Your spleen is a small but hard-working organ hidden behind your stomach and under your diaphragm. It acts as a filter for your blood. Old, damaged, or abnormal red blood cells are caught in a maze of narrow tunnels within the spleen. Healthy red blood cells easily pass through the spleen and continue to circulate in your bloodstream.

The spleen can also filter out certain bacteria or viruses from your blood in support of the body’s immune system. When a disease-causing microorganism enters the bloodstream, your spleen and lymph nodes produce lymphocytes, a type of white blood cell capable of making antibodies to fight infections.

Unlike most other organs in your body, your spleen changes in size throughout your life — usually in response to illness or injury. A viral infection, such as mononucleosis, or a bacterial infection, such as syphilis, are among the conditions that can lead to an enlarged spleen.

The size of a normal, healthy spleen can vary considerably from person to person. Your sex and height can also affect its size. In general, an adult spleen is about 5 inches long, 3 inches wide, 1.5 inches thick, and weighs about 6 ounces.

Women tend to have smaller spleens than men, and taller people tend to have larger spleens than shorter people. In a study in the journal Radiology, researchers suggested that aside from men generally being taller than women, men also typically have greater red cell mass than women.

Your spleen, like the rest of your body, grows with age. Once you reach adulthood, however, your spleen tends to shrink slightly with each passing decade. The following is a list of the upper limit of normal spleen length by age up to 15 years. For boys and girls, there is relatively little difference in size, according to a study published in the American Journal of Roentgenology. The average spleen length by age was up to:

AgeLength
3 months1.9 in. (6.0 cm)
6 months2.6 in. (6.5 cm)
12 months2.8 in. (7.0 cm)
2 years3.1 in. (8.0 cm)
4 years3.5 in. (9.0 cm)
6 years3.7 in. (9.5 cm)
8 years3.9 in. (10.0 cm)
10 years4.3 in. (11.0 cm)
12 years4.5 in. (11.5 cm)
15 years4.7 in. (12.0 cm) for girls, 5.1 in. (13.0 cm) for boys

In a separate study of adults, researchers found that spleen length changed very little from the late teen years through ages 40 to 50.

For women, average spleen length was:

AgeLength
31 to 40 years4.9 in. (12.4 cm)
41 to 50 years4.8 in. (12.2 cm)
60 to 70 years4.7 in. (12.1 cm)
71 to 80 years4.4 in. (11.2 cm)
81 to 88 years4.0 in. (10.4 cm)

For men, average spleen length topped out at:

AgeLength
31 to 40 years4.7 in. (12.1 cm)
41 to 50 years5.3 in. (13.4 cm)
60 to 70 years4.5 in. (11.5 cm)
71 to 80 years4.4 in. (11.2 cm)
81 to 88 years4.6 in. (11.7 cm)

There is great variability in spleen size from person to person, with age, height, and sex all affecting spleen length. Other studies have found slightly different averages. The key to remember is that your spleen grows steadily during childhood, slows its growth into adulthood, and then shrinks in older age.

Disease or other circumstances can affect spleen size at any age. The spleen can also hold extra blood. Depending on how much is being held in reserve at any one time, the length and volume of the spleen can change. The reserve is helpful if you ever have a medical emergency and lose blood. The extra blood can help keep blood flowing for a short time until the bleeding is stopped.

During a physical examination, your doctor can usually tell if your spleen is enlarged. A blood test to check your levels of red blood cells, white blood cells, and platelets may also be ordered to help diagnose the cause of a spleen enlargement.

Imaging tests, including ultrasound, help measure the size of your spleen and whether it’s crowding your other organs.

An abdominal ultrasound is often preferred for evaluating the spleen because it’s easy to do and doesn’t require any radiation. Ultrasound uses sound waves to create images of inside the body on a computer screen. An ultrasound “wand” is rubbed on the outside of the belly, which is coated with a special gel. This gel helps transmit the sound waves through the skin and to the parts inside the body.

Ultrasound can usually measure the length of the spleen along a center line (axis) accurately. It can also measure the width and thickness of the spleen, which can typically tell the doctor whether the organ is abnormally large or small. In most cases, however, the concern is about an enlarged spleen.

An abdominal ultrasound can help detect other conditions, too. Some of them include:

Slight variances in spleen size are common and not a cause for concern. However, if you suspect your spleen is enlarged or you’re having any organ-related problems, see a doctor soon. If an infection is causing this temporary enlargement of the spleen, the sooner you get it diagnosed and treated, the better.

Treating the underlying cause of your spleen growth will usually cause it to return to a normal, healthy size. In very serious cases of spleen dysfunction, the organ can be removed. You will be at greater risk for infections, but that will only mean it’s even more important to keep up to date with vaccinations and other preventive steps, such as washing your hands thoroughly and regularly or avoiding people who may have a contagious infection.