Explore an illustrative ±2 cm fundal-height band at 24–36 weeks in a well-dated singleton pregnancy, and compare a clinician measurement in cm or inches. This band is not a clinical reference interval.
Educational use only; not medical advice. This tool provides a rough screening estimate of an illustrative fundal-height band based on gestational age and should not be used to determine (date) gestational age. Fundal height should be measured and interpreted by a qualified prenatal care provider; ultrasound is used when accurate dating is needed.
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Fundal Height Formula
Fundal height, also called symphysis-fundal height (SFH), is the distance from the top of the pubic bone to the top of the uterus. In a well-dated singleton pregnancy, fundal height in centimeters often tracks closely with gestational age in weeks during mid-pregnancy. This calculator uses an illustrative ±2 cm band for education at 24–36 weeks. It is not a universal clinical reference interval, a diagnosis, or a way to establish pregnancy dating.
Variables
- FH = fundal height in centimeters
- GA = gestational age in weeks
- W = completed weeks
- D = additional days
How this calculator estimates fundal height
If gestational age is entered as weeks and days, it can be converted to a decimal week before calculating the expected range.
If you enter a measured value in inches, convert it to centimeters before comparing it with the expected range.
Example
At 28 weeks and 3 days, a measurement in that band matches this tool’s illustrative arithmetic; it does not establish normal fetal growth. A value a little above or below the estimate does not automatically mean there is a problem; the trend across visits matters more than one isolated number.
How to interpret the result
| Calculator result | Typical interpretation |
|---|---|
| Within the expected range | Inside this tool’s illustrative band. A prenatal clinician must interpret serial measurements using pregnancy dating and an appropriate growth chart; this alone does not establish normal growth. |
| Above the expected range | May reflect normal variation, incorrect dating, bladder fullness, fibroids, body habitus, fetal position, extra amniotic fluid, multiple gestation, or a larger-than-average baby. |
| Below the expected range | May reflect normal variation, incorrect dating, fetal descent later in pregnancy, maternal build, lower amniotic fluid, or a baby measuring smaller than expected. |
| Changing faster or slower than prior visits | A trend that changes unexpectedly is often more important than a single measurement and may lead to a recheck or ultrasound. |
When the week-equals-centimeter rule is most useful
Many prenatal care settings begin plotting serial SFH measurements around the mid-second trimester. The simple week-to-centimeter comparison is most useful in a fairly specific window.
| Pregnancy stage | Usefulness of fundal height |
|---|---|
| Before 24 weeks | Limited. The uterus is still relatively low in the pelvis, so fundal height does not correlate as reliably with gestational age. |
| About 24 to 36 weeks | This is the educational comparison window used here. Clinical guidelines recommend serial measurements after 24 weeks in singleton pregnancies, with growth-chart interpretation rather than this tool’s fixed band. |
| After about 36 weeks | Less reliable. The baby may descend into the pelvis, which can flatten or lower the measurement even when growth is normal. |
| Twins or higher-order multiples | This simple formula should not be used because uterine size does not follow the same pattern as a singleton pregnancy. |
How fundal height is measured clinically
- The patient is positioned comfortably, often semi-reclined.
- The clinician identifies the top of the pubic bone and the top of the uterine fundus.
- A tape measure is used to measure the distance between those points in centimeters.
- The number is compared with gestational age and with previous measurements on the growth record.
What can affect accuracy?
- Uncertain due date or incorrect pregnancy dating
- Different measurement technique between visits
- Bladder fullness
- Maternal body habitus or strong abdominal muscles
- Uterine fibroids
- Fetal position, including breech or transverse lie
- Low or high amniotic fluid volume
- Multiple gestation
- Late-pregnancy descent of the baby into the pelvis
Important limitations
- Fundal height is a screening tool, not a diagnosis.
- It should not be used by itself to establish the due date.
- A normal measurement does not guarantee normal growth, and an abnormal measurement does not prove a complication.
- Borderline results should be interpreted cautiously because acceptable variation can differ by technique, body type, and clinical setting.
- When measurements are repeatedly outside the expected range, clinicians often use ultrasound and the overall prenatal picture to evaluate growth and well-being.
When to follow up with a prenatal care provider
Discuss measurement concerns with your prenatal care provider. Contact maternity services promptly for reduced fetal movement, vaginal bleeding, leaking fluid, severe pain, or fever; do not wait for this calculator or a repeat measurement. This calculator is best used for education and rough screening, not for self-diagnosis or treatment decisions.
