Crown-rump Length Calculator
Calculate gestational age and due date from CRL ultrasound measurements
Calculate Gestational Age from CRL
Distance from crown of head to rump (buttocks)
Optimal: 5-85 mm (7-16 weeks)
Most accurate: 9-14 weeks of pregnancy
CRL in mm = 0.0 mm
🏥 Important Medical Disclaimer
• This calculator provides estimates based on the Robinson & Fleming equation
• CRL dating is most accurate between 9-14 weeks of pregnancy
• Always compare with last menstrual period (LMP) date
• Ultrasound measurements should be performed by qualified professionals
• This tool cannot replace professional medical assessment
• Consult your healthcare provider for pregnancy monitoring and care
Example Calculation
CRL Measurement: 55 mm
Calculation: GA = 8.052 × √(55 × 1.037) + 23.73
Step 1: 55 × 1.037 = 57.035
Step 2: √57.035 = 7.552
Step 3: 8.052 × 7.552 = 60.81
Step 4: 60.81 + 23.73 = 84.54 days
Result: 84 days = 12 weeks 0 days
Crown-rump Length Chart
| CRL (mm) | Gestational Age | CRL (mm) | Gestational Age |
|---|---|---|---|
| 5 | 6+0 | 50 | 11+5 |
| 10 | 7+1 | 55 | 12+1 |
| 15 | 7+6 | 60 | 12+3 |
| 20 | 8+4 | 65 | 12+6 |
| 25 | 9+2 | 70 | 13+1 |
| 30 | 9+6 | 75 | 13+4 |
| 35 | 10+2 | 80 | 13+6 |
| 40 | 10+6 | 85 | 14+1 |
| 45 | 11+2 |
Based on Robinson & Fleming equation. Format: weeks+days
About CRL Measurement
What is CRL?
Crown-rump length
Distance from head to buttocks
Best Timing
9-14 weeks pregnancy
Most accurate dating period
Accuracy
±3-5 days typically
Most precise early dating method
Key Points
Most accurate dating method in first trimester
Reliable between 7-16 weeks gestation
Should be measured by qualified sonographer
Compare with LMP date for accuracy
After 14 weeks, use fetal biometry instead
Understanding Crown-rump Length
What is Crown-rump Length?
Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump). It is the most accurate parameter for dating pregnancies in the first trimester.
When is CRL Used?
- •Between 7-16 weeks of pregnancy
- •Most accurate between 9-14 weeks
- •When LMP date is uncertain
- •For dating IVF pregnancies
Robinson & Fleming Formula
GA = 8.052 × √(CRL × 1.037) + 23.73
- GA: Gestational age in days
- CRL: Crown-rump length in millimeters
- 1.037: Correction factor
- 8.052, 23.73: Regression coefficients
Note: This equation is ranked among the 4 most accurate fetal assessment equations by the INTERGROWTH-21st Project.
Accuracy by Gestational Age
Clinical Applications
- •Confirm gestational age
- •Estimate due date
- •Assess fetal viability
- •Plan prenatal care schedule
- •Screen for chromosomal abnormalities
⚠️ Important Considerations
- •CRL should be measured in a sagittal plane with the fetus in neutral position
- •Measurement should exclude the limbs and yolk sac
- •Multiple measurements should be taken and the largest used
- •After 14 weeks, fetal biometry (BPD, HC, AC, FL) is more accurate