calculated as:
Fetal age estimate = Gestational age - 14 days
How to Use This Calculator
- Enter the crown rump length from the ultrasound report.
- Select millimeters or centimeters correctly.
- Choose the scan date used for the measurement.
- Add uncertainty if the measurement has a possible error range.
- Enter LMP or conception date only when comparison is needed.
- Press the calculate button to show results above the form.
- Use the CSV or PDF button to save the result.
Example Data Table
| CRL | Approximate Gestational Age | Common Use | Notes |
|---|---|---|---|
| 5 mm | 6 weeks 0 days | Early dating | Image quality matters greatly. |
| 10 mm | 7 weeks 0 days | Early confirmation | Check unit selection carefully. |
| 20 mm | 8 weeks 4 days | Routine dating | Useful for timeline planning. |
| 35 mm | 10 weeks 1 day | First trimester review | Compare with clinical dates. |
| 55 mm | 11 weeks 6 days | Screening preparation | Confirm with report findings. |
| 75 mm | 13 weeks 2 days | Late first trimester | Dating rules may vary locally. |
CRL Dating in Early Pregnancy
Crown rump length, or CRL, measures the embryo from head to bottom. It is useful in the first trimester, when growth is fairly predictable. A careful CRL value can estimate gestational age in weeks and days. This page converts CRL into an age estimate, a due date, and comparison notes.
Why CRL Matters
Early dating affects many later decisions. It helps time screening tests. It also helps compare later fetal growth with the expected timeline. CRL is most helpful when the embryo is small enough for a clear straight measurement. Poor image angle, fetal flexion, or wrong caliper placement can change the result. For that reason, the calculator includes an uncertainty range.
What the Results Mean
The main result shows gestational age on the scan date. It also estimates the due date by counting forward to forty weeks. The fetal age line is about two weeks lower than gestational age, because pregnancy dating usually starts from the last menstrual period. If you enter an LMP or conception date, the tool compares those timelines with the CRL estimate.
Smart Use of the Calculator
Use one clean CRL value when possible. Choose millimeters or centimeters correctly. Enter the exact scan date. Add a small uncertainty value if the report gives a range, or if the measurement may be less certain. Review the chart to see where the point sits on the curve. Export the result when you need a record for review.
Important Limits
This calculator supports education and estimation. It does not diagnose pregnancy viability, fetal health, or abnormal growth. Dating rules can vary by clinic, country, and scan protocol. Multiple pregnancy, unusual anatomy, poor images, or assisted reproduction may require specialist judgment. Always confirm important decisions with a qualified healthcare professional.
When to Recheck
A repeat scan may be suggested when dates conflict, symptoms change, or image quality was limited. Small differences are common. Larger differences need context. The best interpretation comes from the full clinical picture, not one number alone. Keep the report, method, and scan date together for clear comparison. Use consistent records, because clear dating improves follow-up planning and patient communication safely.
FAQs
1. What is CRL?
CRL means crown rump length. It measures the embryo from the top of the head to the bottom. It is commonly used for early pregnancy dating.
2. Which CRL unit should I choose?
Choose the same unit used in your ultrasound report. If the report shows millimeters, choose millimeters. If it shows centimeters, choose centimeters.
3. Can this calculator replace a doctor?
No. It is an educational estimation tool. Ultrasound interpretation, pregnancy dating, and care decisions should be confirmed by a qualified healthcare professional.
4. Why does the calculator show fetal age?
Gestational age usually starts from the last menstrual period. Fetal age is about two weeks lower. It is included for helpful comparison only.
5. Why add CRL uncertainty?
Small measurement differences can shift the estimated age. The uncertainty field shows a possible range when image quality or caliper placement may vary.
6. What CRL range does this page support?
This calculator accepts CRL values from 1 mm to 95 mm. Values outside this range may need different clinical assessment or dating rules.
7. Why compare LMP with CRL?
LMP dating and ultrasound dating can differ. The comparison helps show how far the CRL estimate is from the menstrual timeline.
8. Can I save the result?
Yes. Use the CSV button for spreadsheet records. Use the PDF button for a simple printable report with key results.