Human brains grow most rapidly just after birth and reach half their adult size within three months, according to a study in JAMA Neurology.
Using advanced scanning techniques, researchers found male brains grew more quickly than those of female infants.
Areas involved in movement developed at the fastest pace. Those associated with memory grew more slowly.
Scientists say collating this data may help them identify early signs of developmental disorders such as autism.
Sizing up development
For centuries doctors have estimated brain growth using measuring tape to chart a baby's head circumference over time.
Any changes to normal growth patterns are monitored closely as they can suggest problems with development.
But as head shapes vary, these tape measurements are not always accurate.
Led by scientists at the University of California, researchers scanned the brains of 87 healthy babies from birth to three months.
They saw the most rapid changes immediately after birth - newborn brains grew at an average rate of 1% a day. This slowed to 0.4% per day at the end of the 90-day period.
Researchers say recording the normal growth trajectory of individual parts of the brain might help them better understand how early disorders arise.
They found the cerebellum, an area of the brain involved in the control of movement, had the highest rate of growth - doubling in size over the 90-day period.
The slowest region measured was the hippocampus, a structure that plays an important part in how memories are made.
Scientists suggest this could mirror the relative significance of these skills as a young infant.
Dr Martin Ward Platt, a consultant paediatrician at the Royal Victoria Infirmary in Newcastle, who was not involved in the research, told the BBC: "This is the first time anyone has published accurate data about how babies' brains grow that is not based on post-mortem studies or less effective scanning methods.
"The study should provide us with useful information as this is an important time in development.
"We know, for example, if there are difficulties around the time of birth, a baby's growth can fall away in the first few months."
Looking at babies who were born early, researchers noticed their brains were 4% smaller than the brains of babies born at full term.
And despite growing at a quicker rate than babies born on time, their brains were still 2% smaller at the end of three months.
Scientists will now investigate whether alcohol and drug consumption during pregnancy alters brain size at birth.