Fundal height, or McDonald's rule, is a measure of the size of the uterus used to assess fetal growth and development during pregnancy. It is measured from the top of the mother's uterus to the top of the mother's pubic symphysis. Fundal height, when expressed in centimeters, roughly corresponds to gestational age in weeks between 16 and 36 weeks for a vertex fetus. When a tape measure is unavailable, finger widths are used to estimate centimeter (week) distances from a corresponding anatomical landmark. However, landmark distances from the pubic symphysis are highly variable depending on body type. In clinical practice, recording the actual fundal height measurement from the palpable top of the uterus to the superior edge of the pubic symphysis is standard practice beginning around 20 weeks gestation.

Most caregivers will record their patient's fundal height on every prenatal visit. Measuring the fundal height can be an indicator of proper fetal growth and amniotic fluid development.

Knowledge of gestational age may impact how the height is measured.