Fundal Height Calculator (cm vs weeks of pregnancy, ±2 cm rule)

Understanding the fundal height calculator — concept and principle

Fundal height is the distance from the top of the pubic bone to the top of the uterus, measured with a tape at antenatal visits. This calculator compares your measurement with your weeks of pregnancy using the common rule that, from about 20 to 36 weeks, centimetres roughly equal weeks.

Centimetres ≈ weeks: with the default inputs the result is −1 cm (within ±2 cm).

How it is calculated

Weeks suggested by fundal height = fundal height (cm)

Difference = fundal height − weeks of pregnancy

Expected range at your week = weeks − 2 cm to weeks + 2 cm

A difference within ±2 cm counts as as expected.
The rule applies from 20 to 36 weeks; the calculator tells you if your week is outside it.

The principle

As the baby, placenta and fluid grow, the top of the uterus rises from the pelvis towards the ribs at a fairly steady rate of about 1 cm a week in the middle of pregnancy. At about 20 weeks it reaches the navel. Before 20 weeks the uterus is too low for a reliable tape measure, and after about 36 weeks the baby often moves down into the pelvis, so the measurement levels off. The tape is a simple, cheap screening check for growth that is too slow or too fast.

Worked example

Default inputs: fundal height 30 cm at 31 weeks.

Weeks suggested by fundal height = 30.
Difference = 30 − 31 = −1 cm.
Expected range = 31 − 2 to 31 + 2 = 29 to 33 cm.
−1 is within ±2 → Yes — within ±2 cm; 31 weeks is in 20–36 → rule applies.

How to read the result

Where does your result fall?

A measurement inside the range is reassuring. One that is larger or smaller, or that stops increasing between visits, is usually followed by an ultrasound scan to check the baby's growth and the fluid volume. The trend over several visits matters more than one number.

Common mistakes

Measuring with a full bladder, which can add a centimetre or more.
Comparing measurements taken by different people with different techniques.
Applying the rule before 20 weeks or after 36 weeks.

Keep in mind: This is not a diagnosis. Body build, fibroids, the baby's position, twins and fluid volume all affect fundal height. Follow your midwife's or doctor's advice.

Frequently asked questions

What is a normal fundal height at 32 weeks?

Roughly 30–34 cm.

Why is my measurement 3 cm off?

It may reflect measurement error, your build or the baby's position, or a growth difference; a scan can clarify.

Can I measure fundal height myself?

It is possible but difficult to do accurately. It is best done by your midwife or doctor in the same way each time.

Sources: Cleveland Clinic, "Fundal Height" (Health Library)

Checked 9 Nov 2026. Cleveland Clinic, “Fundal Height” (Health Library, Diagnostics 22294): centimetres approximately equal weeks from about 20 to 36 weeks, ±2 cm (example 30–34 cm at 32 weeks).

Your numbers