👶

Fundal Height Calculator

Compare a fundal-height measurement with the expected value for your gestational week (McDonald’s rule) and see whether it falls in the normal ±2–3 cm band.

Gestational age

Measured fundal height

Loading calculator…

How it works

Expected fundal height (cm) ≈ gestational age in weeks, from 20 to 36 weeks (McDonald’s rule)

Between about 20 and 36 weeks the distance from pubic bone to the top of the uterus grows roughly 1 cm per week, so the centimetre reading tracks the week. Readings more than 2–3 cm off the expected value prompt a growth scan — the measurement itself is a screen, not a diagnosis. Position, bladder fullness, twins and body shape all shift it.

Worked example

28 weeks and 30 cm: +2 cm, still inside the ±2 cm band.

Frequently asked questions

Why is it measured from 20 weeks?

Before 20 weeks the uterus is still below or just at the navel and the rule is unreliable; near term the head engages and the height can plateau or drop.

My measurement is 4 cm off — should I worry?

It is a reason for a scan, not a verdict. Fluid levels, baby position and measurement technique explain many discrepancies.

Related calculators

Pregnancy Week Calculator

Find out how many weeks and days pregnant you are — from your last period, due date, conception, IVF transfer or an ultrasound — with your pregnancy week, month, trimester, days remaining and a milestone timeline, today or on any date.

Fetal Weight Percentile Calculator

Estimate what percentile an ultrasound estimated fetal weight falls in for its gestational week, using Hadlock reference growth.

Baby Size by Week Calculator

See your baby’s typical length, weight and fruit-sized comparison for any pregnancy week from 4 to 40.

Educational estimate only — your midwife or doctor will confirm dates and advice for your pregnancy.