Fundal Height Calculator
Use this fundal height calculator to check whether your fundal height in cm is within the expected range for your week of pregnancy.
Updated October 22, 2026
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Fundal Height Is Calculated
Fundal height is the distance in centimeters from the top of your pubic bone to the top of your womb (the fundus). From about 24 weeks, the number of centimeters roughly matches the number of weeks you are pregnant, so a tape measure gives your care team a quick check on your baby's growth¹ ². This calculator compares your reading with that rule and with an international fundal height standard.
What Fundal Height Measures
It measures the size of your womb, not your baby. The reading includes the baby, the placenta and the fluid around the baby, and your body shape affects it. It is a screening check, and it cannot tell you your baby's weight.
The Formula
Expected fundal height (cm) = weeks pregnant
Expected range = weeks pregnant plus or minus 2 cm
Wider range used by some clinics = weeks pregnant plus or minus 3 cm
INTERGROWTH-21st median (cm) = 5.133374 + 0.1058353119 x GA² - 0.0231295 x GA² x ln(GA)
INTERGROWTH-21st SD (cm) = 0.9922667 + 0.0258087 x GA
Cleveland Clinic uses plus or minus 2 cm¹ and Mayo Clinic plus or minus 3 cm after 24 weeks². The median and SD (spread) equations come from the INTERGROWTH-21st study of 4,239 women in eight countries; GA is weeks pregnant as a decimal³.
How This Calculator Computes Your Result
Enter your weeks and days, or your due date (the calculator counts back from 40 weeks), your fundal height in cm, and one baby or twins or more. Your weeks and days become a decimal (28 weeks 3 days is 28.4), which is your expected fundal height. You see your expected range, how far your reading is from it, your band, and your approximate INTERGROWTH-21st centile with the middle 80% of readings for your week³.
Results run from 24 weeks 0 days to 41 weeks 6 days; earlier weeks get a note instead. The INTERGROWTH-21st table is published to 40 weeks, so centiles after 40 weeks extend its equation. Twins get a note only, because fundal height is not reliable in twin pregnancies⁶.
What Your Result Means
Your reading compared with your weeks | Band | What usually happens next |
More than 3 cm below | Below the expected range | Often checked with an ultrasound scan |
2.1 to 3 cm below | Slightly below | Inside the wider range some clinics use; compared with earlier readings |
Within 2 cm either way | Within the expected range | Routine care continues |
2.1 to 3 cm above | Slightly above | Inside the wider range some clinics use; compared with earlier readings |
More than 3 cm above | Above the expected range | Often checked with an ultrasound scan |
A reading outside the range is a prompt for a closer look, not a diagnosis. Your care team may suggest an ultrasound, which measures the baby directly¹ ², and the pattern across visits matters more than one reading⁵.
Quick reference, worked out from the rule and the INTERGROWTH-21st equations³:
Weeks | Rule range (cm) | INTERGROWTH-21st median (cm) | Middle 80% of readings (cm) |
24 | 22 to 26 | 23.8 | 21.7 to 25.8 |
28 | 26 to 30 | 27.7 | 25.5 to 29.9 |
32 | 30 to 34 | 31.4 | 29.1 to 33.8 |
36 | 34 to 38 | 34.9 | 32.4 to 37.3 |
40 | 38 to 42 | 38.0 | 35.4 to 40.5 |
How to Measure Correctly
A midwife or doctor takes this measurement. The INTERGROWTH-21st study used these steps³:
Empty your bladder, then lie back.
A tape that does not stretch runs from the top edge of the pubic bone over the bump to the top of the womb.
The tape's numbers face away from the examiner until the end, so the expected number does not sway the reading.
UK guidance adds: record it to one decimal place and plot it on a chart⁵.
Why Your Reading Might Be Higher or Lower
A reading can measure large with a wrong due date, fibroids, a higher body weight, twins, extra fluid around the baby, a baby lying bottom down (breech) or a large baby¹. It can measure small if you are petite or have strong stomach muscles, have low fluid, or your baby has dropped into your pelvis, as well as when a baby is growing slowly¹. From about 36 weeks the measurement is less accurate¹, and on the INTERGROWTH-21st standard the median falls behind the week count, to about 38 cm at 40 weeks³.
How Accurate the Rule Is, and How UK Care Differs
The rule is a rough guide. Worked out from the INTERGROWTH-21st equations, about 75 in 100 pregnancies at 28 weeks fall within 2 cm of the week count, but fewer than half do at 40 weeks³. In a US study of women at 24 to 40 weeks, fundal height picked up only 3 of 7 babies whose scan weight was below the 10th percentile, and many babies it flagged were a normal size⁴.
In the UK, many maternity units plot each reading on a customised growth chart (GROW, from the Perinatal Institute) that adjusts for the mother's height, weight, ethnic origin and number of previous babies⁶. The Perinatal Institute calls the cm equals weeks rule "simply not true" and warns that accepting plus or minus 2 or 3 cm is unsafe, because a baby could stop growing for weeks and still pass as normal⁵. Readings that stop rising lead to a scan referral⁵. If your notes show a centile on a personalized chart, that chart takes priority.
Fundal Height by Week: The Rule and the INTERGROWTH-21st Standard
The dashed line is the centimeters-equals-weeks rule. The solid line is the international median, which falls behind the rule late in pregnancy.
- INTERGROWTH-21st median
- Rule (cm = weeks)
- Middle 80% of readings
Show data table
| Weeks pregnant | INTERGROWTH-21st median (cm) | Rule (cm = weeks) (cm) | Middle 80% of readings (cm) |
|---|---|---|---|
| 24 weeks | 23.8 | 24.0 | 21.7–25.8 |
| 28 weeks | 27.7 | 28.0 | 25.5–29.9 |
| 32 weeks | 31.4 | 32.0 | 29.1–33.8 |
| 36 weeks | 34.9 | 36.0 | 32.4–37.3 |
| 40 weeks | 38.0 | 40.0 | 35.4–40.5 |
A Note on Accuracy
This calculator uses a rule of thumb and an international average chart. It cannot see your earlier readings or the personalized chart your midwife may use, and readings differ between examiners. It is for one baby only and is not a diagnosis. Separate from fundal height, NHS advice is to call your midwife or maternity unit straight away if your baby is moving less than usual or their usual pattern changes, and not to wait until the next day⁷.
Frequently Asked Questions
What is a normal fundal height for my weeks?
From 24 weeks, a normal fundal height in cm is usually close to your weeks of pregnancy, within about 2 cm either way¹ ². Some clinics accept 3 cm either way².
How accurate is fundal height measurement?
It is a low-cost screening check, not a precise test. In one study it picked up fewer than half of the small babies found on ultrasound⁴, so an unusual reading leads to a scan, not a conclusion.
What happens if my fundal height is measuring small or large?
Your midwife or doctor will compare it with your earlier readings and may arrange an ultrasound to check your baby's growth and fluid² ⁵. Many readings outside the range have simple causes, such as body shape, the baby's position or a due date that is slightly off¹.
When do they start measuring fundal height?
Most care teams compare fundal height with your weeks from about 24 weeks². The Perinatal Institute, which runs the UK's customised charts, suggests starting at 26 to 28 weeks⁵.
Sources
Fundal Height, Cleveland Clinic, 2025
Fundal Height: An Accurate Sign of Fetal Growth?, Mayo Clinic, 2026
International Standards for Symphysis-Fundal Height (INTERGROWTH-21st), Papageorghiou et al., 2016
Diagnostic Accuracy of Fundal Height to Screen for Fetal Growth Abnormalities, Haragan et al., 2015
Fundal Height Measurements FAQ, Perinatal Institute
Customised Charts FAQ, Perinatal Institute
Your Baby's Movements, NHS, 2024