Fundal Height Calculator
Calculate fundal height quickly with our gynecology & pregnancy tool. Get results based on evidence-based formulas with clear explanations.
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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.
Last reviewed: January 2026
Worked Examples
Example 1: Normal Fundal Height at 30 Weeks
Example 2: Small Fundal Height Requiring Follow-up
Background & Theory
The Fundal Height Calculator applies the following established principles and formulas. Health and medicine calculators are grounded in validated physiological measurement methods established through decades of clinical research. Body Mass Index, or BMI, is calculated by dividing weight in kilograms by height in meters squared (kg/m²), a formula originating from Adolphe Quetelet's 19th-century statistical work and later codified by the WHO into standard classifications: underweight below 18.5, normal weight 18.5 to 24.9, overweight 25 to 29.9, and obese at 30 and above. Basal Metabolic Rate quantifies the minimum energy required to sustain life at rest. The Mifflin-St Jeor equation, published in 1990 and widely regarded as the most accurate for most adults, calculates BMR as (10 × weight in kg) + (6.25 × height in cm) − (5 × age) ± sex adjustment. The older Harris-Benedict equations, revised in 1984 by Roza and Shizgal, remain in common use. Total Daily Energy Expenditure is derived by multiplying BMR by a physical activity factor ranging from 1.2 for sedentary individuals to 1.9 for extremely active ones, following the methodology validated by doubly labeled water studies. Body fat percentage can be estimated without laboratory equipment using the U.S. Navy circumference method, which uses neck, waist, and hip measurements, or via BMI-derived equations adjusted for age and sex. The Jackson-Pollock skinfold method offers higher precision with calipers. Blood pressure classification, according to the American College of Cardiology and the 2017 ACC/AHA guidelines, defines normal as below 120/80 mmHg, elevated as 120 to 129 systolic, and hypertension stage 1 as 130 to 139 systolic or 80 to 89 diastolic. Target heart rate zones for aerobic exercise are derived from maximum heart rate estimates, most commonly using the formula 220 minus age in years, with moderate-intensity training typically defined as 50 to 70 percent of maximum heart rate and vigorous intensity at 70 to 85 percent, consistent with CDC and American Heart Association guidelines. These thresholds guide safe and effective cardiovascular conditioning.
History
The history behind the Fundal Height Calculator traces back through the following developments. The history of health measurement stretches back to ancient Greece, where Hippocrates around 400 BCE laid the foundation for observational medicine by systematically recording patient symptoms, diet, and environment. His humoral theory, though scientifically superseded, established the principle that the body operates as an interconnected system subject to measurable imbalance. The transformation toward modern medicine accelerated in the 19th century. Louis Pasteur and Robert Koch developed germ theory in the 1860s and 1870s, identifying microorganisms as disease agents and enabling targeted interventions. Florence Nightingale, working during the Crimean War in the 1850s, introduced statistical analysis to nursing practice, demonstrating through data visualization that sanitation reduced mortality. Her work is foundational to evidence-based health measurement. The discovery of vitamins in the early 20th century, beginning with Casimir Funk's coinage of the term in 1912 and culminating in the isolation of vitamins A through K, created the field of nutritional science and gave rise to dietary reference intake frameworks. The World Health Organization, founded in 1948, subsequently established global standards for health metrics, disease classification through the International Classification of Diseases, and recommended daily allowances. The BMI as a clinical screening tool gained traction in the 1970s through Ancel Keys' large-scale epidemiological work, which validated Quetelet's index as a population-level obesity indicator. Through the 1980s and 1990s, the Framingham Heart Study produced landmark data linking cholesterol, blood pressure, and lifestyle factors to cardiovascular disease risk, directly shaping the numeric thresholds still used in health calculators. The evidence-based medicine movement, formalized by Gordon Guyatt and colleagues at McMaster University in the early 1990s, demanded that all health recommendations derive from systematically graded clinical evidence. The digital health era beginning in the 2000s brought these formulas to consumer devices, wearable sensors, and smartphone applications, expanding access to health self-monitoring on a global scale and enabling population-level data collection that continues to refine clinical reference ranges.
Frequently Asked Questions
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\nExpected fundal height: 30.4 cm\nNormal range: 28.4 to 32.4 cm (30.4 +/- 2)\nMeasured: 31 cm\nDifference: 31 - 30.4 = +0.6 cm\nHeight adjustment: (168 - 165) x 0.1 = +0.3 cm\nAdjusted 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\nNormal range: 32.0 to 36.0 cm\nMeasured: 30 cm\nDifference: 30 - 34 = -4.0 cm (below normal range)\nJohnson EFW: (30 - 12) x 155 = 2,790 g (6.1 lbs)\nHeight adjustment: (160 - 165) x 0.1 = -0.5 cm\nAdjusted 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.
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.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy