Enter the gestational age of the pregnancy into the calculator to estimate the expected fundal height. Fundal height is a measure of the size of the uterus used to assess fetal growth and development during pregnancy. Clinically, fundal height (in cm) is most commonly compared to gestational age (in weeks) as a rule of thumb in mid-pregnancy (roughly 20–36 weeks).
Educational use only; not medical advice. This tool provides a rough screening estimate of expected fundal height 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 that rule of thumb to estimate an expected screening range, not an exact diagnosis.
FH_{expected} \approx GAFH_{range} \approx GA \pm 2 \text{ cm}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.
GA = W + \frac{D}{7}FH_{min} = GA - 2 \qquad FH_{max} = GA + 2If you enter a measured value in inches, convert it to centimeters before comparing it with the expected range.
FH_{cm} = FH_{in} \times 2.54Example
GA = 28 + \frac{3}{7} \approx 28.4FH_{range} \approx 28.4 \pm 2 = 26.4 \text{ to } 30.4 \text{ cm}At 28 weeks and 3 days, a fundal height in roughly that range would usually be considered consistent with the screening estimate. 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 | Usually reassuring as a screening value when pregnancy dating is known and measurements are tracking normally over time. |
| 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 about 20 weeks | Limited. The uterus is still relatively low in the pelvis, so fundal height does not correlate as reliably with gestational age. |
| About 20 to 36 weeks | Most useful for routine screening in a singleton pregnancy. This is the main range the calculator is designed around. |
| 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
Contact your prenatal care provider if the measurement is repeatedly outside the expected range, your abdominal size changes noticeably between visits, or you have symptoms such as vaginal bleeding, leaking fluid, severe pain, fever, or reduced fetal movement. This calculator is best used for education and rough screening, not for self-diagnosis or treatment decisions.
