Online Ultrasound gestation age calculator

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Use our free Online ultrasound gestation age calculator to determine the duration of pregnancy by ultrasound results. You can use it to measure embryo length and determine the gestational age accurately. with great accuracy

It is very important to know the duration of your pregnancy so that you can determine the duration of your labor and to monitor the development of the fetus and determine the duration of your maternity leave.

ultrasound gestation age calculator.


Embryo length, mm
Please, Enter all values correctly.
Pregnancy term
weeks days

How accurate is an ultrasound for gestational age?

The baby can be measured after the last menstrual period of the mother as early as 5 or 6 weeks. Measuring the baby with ultrasound in early pregnancy is most reliable. Later in pregnancy, it becomes less accurate. Between the 8th and 18th weeks of pregnancy, the best time to predict gestational age using ultrasound.

The most reliable way to determine gestational age is to use the first day of the last menstrual period of the female and verify this gestational age with the ultrasound test calculation.

Does ultrasound measure gestational age or fetal age?

According to The American College of Obstetricians and Gynecologists, you can use these methods for estimating gestational age and due date:

  • Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age.
  • If a pregnancy resulted from assisted reproductive technology (ART), the ART-derived gestational age should be used to assign the estimated due date (EDD). For instance, the EDD for a pregnancy that resulted from in vitro fertilization should be assigned using the age of the embryo and the date of transfer.
  • A pregnancy without an ultrasound examination that confirms or revises the EDD before 22 0/7 weeks of gestational age should be considered suboptimally dated.(source)

How is gestation calculated?

  • Gestation by LMP is calculated from the first day of the last menstrual period.
  • Gestation by CRL is calculated: Weeks = 5.2876 + (0.1584 * Crown_Rump_Length) – (0.0007 * Crown_Rump_Length2). This will be gestation at time of ultrasound.
  • Gestation by BPD is calculated using the formula: Days = 2 * BPD + 44.2. This will be gestation at the time of the ultrasound.
  • Gestation by HC is calculated: Weeks = eTo(1.854 + (0.010451 * Head_Circumference) – (0.000029919 * Head_Circumference2) + 0.000000043156 * Head_Circumference3). This will be gestation at time of ultrasound.

What’s the difference between gestational age and fetal age?

Gestational age is the age of the pregnancy from the last normal menstrual period (LMP), and fetal age is the actual age of the growing baby.

Most references to pregnancy are usually in gestational age rather than fetal age development, but we’ve included both, so it’s obvious what the stage development is. Measurements will be given from head to toe in total length, but each pregnancy vary in measurements of weight and length, and these are just a general guideline.

Additionally, pregnancy is split into trimesters lasting between 12 and 14 weeks each. These can be measured from different dates, similar to development, so not all trimester calculations will be identical. The following information splits the three trimesters into slightly more than 3 months each.

The first trimester is week 1 through the end of week 13, consisting of the first, second and third months. Usually, the second trimester ends around the 26th week and consists of the completed fourth, fifth and sixth months. The third-trimester end between the 38th – 42nd week and is the 7th, 8th and 9th month makes a complete pregnancy.


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