Crown-Rump Length Calculator
Estimate gestational age, due date, and conception date using your CRL measurement.
Wondering about your baby’s growth during the first trimester? Our Crown-Rump Length Calculator helps you understand your baby’s early development by measuring the distance from the top of the head (crown) to the bottom of the buttocks (rump). This critical measurement, taken during early ultrasound scans, provides accurate gestational dating and ensures your baby is growing appropriately in these crucial early weeks. Discover how this precise measurement helps monitor your pregnancy’s healthy progression from the very beginning.
Start by calculating your estimated due date with our Due Date Calculator.
How to Use the Crown-Rump Length Calculator
Our calculator helps interpret early ultrasound measurements in three simple steps:
Enter Your Ultrasound Findings:
CRL Measurement: Input the crown-rump length in millimeters
Gestational Age: Enter the estimated age based on CRL
Scan Date: Note when the ultrasound was performed
Ultrasound Type: Transvaginal or abdominal scan
Provide Additional Pregnancy Details:
Last Menstrual Period (LMP): First day of your last period
Cycle Length: Your typical menstrual cycle duration
Previous Pregnancies: Any relevant reproductive history
Current Symptoms: Pregnancy symptoms you’re experiencing
Get Your Personalized Analysis:
View your accurate gestational age based on CRL
See your adjusted due date if different from LMP calculation
Receive growth percentile compared to expected ranges
Get follow-up recommendations for your next scan
For optimal tracking, maintain a pregnancy journal with all your ultrasound results.
Understanding Crown-Rump Length Measurements
CRL is the most accurate method for dating early pregnancies:
CRL to Gestational Age Conversion:
CRL Measurement (mm) Gestational Age (Weeks + Days) Key Developmental Milestones
5 mm 6 weeks + 0 days Heartbeat begins detectable
10 mm 7 weeks + 0 days Major organ formation starts
20 mm 8 weeks + 2 days Limb buds developing
30 mm 9 weeks + 3 days Clearly recognizable as human
40 mm 10 weeks + 2 days Rapid brain development
50 mm 11 weeks + 1 days Vital organs functioning
60 mm 12 weeks + 0 days Risk of miscarriage decreases
Accuracy of CRL Dating:
±3-5 days accuracy in first trimester
Most precise between 7-12 weeks
Becomes less accurate after 13 weeks
Gold standard for pregnancy dating
Track your pregnancy progression with our Pregnancy Calculator.
Why Crown-Rump Length Matters in Early Pregnancy
This measurement provides crucial information for your pregnancy care:
Accurate Pregnancy Dating:
Confirms gestational age more precisely than LMP
Establishes reliable due date for planning
Identifies possible discrepancies with LMP-based dating
Guides timing for future tests and screenings
Early Development Assessment:
Verifies appropriate growth for gestational age
Detects potential issues early in pregnancy
Provides reassurance of normal development
Helps identify multiples in early stages
Clinical Decision Making:
Determines viability through appropriate growth
Guides management of early pregnancy concerns
Helps plan appropriate prenatal testing schedule
Provides baseline for future growth assessments
Monitor your overall pregnancy health with our Pregnancy Health Calculator.
When and How CRL is Measured
Understanding the timing and procedure:
Optimal Measurement Period:
6-13 weeks gestation for maximum accuracy
Best visualized via transvaginal ultrasound early on
Abdominal ultrasound may be used after 8-9 weeks
Routine dating scan typically between 8-12 weeks
Proper Measurement Technique:
Baby in neutral position without flexion or extension
Maximum straight-line length from crown to rump
Multiple measurements taken for accuracy
Average used for final determination
What Technicians Look For:
Clear endpoints for accurate measurement
Appropriate curvature for gestational age
Consistent growth compared to previous scans
Overall fetal morphology and development
Calculate your conception date with our Conception Date Calculator.
Interpreting Your CRL Results
Understanding what the measurements mean for your pregnancy:
Normal Growth Patterns:
Approximately 1 mm per day growth in early pregnancy
Consistent increase expected between scans
Slight variations normal based on genetics
Percentile rankings indicate relative size
Potential Concerns:
Small for gestational age may need monitoring
Large for gestational age may indicate dating error
No growth between scans requires investigation
Extreme discrepancies may suggest underlying issues
Follow-up Actions:
Repeat scanning if measurements unclear
Additional testing if concerns arise
Close monitoring for at-risk pregnancies
Specialist referral if abnormalities suspected
Use pregnancy tracking apps to monitor your progress.
Factors Affecting CRL Measurements
Variables that can influence accuracy and interpretation:
Technical Factors:
Ultrasound machine quality and resolution
Technician experience and skill level
Fetal position during measurement
Measurement technique consistency
Biological Variations:
Genetic factors influencing early growth
Maternal health conditions affecting development
Multiple pregnancies with individual variations
Normal biological diversity in growth patterns
Measurement Timing:
Gestational age at time of measurement
Time of day potentially affecting fetal position
Maternal hydration status possibly influencing clarity
Interval between scans for growth assessment
Track your symptoms with our Pregnancy Symptom Tracker.
CRL vs. Other Dating Methods
Comparing early pregnancy assessment techniques:
Comparison of Dating Methods:
Method Accuracy Best Timeframe Advantages Limitations
CRL ±3-5 days 6-13 weeks Most accurate early dating Less reliable after 13 weeks
LMP ±1-2 weeks First trimester Simple, non-invasive Requires regular cycles
hCG Levels ±1 week 4-7 weeks Early confirmation Wide normal ranges
Fundal Height ±2-3 weeks Second trimester Clinical assessment Affected by multiple factors
Why CRL is Preferred:
Direct measurement of fetal size
Not dependent on maternal recall
Visual confirmation of viability
Early detection of potential issues
Complementary Methods:
Combining CRL with LMP for best dating
Using hCG trends for very early pregnancy
Following with anatomy scan at 20 weeks
Clinical correlation with symptoms and signs
Calculate your pregnancy weight gain with our Pregnancy Weight Gain Calculator.
Common CRL Questions Answered
Addressing frequent concerns and misconceptions:
Q: What if my CRL measurement doesn’t match my LMP date?
A: CRL is more accurate. Providers typically adjust the due date based on CRL if there’s more than 5-7 days difference from LMP dating.
Q: Can CRL predict the gender of the baby?
A: No, CRL measures size and developmental progress, not gender. Gender determination typically occurs around 16-20 weeks.
Q: What does it mean if my baby measures small on CRL?
A: It could indicate incorrect dating, slow growth, or a genetic variation. Your provider will monitor closely and may recommend follow-up scans.
Q: How often should CRL be measured?
A: Typically once during the dating scan (8-12 weeks). Repeated measurements are only needed if there are concerns about growth or dating.
Q: Can CRL detect abnormalities?
A: While primarily for dating, abnormal CRL measurements or morphology may prompt further investigation for potential issues.
Special Considerations in CRL Interpretation
Unique situations requiring specific attention:
Multiple Pregnancies:
Individual measurements for each fetus
Comparing growth between multiples
Earlier detection of growth discrepancies
Close monitoring for twin-twin issues
IVF Pregnancies:
Known conception date provides reference
Comparing CRL to expected based on transfer date
Validation of precise dating in ART pregnancies
Earlier reassurance of appropriate development
High-Risk Situations:
Maternal health conditions affecting growth
Previous pregnancy complications
Advanced maternal age considerations
Family history of genetic conditions
Use fetal Doppler devices for between-appointment reassurance (with medical guidance).
Next Steps After Your Dating Scan
After receiving your CRL measurements:
Immediate Actions:
Discuss results with your healthcare provider
Update your due date if adjusted
Schedule next appointments based on new timeline
Begin prenatal vitamins if not already started
Planning and Preparation:
Adjust work leave dates if due date changed
Update pregnancy apps with accurate information
Begin researching prenatal testing options
Start planning for upcoming trimesters
Health Management:
Follow provider recommendations for follow-up
Maintain healthy habits supporting fetal growth
Attend all scheduled prenatal appointments
Monitor symptoms and report concerns promptly
Consider pregnancy journals to document your journey.
Understanding Percentiles and Growth Charts
Interpreting where your baby measures compared to averages:
Percentile Explanations:
50th percentile: Average size for gestational age
Below 10th percentile: May require monitoring
Above 90th percentile: May indicate dating error or genetics
Consistent percentile: More important than single measurement
Growth Velocity:
Appropriate growth between scans is crucial
Crossing percentiles may warrant investigation
Consistent pattern typically indicates normal variation
Sudden changes require medical assessment
Genetic Influences:
Parental size affects baby’s measurements
Ethnic variations in growth patterns
Family growth patterns may be relevant
Discuss with provider if concerns about size
Track your nutrition with our Pregnancy Nutrition Calculator.
When to Seek Additional Evaluation
Red flags that warrant further investigation:
Concerning Findings:
No growth over 7-10 day period
Extreme discrepancies (>2 weeks difference from dates)
Abnormal morphology noted during scan
No heartbeat when expected for CRL size
Maternal Symptoms Warranting Attention:
Heavy bleeding with pain
Severe abdominal pain
Sudden disappearance of pregnancy symptoms
Previous miscarriage history with current concerns
Follow-up Protocols:
Repeat ultrasound in 1-2 weeks if uncertain
hCG trend monitoring for very early pregnancies
Specialist referral for high-risk situations
Genetic counseling if abnormalities suspected
Use medical documentation organizers to keep track of test results.
Next Steps in Your Pregnancy Journey
Now that you have your accurate dating:
Celebrate this milestone in your pregnancy journey
Share the news with family and friends if ready
Begin planning for the coming months
Focus on healthy habits supporting baby’s growth
Enjoy this special time as your pregnancy progresses
Continue tracking your pregnancy with our Weekly Pregnancy Calculator.
