Fundal Height Calculator - SFH Percentile and Fetal Weight

A fundal height calculator turns a single tape measurement into a pregnancy-growth snapshot, comparing the distance from your pubic bone to the top of your uterus against the expected range for the same week of pregnancy. Enter your gestational age in weeks and days, the symphysis-fundal height (SFH) you just measured, and your current weight, and the tool reports the expected median SFH, your INTERGROWTH-21st percentile band, a reverse estimate of gestational age from SFH, and a Johnson fetal weight estimate for the third trimester.

• • Quick pregnancy-growth check: Compare a tape measurement to the expected SFH for the same week so you can flag growth that is small or large for dates between prenatal visits.
• • Reverse gestational age estimate: Translate a single SFH into an approximate gestational age when your dating is uncertain.
• • Third-trimester fetal weight estimate: Use the Johnson formula with your measured SFH, weight, and presentation to estimate fetal weight in grams.

Fundal height is a low-cost, bedside screening tool recommended by the American College of Obstetricians and Gynecologists as the primary way to assess fetal growth at every in-person prenatal visit after 24 weeks. The calculator below uses the international INTERGROWTH-21st SFH standards so a measurement at a community clinic lines up with the same centile curve used in any research hospital.

If you only have an approximate last menstrual period, pair this tool with a pregnancy due date calculator to confirm dating before you trust the percentile band, because an off-by-one-week gestational age shifts the expected median SFH by about one centimeter.

The calculator runs the published INTERGROWTH-21st equation against your decimal gestational age, then looks up the 3rd, 10th, 50th, 90th, 95th, and 97th centile values to classify your measured SFH. If you are in the late third trimester, it also applies the Johnson formula to estimate fetal weight.

• GA: Exact gestational age in decimal weeks, computed from the weeks and days inputs (for example 28 weeks 4 days = 28.571).
• Median SFH: Expected symphysis-fundal height in centimeters for that gestational age, in the INTERGROWTH-21st international standard.
• ln(GA): Natural logarithm of the gestational age in weeks. The log term captures the flattening of the SFH curve past 36 weeks.
• Centile band: Comparison of the measured SFH against the 3rd, 10th, 90th, 95th, and 97th centile values from the INTERGROWTH-21st table.

When you provide a measured SFH, the calculator walks the centile table and returns the band your measurement falls into. Bands below the 10th or above the 90th centile are the same trigger most prenatal clinics use to recommend a growth ultrasound.

For gestational ages of 33 weeks and beyond the calculator also estimates fetal weight with Johnson's formula. Always confirm the estimated fetal weight against a formal growth scan before making delivery decisions.

According to BMJ / INTERGROWTH-21st Project (Papageorghiou et al., 2016), median symphysis-fundal height in centimeters equals 5.1333 + (0.1058 × GA²) − (0.02312 × GA²) × ln(GA) and the international 3rd to 97th centile standards are valid from 16 to 42 weeks of gestation.

Re-run the median SFH using a gestational age calculator whenever your dating is uncertain so the centile table lines up with the actual week of pregnancy.

Four ideas explain why a simple tape measurement is the workhorse of prenatal growth screening, and why the calculator uses the specific equations and centile tables it does.

These four ideas sit underneath every number the calculator prints. The SFH measurement is a physical landmark technique, the INTERGROWTH-21st standard is the reference population, the McDonald rule is the bedside shortcut, and the Johnson formula converts the SFH into a fetal weight when an ultrasound is not available.

Once the baby is born, the same percentile logic continues in the birthweight percentile calculator, which classifies actual birth weight against gestational age.

Run through these steps every time you take a measurement, and treat the result as a quick screen rather than a diagnosis.

1. 1 Confirm gestational age: Use the date of your last menstrual period or your earliest ultrasound dating. If the dates are uncertain, run a gestational age check first.
2. 2 Empty your bladder and lie down: A full bladder can add one to two centimeters to the fundal height, so empty it before measuring and lie on your back with knees slightly flexed.
3. 3 Measure from pubic bone to fundus: Place one end of a non-elastic tape on the top of the pubic symphysis and run it along the midline of the abdomen to the highest point of the fundus.
4. 4 Enter the values: Type the gestational age in weeks and any extra days, the measured SFH in centimeters, your current weight, and the fetal presentation.
5. 5 Read the percentile: Look at the centile band, the estimated fetal weight, and the reverse gestational age from SFH. If the band is below the 10th or above the 90th centile, share the result with your provider.
6. 6 Track across visits: Re-measure every two to four weeks and watch the trend. A steady drift away from the median is more concerning than a single off reading.

A 30-year-old at 30 weeks 2 days with a measured SFH of 28.5 cm and a weight of 68 kg will see a median SFH around 29.7 cm, a percentile band inside the 10th to 50th range, an SFH-derived gestational age near 29.6 weeks, and no Johnson fetal weight value (the formula needs at least 33 weeks).

Track the maternal side of the same visit with a pregnancy weight gain calculator, because a slow or fast weight trend often shows up in the fundal height trend first.

A quick SFH screen pays off in specific decisions a pregnant person and their care team make between formal ultrasounds.

• • Catches growth concerns earlier: Consistent SFH plotting identifies babies trending toward the 10th centile two to four weeks before a routine third-trimester scan, when targeted interventions have the most impact.
• • Doubles as a dating cross-check: The reverse gestational age from SFH gives a sanity check on your LMP-based dates, especially in the late second trimester when the McDonald rule works best.
• • Estimates fetal weight without an ultrasound: In rural or low-resource settings, the Johnson formula turns a single tape measurement into a usable fetal weight estimate, helpful for triage and referral decisions.
• • Standardizes what to ask your provider: Bringing a numeric percentile band to a prenatal visit makes the conversation concrete and helps you decide together whether a growth ultrasound is warranted.
• • Plots against a global standard: Using the INTERGROWTH-21st centile tables means the result is not anchored to a single clinic's historical patients, which reduces false alarms in healthy pregnancies.

Re-measure across visits to see the trend, and treat each result as a prompt for a question rather than a verdict.

A higher pre-pregnancy BMI tends to push the measured SFH below the median, so run your starting point through a BMI in pregnancy calculator to set the right baseline.

Several clinical factors can push a measured SFH above or below the median, and knowing which one applies helps you interpret the number.

• • The INTERGROWTH-21st SFH standard is validated from 16 to 42 weeks, so a measurement before 16 weeks should not be classified against the centile table.
• • Johnson's fetal weight formula was developed for term pregnancies in vertex presentation; accuracy drops for breech babies, multiples, and pregnancies complicated by diabetes or polyhydramnios. Treat the number as a rough estimate.
• • The SFH method is a screening tool, not a diagnostic one. An out-of-range centile band means an ultrasound is warranted, not that something is wrong.

If you have a higher BMI, expect a measurement one to two centimeters below the median and ask your provider to use a consistent technique across visits.

According to ACOG Clinical Consensus on Tailored Prenatal Care (2025), fundal height is the primary screening tool for assessing fetal growth at routine in-person prenatal visits after 24 weeks of gestation.

If the Johnson estimate here raises a flag, compare it with a formal ultrasound-based value from a fetal weight percentile calculator before any clinical decision is made.