Crown Rump Length (CRL) on Ultrasound: What It Means and CRL by Week (2026 Guide)

TL;DR

Crown rump length (CRL) is the measurement of your baby from the top of the head to the bottom (rump), taken on an early ultrasound, usually between 6 and 14 weeks. It is the most accurate way to date your pregnancy and estimate your due date in the first trimester (NHS) (Cleveland Clinic)。 It also helps confirm the baby's heartbeat (usually visible once CRL is about 7 mm) and is used in first-trimester screening like the NT scan (11 to 14 weeks). CRL grows steadily, from about 4 to 7 mm at 6 weeks to around 80 mm at 14 weeks. Small differences from "average" are normal. CRL does not tell the baby's gender. Always have your report explained by your doctor.

Quick Answer

Crown rump length (CRL) is the measurement of your baby from head to rump on an early ultrasound, taken between 6 and 14 weeks. It is the most accurate way to date your pregnancy and estimate your due date in the first trimester, and it helps confirm the heartbeat (usually visible around 7 mm CRL). CRL grows from about 4 to 7 mm at 6 weeks to around 80 mm at 14 weeks. It does not indicate gender.

Author: Mittali Khurrana, Senior Pregnancy Content Editor, Mylo Parenting Desk Medically reviewed by: Dr. Shruti Tanwar, MBBS, MS (Obstetrics & Gynecology), aligned with NHS, Mayo Clinic and FOGSI guidance Last updated: 29 June 2026

Medical Disclaimer: This article is for informational purposes only and is not a substitute for professional medical advice. CRL values are averages, and small differences are usually normal. Your doctor interprets your CRL along with your dates and full history. If you have any concern about your scan, ask your doctor.

Key Takeaways

• CRL is the baby's length from head to rump on an early ultrasound (Cleveland Clinic)
• It is measured between about 6 and 14 weeks
• It is the most accurate way to date a pregnancy in the first trimester (NHS)
• It helps confirm the heartbeat (usually visible once CRL is about 7 mm)
• It is used in first-trimester screening (like the NT scan at 11 to 14 weeks)
• CRL grows from about 4 to 7 mm at 6 weeks to around 80 mm at 14 weeks
• Small differences from average are normal
• CRL does NOT tell the baby's gender

What Is Crown Rump Length (CRL)?

Crown rump length (CRL) is the measurement of your developing baby from the top of the head (crown) to the bottom (rump), not including the legs or the yolk sac (NCBI/StatPearls)。

It is measured on an early ultrasound, usually between 6 and 14 weeks, when the baby is curled up and this length is the clearest, most reliable measurement to take.

CRL is one of the first and most useful measurements in early pregnancy, mainly because it dates the pregnancy very accurately.

Why Does CRL Matter?

CRL has several important uses in early pregnancy (NHS) (Cleveland Clinic):

Because early measurements are so reliable, your doctor may adjust your due date based on the CRL if it differs from your last-period calculation.

CRL by Week: Approximate Chart

These are approximate average CRL values by gestational age (NCBI/StatPearls):

Important: These are averages, and small differences are completely normal. Your exact CRL depends on your precise dates and the measurement. Do not compare your number to internet charts and worry, let your doctor interpret it (NHS)。

How Is CRL Measured?

CRL is measured during an ultrasound, often transvaginal in very early pregnancy for a clearer image (Cleveland Clinic):

1. The sonographer finds the clearest view of the baby lying in a neutral, slightly curled position
2. They measure the straight line from the crown (head) to the rump (bottom)
3. The legs and yolk sac are not included
4. The measurement is compared to standard charts to estimate gestational age

The scan is safe and uses no radiation (only sound waves).

What Affects CRL Measurements?

Several factors can cause small variations (NCBI/StatPearls):

A CRL that is a little different from the average is usually just a dating or measurement difference, not a problem.

What If the CRL Is Smaller or Larger Than Expected?

Small differences are usually normal and simply reflect your exact dates (NHS):

• A smaller CRL often means you are earlier in pregnancy than calculated (especially with irregular periods)
• A larger CRL may mean you are further along than thought
• Your doctor may adjust your due date accordingly
• In some cases, a follow-up scan is arranged to confirm growth and the heartbeat

A single measurement is interpreted together with your history and, if needed, a repeat scan, not in isolation. If you have any concern, your doctor will explain and guide you.

➡️ Related read: What to expect in your 7-week pregnancy scan report

Does CRL Tell the Baby's Gender?

No. CRL is a length measurement used for dating, not for determining gender (NCBI/StatPearls)。 The baby's external genitals are not developed enough to determine sex this early, and CRL cannot predict it.

In India, sex determination is illegal under the PCPNDT Act. Scans, including CRL, are done for health monitoring only.

Indian Context: What Indian Mothers Should Know

1. Accurate dating helps: The CRL at your first scan is the most reliable way to date your pregnancy, especially with irregular periods (FOGSI)
2. Do not self-interpret: Avoid matching your CRL to internet charts and worrying, let your gynaecologist explain it
3. No gender from CRL: Sex determination is illegal in India (PCPNDT Act); CRL cannot and should not be used for this
4. NT scan timing: The 11 to 14 week NT (nuchal translucency) scan uses CRL to time the screening correctly
5. Cost: An early dating scan in India typically costs about ₹800 to ₹2,500
6. Keep your scans: Bring previous reports to each visit so your doctor can track growth

Myths vs Facts About CRL

FAQs: Crown Rump Length (CRL)

What is crown rump length (CRL) in pregnancy?

CRL is the measurement of your baby from the top of the head to the bottom (rump) on an early ultrasound, taken between about 6 and 14 weeks (NCBI/StatPearls)。 It is the most accurate way to date a pregnancy and estimate the due date in the first trimester.

CRL kya hota hai aur kyun important hai? (Hinglish)

CRL (crown rump length) aapke baby ki head se rump tak ki length hai, jo early ultrasound (6 se 14 hafte) mein maapi jati hai. Yeh first trimester mein pregnancy date aur due date estimate karne ka sabse accurate tarika hai. Yeh heartbeat confirm karne (lagbhag 7 mm CRL par) aur NT scan timing ke liye bhi use hoti hai. CRL se gender nahi pata chalta.

How is CRL used to estimate the due date?

CRL is compared to standard growth charts to estimate the gestational age, and from that, your due date (NHS)。 An early CRL is often accurate to within a few days, so your doctor may adjust your due date based on it.

What is a normal CRL at each week?

Approximate averages: about 4 to 7 mm at 6 weeks, 23 mm at 9 weeks, 53 mm at 12 weeks, and 80 mm at 14 weeks (NCBI/StatPearls)。 These are averages, and small differences are normal. Your doctor interprets your exact value.

Meri CRL chart se thodi alag hai, chinta ki baat hai? (Hinglish)

Aksar nahi. CRL ke values average hote hain, aur thoda alag hona bilkul normal hai. Chhoti CRL ka matlab aksar yeh hota hai ki aap soche se kam hafte mein hain (khaas kar irregular periods mein). Internet chart se compare karke tension na lein, apne doctor se report samjhein. Koi chinta ho toh doctor guide karenge.

Does CRL tell the gender of the baby?

No. CRL is a length measurement for dating, not a gender test (NCBI/StatPearls)。 The genitals are not developed enough to determine sex this early. In India, gender determination is also illegal under the PCPNDT Act.

When is the heartbeat seen in relation to CRL?

A fetal heartbeat is usually visible once the CRL reaches about 7 mm (around 6 to 7 weeks) (Cleveland Clinic)。 If the CRL is smaller than this, the heartbeat may simply not be visible yet, and a repeat scan may be advised.

Why might my doctor change my due date after the CRL scan?

Because the early CRL is more accurate than the last-period date for dating (NHS)。 If the CRL suggests you are slightly earlier or later than your last-period calculation, your doctor adjusts your due date to the more accurate estimate.

References

1. NCBI / StatPearls. "Crown Rump Length." https://www.ncbi.nlm.nih.gov/books/NBK470596/
2. NHS UK. "Ultrasound Scans in Pregnancy." https://www.nhs.uk/pregnancy/your-pregnancy-care/ultrasound-scans/
3. Cleveland Clinic. "Ultrasound (Fetal Imaging)." https://my.clevelandclinic.org/health/diagnostics/4995-ultrasound-fetal-imaging
4. Mayo Clinic. "Fetal Ultrasound." https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/fetal-ultrasound/art-20047994
5. FOGSI (Federation of Obstetric and Gynaecological Societies of India). https://www.fogsi.org/