Fundal Height Calculator
Calculate fundal height quickly with our gynecology & pregnancy tool. Get results based on evidence-based formulas with clear explanations.
Reviewed for accuracy by Rahul Singh, Health & Wellness Specialist
Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.
Fundal Height Calculator
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Formula: Expected Fundal Height (cm) = Gestational Age (weeks); EFW (g) = (FH - 12) x 155
Worked example — Assessment: Appropriate for gestational age | Difference: +0.6 cm | Within normal range
Formula
Expected Fundal Height (cm) = Gestational Age (weeks); EFW (g) = (FH - 12) x 155
After 20 weeks, fundal height in centimeters approximately equals gestational age in weeks, with a normal range of plus or minus 2 cm. The Johnson formula estimates fetal weight by subtracting 12 from the fundal height and multiplying by 155.
Worked Examples
Example 1: Normal Fundal Height at 30 Weeks
Problem:A woman at 30 weeks and 3 days gestation measures a fundal height of 31 cm. Her height is 168 cm. Is this within normal range?
Solution:Gestational age: 30 + 3/7 = 30.4 weeks Expected fundal height: 30.4 cm Normal range: 28.4 to 32.4 cm (30.4 +/- 2) Measured: 31 cm Difference: 31 - 30.4 = +0.6 cm Height adjustment: (168 - 165) x 0.1 = +0.3 cm Adjusted difference: 0.6 - 0.3 = +0.3 cm
Result:Assessment: Appropriate for gestational age | Difference: +0.6 cm | Within normal range
Example 2: Small Fundal Height Requiring Follow-up
Problem:A woman at 34 weeks gestation has a fundal height of 30 cm. Her height is 160 cm. Evaluate the measurement.
Solution:Expected fundal height: 34.0 cm Normal range: 32.0 to 36.0 cm Measured: 30 cm Difference: 30 - 34 = -4.0 cm (below normal range) Johnson EFW: (30 - 12) x 155 = 2,790 g (6.1 lbs) Height adjustment: (160 - 165) x 0.1 = -0.5 cm Adjusted difference: -4.0 - (-0.5) = -3.5 cm (still abnormal)
Result:Assessment: Small for gestational age | EFW: 2,790 g | Ultrasound recommended to rule out IUGR
Frequently Asked Questions
What is fundal height and how is it measured?
Fundal height is the distance measured in centimeters from the pubic bone (symphysis pubis) to the top of the uterus (uterine fundus). It is measured using a flexible tape measure with the pregnant woman lying supine with a partially empty bladder. The healthcare provider locates the top of the uterus by palpation and measures straight down to the top of the pubic bone. This measurement is typically taken at each prenatal visit after 20 weeks of gestation and recorded on a growth chart. Fundal height serves as a simple, non-invasive screening tool to monitor fetal growth and detect potential complications such as growth restriction or excessive growth.
How does fundal height correlate with gestational age?
After 20 weeks of pregnancy, fundal height in centimeters approximately equals the gestational age in weeks, give or take about 2 centimeters. This relationship, known as the McDonald rule, provides a quick clinical estimate of fetal growth. For example, at 28 weeks gestation the expected fundal height would be approximately 26 to 30 centimeters. Before 20 weeks, the uterus is still within the pelvis and fundal height measurements are less reliable. The correlation is strongest between 24 and 36 weeks, after which fetal engagement in the pelvis can cause the measurement to plateau or even decrease slightly. Individual variation exists due to maternal body habitus, fetal position, and amniotic fluid volume.
What does it mean if fundal height is larger than expected?
A fundal height measurement more than 2 centimeters above the expected value for gestational age may indicate several conditions requiring further evaluation. The most common causes include fetal macrosomia (a larger than average baby), polyhydramnios (excess amniotic fluid), multiple gestation (twins or more), or incorrect pregnancy dating. Maternal factors such as obesity, a full bladder during measurement, or uterine fibroids can also falsely elevate fundal height readings. When a large fundal height is detected, the typical next step is an ultrasound to assess fetal size, amniotic fluid volume, and confirm gestational dating. Gestational diabetes screening may also be recommended if not already completed, as uncontrolled blood sugar can lead to fetal overgrowth.
What does a smaller than expected fundal height indicate?
A fundal height measurement more than 2 centimeters below expected for gestational age raises concern for intrauterine growth restriction (IUGR), which means the fetus may not be growing at the expected rate. Other possible explanations include oligohydramnios (too little amniotic fluid), a transverse or oblique fetal lie, fetal engagement deep in the pelvis, or a slender maternal build. Incorrect gestational dating is also a common cause of apparent size discrepancy. When small fundal height is identified, ultrasound evaluation is performed to assess fetal biometry, estimated weight, amniotic fluid index, and placental function. Serial monitoring with Doppler studies of umbilical artery blood flow may be recommended if growth restriction is confirmed.
How accurate is fundal height measurement compared to ultrasound?
Fundal height measurement has a sensitivity of approximately 65 to 85 percent for detecting fetal growth abnormalities, making it a useful but imperfect screening tool. Ultrasound biometry provides significantly more accurate fetal weight estimates with an error margin of 10 to 15 percent, compared to fundal height which can vary by up to 3 centimeters between different examiners. Factors reducing fundal height accuracy include maternal obesity (which adds tissue between the tape and the uterus), multiple prior pregnancies (which alter abdominal wall tone), fibroids, and variations in measurement technique between providers. Despite these limitations, fundal height remains valuable as a low-cost, widely accessible screening method that can be performed at every prenatal visit. Abnormal fundal height findings should always be followed up with ultrasound for definitive assessment.
What is the Johnson formula for estimating fetal weight?
The Johnson formula is a clinical method for estimating fetal weight using fundal height measurements without ultrasound technology. The formula is: Estimated Fetal Weight in grams equals (Fundal Height in cm minus n) multiplied by 155, where n equals 12 if the presenting part is above the ischial spines or 11 if it is at or below the spines. For example, with a fundal height of 34 cm and the head above the spines: EFW = (34 - 12) x 155 = 3,410 grams (approximately 7.5 pounds). A modification adds 1 to n for each additional centimeter of fundal height when maternal weight exceeds 91 kg. While less precise than ultrasound estimates, the Johnson formula remains useful in resource-limited settings where ultrasound is unavailable.
How does maternal height and body type affect fundal height readings?
Maternal height and body composition significantly influence fundal height measurements and should be considered when interpreting results. Taller women with longer torsos tend to have slightly larger fundal height measurements because the uterus has more vertical space to expand, while shorter women may have smaller measurements even with appropriately sized babies. Maternal obesity can artificially increase fundal height due to the additional subcutaneous fat tissue between the measuring tape and the actual uterine fundus. Very muscular abdominal walls or a history of abdominal surgery with scarring may restrict uterine expansion and reduce fundal height. Some clinicians use customized fundal height charts that account for maternal height, weight, parity, and ethnicity to improve the accuracy of growth screening.
When should fundal height measurements begin during pregnancy?
Fundal height measurements typically begin at 20 weeks of gestation, when the uterine fundus reaches the level of the umbilicus and can be reliably measured externally. Before 20 weeks, the uterus remains within the bony pelvis and symphysis-fundal measurements are not clinically meaningful. From 20 weeks onward, the measurement is performed at each prenatal visit, usually every four weeks until 28 weeks, then every two weeks until 36 weeks, and weekly until delivery. This serial approach allows healthcare providers to track growth velocity over time, which is more informative than any single measurement. A pattern of consistently lagging or accelerating growth is more clinically significant than a single measurement that falls slightly outside the expected range.
Can fundal height predict the due date?
While fundal height correlates with gestational age, it should not be used as a primary method for establishing or changing an estimated due date. First-trimester ultrasound remains the gold standard for pregnancy dating, with accuracy within plus or minus five to seven days. Fundal height can provide a rough estimate of gestational age in settings where no ultrasound dating has been performed, but its accuracy for dating purposes is limited to plus or minus two to three weeks. Factors such as fetal size variation, amniotic fluid volume, maternal body habitus, and fetal position all introduce variability that makes precise dating impossible from fundal height alone. The primary clinical value of fundal height is in tracking growth trends over time rather than establishing specific gestational age.
What follow-up is recommended for abnormal fundal height measurements?
When fundal height falls outside the expected range by more than 2 centimeters, a systematic evaluation protocol is recommended. The first step is to verify the gestational age using the earliest available ultrasound dating. Next, a detailed ultrasound is performed to assess fetal biometry (head circumference, abdominal circumference, femur length), estimated fetal weight, amniotic fluid index, and placental location. If growth restriction is suspected, Doppler velocimetry of the umbilical artery helps evaluate placental function and fetal well-being. Serial ultrasound monitoring every two to four weeks tracks growth trajectory over time. Additional testing may include non-stress tests, biophysical profiles, and maternal blood work to evaluate for conditions such as preeclampsia or gestational diabetes that can affect fetal growth.
References
Reviewed for accuracy by Rahul Singh, Health & Wellness Specialist · Editorial policy
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