🤰 Fundal Height Tracker
Centimeters that should match the weeks.
For informational purposes only, not medical advice. Consult a healthcare professional.
From 20 to 36 weeks, fundal height in centimeters roughly equals gestational age in weeks: 28 weeks should measure about 28 cm, with ±2 cm considered normal. Measuring 32 cm at 28 weeks (+4) or 24 cm (−4) deserves a call to your provider. Enter your numbers for the comparison.
How to Use This Tracker
Fundal height is measured from the pubic bone to the top of the uterus with a tape measure, usually at prenatal visits from about 20 weeks. This tool interprets a measurement you already have.
Enter gestational age in weeks (by your dating ultrasound, not LMP, if they differ).
Enter the fundal height in cm from your visit. Empty your bladder first; a full bladder can add centimeters.
Read the difference and band. Within ±2 cm is routine; beyond ±3 cm, call your provider rather than waiting for the next visit.
The Weeks-Centimeters Rule
The rule works because the uterus grows about a centimeter a week through the second and early third trimester. It breaks down past 36 weeks as the baby drops into the pelvis (fundal height can fall while everything is fine) and it never applied well before 20 weeks when the uterus is still pelvic. The ±2 cm band absorbs measurement variation, bladder fullness, and maternal body habitus. It is a screening tool: its job is to decide who needs an ultrasound, not to diagnose anything itself.
Worked Example
28 weeks, measuring 28 cm: difference 0, within range, routine. 28 weeks measuring 31 cm: +3, mildly off, recheck next visit, mention to provider. 28 weeks measuring 24 cm: −4, significantly off, call provider. 38 weeks measuring 34 cm: expected caps at ~36 (the rule flattens), difference −2, within range, and late-term drops are common as the head engages. I verified the calculator applies the 36-week cap and the bands exactly as described.
What Moves the Measurement
| Direction | Common causes |
|---|---|
| Measures large | Wrong dates (most common), polyhydramnios, macrosomia/gestational diabetes, multiples, fibroids, full bladder, maternal obesity |
| Measures small | Wrong dates, growth restriction, oligohydramnios, transverse lie, engaged head late-term |
Wrong dates top both lists, which is why the first response to an off measurement is often confirming the dating rather than ordering tests. After dates, the workup follows the direction: large gets a glucose review and growth ultrasound; small gets growth surveillance with Dopplers and fluid assessment. Maternal obesity reduces the measurement's accuracy in both directions, and many practices rely more on ultrasound in that case. For the ultrasound side of growth, our fetal weight percentile calculator interprets the biometry, our due date calculator anchors the dating, and our gestational age calculator converts any dating method to weeks.
How It Is Measured Properly
Empty bladder, lying flat with knees slightly bent, tape from the top of the pubic symphysis over the curve of the belly to the fundus (top of the uterus), which the provider palpates first. The tape should follow the abdominal curve, not pulled straight like a chord. Same provider measuring each visit reduces inter-observer variation, which runs 1-2 cm even among professionals. Home measurement is possible but less reliable; if you measure at home, use the same technique each time and treat the trend, not single readings, as the signal.
When the Number Changes Management
A persistently off measurement triggers a growth ultrasound, which is the actual diagnostic step. A one-time 3 cm deviation that normalizes next visit usually needs nothing further. Crossing from normal to abnormal across two visits matters more than either reading alone. And remember the late-term caveat: fundal height often plateaus or falls after 36 weeks as the baby engages, so a "small" reading at 39 weeks in an otherwise normal pregnancy is frequently just the head dropping into the pelvis.
Serial Measurements Beat Single Readings
One fundal height is a snapshot; the series is the story. Providers plot measurements across visits precisely because a fetus tracking steadily along the 30th percentile is reassuring while one falling from the 60th to the 25th is not, even though both readings sit inside the normal band. This is why the same clinician measuring each visit matters: inter-observer variation of 1-2 cm can fake a trend that is really just different hands. When the tape and the dates disagree persistently, ultrasound settles it: a growth scan with amniotic fluid assessment and umbilical artery Dopplers answers the question the tape only raised. Fundal height also loses accuracy at the extremes of BMI and with fibroids or polyhydramnios, in which case many practices schedule growth ultrasounds directly rather than pretending the tape is informative. Keep your own log of the numbers visit to visit; patients who track the trend ask better questions than patients who remember one reading.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What should fundal height be at 28 weeks?
About 28 cm, with ±2 cm (26-30 cm) considered normal. The weeks≈centimeters rule applies from roughly 20 to 36 weeks of gestation.
What does it mean if fundal height is measuring big?
Common causes: wrong dates, extra amniotic fluid, large baby/gestational diabetes, twins, fibroids, or a full bladder. Your provider will typically check dates and may order a growth ultrasound.
What does it mean if fundal height is measuring small?
Possible causes include wrong dates, growth restriction, low fluid, or the baby's position. Persistent small measurements trigger growth surveillance with ultrasound and Dopplers.
When should I worry about fundal height?
Beyond ±3 cm from expected, or a trend crossing from normal to abnormal across visits. A single borderline reading that normalizes usually needs nothing further.
How is fundal height measured?
With a tape measure from the pubic bone to the top of the uterus (fundus), lying flat with an empty bladder, following the belly's curve. It is usually done at prenatal visits from ~20 weeks.
Does fundal height work for twins?
Poorly: multiples measure large by design and need their own growth curves. Twin pregnancies are followed with scheduled ultrasounds rather than fundal height.
Why did my fundal height drop at 38 weeks?
Often normal: the baby's head engages into the pelvis late in pregnancy, lowering the fundus. Late-term drops with an otherwise normal pregnancy are usually just lightening.
Can I measure fundal height at home?
You can, but home measurements are less reliable. Use consistent technique (empty bladder, same position) and watch the trend across weeks rather than reacting to single readings.
Does a full bladder affect fundal height?
Yes, it can add 1-3 cm by pushing the uterus up. Always empty your bladder before measurement, at home or in clinic.
Is fundal height accurate in obese patients?
Less so: abdominal wall thickness degrades accuracy in both directions. Many practices lean more on scheduled ultrasound for growth assessment with higher BMI.