health

Fundal Height Calculator

Fundal height—the distance from the pubic symphysis to the top of the uterus—serves as a practical clinical marker for fetal growth and gestational age estimation. Midwives and obstetricians routinely use this measurement to screen for growth abnormalities and complications. This calculator bridges clinical assessment and patient understanding, converting between gestational age, measured fundal height, and estimated fetal weight using evidence-based formulas.

Last updated: April 19, 2026

Creators Małgorzata Koperska, MD

Reviewers Łucja Zaborowska and Adena Benn

7,123 people find this calculator helpful

What Is Fundal Height?

Fundal height represents the vertical distance from the uppermost point of the pregnant uterus (the fundus) to the pubic symphysis. Clinicians measure this with a standard tape measure placed along the maternal abdomen, typically starting measurement around 12–14 weeks gestation when the fundus becomes palpable above the pubic bone.

The measurement serves two purposes: it confirms that fetal development is tracking appropriately for gestational age, and it flags potential complications such as intrauterine growth restriction, polyhydramnios, or multiple pregnancies. A fundal height that is significantly smaller or larger than expected warrants further investigation via ultrasound.

Physical landmarks help orient measurement:

At 20–22 weeks, the fundus typically reaches the level of the umbilicus
By 36 weeks, the fundus reaches its highest point near the xiphoid process
After 36 weeks, the fundus may descend slightly as the fetus engages in the pelvis (lightening)

Calculating Median Fundal Height from Gestational Age

When a direct measurement is unavailable or for clinical comparison, the median expected fundal height can be derived from gestational age. The relationship between gestational age and fundal height follows a non-linear curve that accelerates in the second trimester and plateaus near term.

Median SFH (cm) = 5.1333 + (0.1058 × GA²) − (0.02312 × GA²) × ln(GA)

SD SFH (cm) = 0.9923 + (0.0258 × GA)

GA (weeks) = weeks + (days ÷ 7)

SFH — Symphysis-fundal height in centimeters
GA — Gestational age in completed weeks plus fractional days
SD — Standard deviation of fundal height; normal range spans roughly ±2 SD from median

Determining Gestational Age from Fundal Height

In settings where ultrasound dating is unavailable or when confirmatory assessment is needed, the inverse calculation—estimating gestational age from measured fundal height—can be applied using Johnson's formula. This approach is most reliable between 16 and 40 weeks, as earlier measurements are too small for precise dating and later measurements approach a plateau.

The formula performs best when:

The mother's BMI is within typical range (measurement becomes less reliable in obese or very thin patients)
Single pregnancy (multiple gestations alter the fundal height–age relationship)
No polyhydramnios or other fluid abnormalities are present
Measurement is taken by a trained clinician using consistent technique

Discrepancies between ultrasound dating and fundal-height-derived age warrant further imaging to exclude growth restriction, dating error, or pregnancy complications.

Estimating Fetal Weight via Fundal Height

Johnson's formula provides a simple bedside estimate of fetal weight based on fundal height, maternal weight, and fetal position. This method is most accurate after 33–36 weeks when the fetus is in vertex presentation (head-down position, as confirmed by clinical examination or ultrasound).

The formula is:

Fetal weight (g) = (SFH − maternal weight − vertex position constant) × 155

Several caveats apply:

Accuracy is limited compared to ultrasound biometry, with typical errors of ±10–15% in lean mothers but wider margins in obese pregnancies
Non-vertex positions (transverse, oblique) invalidate the formula
The formula does not account for individual variation in maternal habitus or amniotic fluid volume
Serial measurements trending over weeks are more informative than a single estimate

Modern practice typically reserves this method for quick clinical screening when ultrasound is temporarily unavailable, rather than relying on it for definitive growth assessment.

Practical Tips for Accurate Fundal Height Measurement

Measurement technique and interpretation require care to avoid misclassification of growth abnormalities.

Standardize measurement position and technique — Always measure with the mother supine or semi-recumbent, bladder emptied, and tape measure placed vertically from the superior border of the pubic symphysis to the top of the uterine fundus. Inconsistent technique—such as measuring at an angle or with a full bladder—introduces variability that can mimic pathology.
Account for maternal factors that affect accuracy — Maternal obesity, lax abdominal wall musculature, amniotic fluid volume, and anterior placental location all influence fundal height independent of fetal size. A fundus that feels smaller than expected may indicate a posteriorly implanted placenta or suboptimal measurement rather than true growth restriction.
Use serial measurements rather than isolated values — A single measurement outside the expected range prompts concern, but a series of measurements tracking roughly parallel to the expected curve is reassuring. Growth velocity—how much fundal height increases over 2–4 weeks—is often more informative than absolute values.
Combine fundal height with other clinical indicators — Fundal height screening is most useful as part of a broader assessment that includes uterine tenderness, amniotic fluid palpation, fetal movement history, and blood pressure trends. Alone, it cannot diagnose complications and should prompt confirmatory ultrasound when abnormalities are suspected.

Frequently Asked Questions

What is the normal fundal height at different stages of pregnancy?

Fundal height follows a predictable arc: at 12–14 weeks, the fundus is just palpable above the pubic bone; at 20–22 weeks, it reaches the level of the umbilicus; by 36 weeks, it reaches near the xiphoid process or costal margin. After 36 weeks, the fundus may descend 1–2 cm as the fetus engages in the pelvis. However, these landmarks are population averages; individual variation is normal. The formula SFH = 5.1333 + (0.1058 × GA²) − (0.02312 × GA²) × ln(GA) gives a more precise estimate for any given gestational age.

When should I start having my fundal height measured?

Measurement typically begins at the 12–14 week appointment when the fundus becomes easily palpable above the pubic bone. Before this, the uterus remains largely pelvic and is difficult to measure reliably. In early pregnancy, dating via first-trimester ultrasound is preferred for accuracy. Once measurement begins, it should continue at each prenatal visit—roughly every 2–4 weeks in the second trimester and every 1–2 weeks in the third trimester—to track the growth trajectory.

Can fundal height accurately predict my baby's birth weight?

Fundal height can provide a rough estimate of birth weight using Johnson's formula, but accuracy is modest—typically ±10–15% in non-obese mothers and wider in overweight pregnancies. The formula is most reliable after 33–36 weeks in vertex presentation. However, ultrasound biometry remains the gold standard for fetal weight estimation. Fundal height is best used as a screening tool to flag babies who are notably smaller or larger than expected, prompting further evaluation rather than serving as the sole basis for clinical decisions about delivery timing or intervention.

What does it mean if my fundal height is larger or smaller than expected?

Fundal height that exceeds the expected range may indicate polyhydramnios (excessive amniotic fluid), multiple pregnancy, maternal obesity, or miscalculated gestational age—not necessarily a larger baby. Fundal height below the expected range can suggest intrauterine growth restriction, oligohydramnios (low fluid), dating error, or maternal factors like a lax abdominal wall. Discrepancies warrant further evaluation, typically with ultrasound, to assess fetal biometry, amniotic fluid volume, and placental function. Serial measurements trending normally are more reassuring than a single outlier.

Is fundal height measurement reliable in overweight or obese pregnancies?

Fundal height measurement becomes progressively less reliable as maternal BMI increases. Increased abdominal fat and altered body composition make it harder to consistently identify the fundal border, and the relationship between fundal height and fetal size shifts. Clinicians may apply empirical adjustments, but these are imperfect. In overweight and obese pregnancies, ultrasound-based fetal biometry is preferred over fundal height for growth assessment. However, fundal height surveillance remains part of routine care and can still flag gross abnormalities or significant changes from baseline.

How is gestational age estimated from fundal height if ultrasound dating is unavailable?

Johnson's formula—GA (weeks) = 6.5858 − 2.7073 × √SFH + 1.2952 × SFH—allows estimation of gestational age from measured fundal height. This inverse calculation is most reliable between 16 and 40 weeks and works best with singleton, vertex-presenting pregnancies and mothers of typical BMI. Dating errors of ±2–3 weeks are common, particularly near term when the fundal-height curve plateaus. In clinical practice, this method serves as a backup when ultrasound is not available, but first-trimester ultrasound remains the gold standard for dating accuracy.

More health calculators (see all)

Alcohol Units Calculator Fiber Calculator Paracetamol Dosage Calculator Vitamin Calculator Mean Sac Diameter Calculator SCORAD Calculator Dead Space Calculator Estimated Average Glucose Calculator