Bristol Stool Scale

The Bristol Stool Scale or Bristol Stool Chart is a medical aid designed to classify the faeces form into seven groups. It was developed by Heaton and Lewis at the University of Bristol and was first published in the journal Scand J Gastroenterol in 1997. Because the form of the stool depends on the time it spends in the colon, there is a correlation between the colonic transit time and the stool type. 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, with 3 and 4 being the "ideal stools" especially the latter, as they are the easiest to pass. 5-7 being further tending towards diarrhea.

(From Wikipedia. http://en.wikipedia.org/wiki/Bristol_Stool_Scale)