This Red blood cell distribution width (RDW) calculator determines the distribution width of RBC given the MCV value and its standard deviation. Below the form you can find out more on the RDW-SD range as well as info on the complete blood count.


Standard dev. of MCV:*
Mean Corpuscular Volume:*

How does this Red blood cell distribution width (RDW) calculator work?

This health calculator estimates the variation of RBC width, one of the results in the standard complete blood count. The Red blood cell distribution width (RDW) calculator uses the standard deviation of MCV values along with the actual mean corpuscular volume value in the following formula:

RDW-SD = (Std Dev of MCV x 100 / MCV)

The standard size of red blood cells varies between 6 – 8 microns. However, their normal reference range for volume is between 11 – 15%, and RDW-SD = 39 – 46 fL, meaning the width of the volume curve. There are two types, either the RDW-CV when reported as coefficient of variation or RDW-SD, the more common version, the one used above, when reported as standard deviation.

The RDW-CV formula is as follows: 1 SD of RBC volume / MCV x 100%.

There are several disorders that cause a RBC size variation. It is important to note whether these high levels are associated to low, normal or high MCV.

When both red blood cell parameters are increased, one of the causes might be liver disease with or without hemolytic anemia. High RDW and low MCV can be due to iron deficiency that in turn causes a decrease in hemoglobin.

High RDW values are indicative of a greater variation and are often associated with adverse outcomes, especially in patients with heart failure or raised cardiac risk.

Studies have shown a close correlation between RDW and the risk of carotid artery atherosclerosis in patients diagnosed with hypertension.

RDW and MCV in anemia

RDW is often used in the diagnosis of anemia causes, alongside with MCV. The mean corpuscular volume measures the average volume of red blood cells and provides information on the whole dimension variation.

MCV is obtained through the multiplication of the volume of blood to the actual proportion of cellular blood (meaning hematocrit). During the process, centrifugation insures erythrocytes sediment.

When the mean corpuscular volume is below the normal range, the patient might suffer from microcytic anemia, if MCV is in the normal range but anemia is still suspected, there might be a case of normocytic anemia. The most common cause of this type of anemia is iron deficiency. Above average corpuscular volumes are indicative of macrocytic anemia. Elevated MCV is also associated with alcoholism and vitamin B12 deficiency.

However, not all RDW elevations are consistent with anemia, even normal levels can underpoint chronic disease, hereditary spherocytosis or certain hereditary hemoglobinopathies.

The Standard Complete Blood Count

The CBC is a laboratory blood test, also known as the full blood count FBC, aiming at describing blood parameters in terms of cell components, sizes and protein concentration. CBC is used to screen and monitor the overall health of the patient and is also used in cases that require blood transfusion.

Count of erythrocytes, leukocytes and thrombocytes, meaning red blood cells, white blood cells and platelets are the most common parameter and have diagnostic value.

The procedure involves the drawing of the blood, mixing it with anticoagulant, usually EDTA and then part of the sample is investigated under the microscope while the rest goes in an automated analyzer.

Other tests performed include the quantity of hemoglobin in the blood in g/dL, hematocrit percentage which is the packed cell volume, MCV, MCH (mean corpuscular hemoglobin) and RDW. Most complete exams also perform neutrophil granulocytes count, lymphocytes, monocytes, eosinophil and basophil granulocytes counts.


1) Red Cell Distribution Width in Family Practice Notebook [available online].

2) Wen Y. (2010) High red blood cell distribution width is closely associated with risk of carotid artery atherosclerosis in patients with hypertension. Exp Clin Cardiol; 15(3): 37–40.

3) Balta S, Demirkol S, Aparci M, Yildirim AO, Ozturk C, Celik T.(2015) Red blood cell distribution width: Just one of many things to consider. Int J Cardiol;203:438-439.

4) Buttarello M, Plebani M.(2008) Automated blood cell counts: state of the art. Am J Clin Pathol; 130(1):104-16.

11 Nov, 2015