The Bristol Stool Scale or Bristol Stool Chart is a medical aid designed to classify the form of human faeces into seven categories. Sometimes referred to in the UK as the "Meyers Scale", it was developed by Dr. Ken Heaton at the University of Bristol

University of Bristol

The University of Bristol is a public research university located in Bristol, United Kingdom. One of the so-called "red brick" universities, it received its Royal Charter in 1909, although its predecessor institution, University College, Bristol, had been in existence since 1876.The University is...

 and was first published in the Scandinavian Journal of Gastroenterology in 1997. The authors of that paper concluded that the form of the stool is a useful surrogate measure of colon

Colon (anatomy)

The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...

 transit time. That conclusion has since been challenged as having limited validity, and only in types 1 and 2 when the subject is not constipated. However, it remains in use as a research tool to evaluate the effectiveness of treatments for various diseases of the bowel, as well as a clinical communication aid.

The seven types of stool are:

• Type 1: Separate hard lumps, like nuts (hard to pass)
• Type 2: Sausage-shaped, but lumpy
• Type 3: Like a sausage but with cracks on its surface
• Type 4: Like a sausage or snake, smooth and soft
• Type 5: Soft blobs with clear cut edges (passed easily)
• Type 6: Fluffy pieces with ragged edges, a mushy stool
• Type 7: Watery, no solid pieces. Entirely liquid

Types 1 and 2 indicate constipation

Constipation

Constipation refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation...

, with 3 and 4 being the "ideal stools", especially the latter, as they are the easiest to defecate

Defecation

Defecation is the final act of digestion by which organisms eliminate solid, semisolid or liquid waste material from the digestive tract via the anus. Waves of muscular contraction known as peristalsis in the walls of the colon move fecal matter through the digestive tract towards the rectum...

, and 5–7 tending towards diarrhoea

Diarrhea

Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

.