Normal kidney size is expressed as an average, since actual sizes vary from person to person. In fact, an individual's two kidneys are normally not identical in size.
Some studies indicate that kidney size is positively correlated to age and body size (height, weight, body mass index). The greater the body size, the larger the kidneys tend to be.
As young children mature and their kidneys develop, they increase in size. The kidneys become fully developed in the early stages of adulthood, and tend to decrease in later year... Typically, renal size decreases in older persons.
When fully developed, the kidneys are roughly the size of a fist.
In more precise measurements, the average size of an adult human kidney is about 10 to 13 cm (4 to 5 inches) long, approximately 5 to 7.5 cm (2 to 3 inches) wide and about 2 to 2.5 cm (1 inch) thick.
On average, a kidney weighs approximately 150 to 160 grams and, together, both kidneys weigh about 0.5 percent of total body weight. Usually, the left kidney is slightly larger than the right.
These measurements and weights represent the typical ranges of a healthy, adult human kidney.
Actual kidney size is directly correlated with, height, age and BMI (body mass index). Therefore, taller people with greater BMI tend to have larger kidney dimensions than shorter persons with less BMI. Also, as people age, there is a tendency for their kidneys to shrink a bit.
Determining the normal size of children's kidneys can be quite challenging, given the wide variation in children's sizes and rate of development. Some studies have compared renal length with children's ages, to determine the typical kidney size of children. The results show the following average renal lengths, based on children's ages:
Typically, the kidneys are fully developed in the early twenties (about 23 to 25 years of age). There should be very little or no changes to the size of the kidneys, after this age.
Kidney disease is an important factor that may affect kidney size. In fact, the size of a kidney and changes in its size can provide indications of renal problems.
For instance, polycystic disease and hydronephrosis (a condition where fluids accumulate inside the kidney) can cause distension (enlargement) of the kidneys.
Other chronic renal conditions can affect kidney size and cause the kidneys to decrease in size. This is known as atrophy and usually occurs over a period of time (usually years). Alport Syndrome, Chronic Glomerulonephritis and Hypertensive Nephrosclerosis are examples of conditions, which may cause atrophy.
If kidney dimensions are found to be outside the range of what is considered normal kidney size, further investigations are usually done to determine whether kidney disease is present.