There is no formal clinical definition of occasional constipation, and clinicians, patients, and diagnostic criteria define it differently.
However, chronic constipation is defined by the most recent Rome criteria: 
- Presence of two or more of the following symptoms:
- - Straining during at least 25% of defecations
- - Lumpy or hard stools in at least 25% of defecations
- - Sensation of incomplete evacuation for at least 25% of defecations
- - Sensation of anorectal obstruction/blockage for at least 25% of defecations
- - Manual maneuvers to facilitate at least 25% of defecations (such as digital evacuation, support of the pelvic floor)
- - Fewer than three bowel movements a week
- Loose stools are rarely present without the use of laxatives
- Criteria have to have been met for the previous three months, with the onset of symptoms six months prior to diagnosis
Occasional constipation is often described as a departure from an individual's normal bowel movements and/or the presence of the same symptoms as chronic constipation (listed above). However, if symptoms last for 7 days or longer, a physician should be consulted.
The Bristol ScaleDownload
The Bristol Scale (referred to in the UK as the Meyers Scale) was developed at the University of Bristol. It can be used to monitor change in bowel consistency and helps the patient describe bowel movements in an objective and minimally embarrassing manner.
Types 1 and 2 on the Bristol Scale indicate constipation. Types 3 and 4 are the "ideal stools", especially the latter, as they are the easiest to defecate. Finally, types 5 - 7 tend towards diarrhea.
Separate, hard lumps, like nuts (hard to pass)
Sausage-shaped but lumpy
Like a sausage but with cracks on its surface
Like a sausage or snake, smooth and soft
Soft blobs with clear-cut edges (passed easily)
Fluffy pieces with ragged edges, a mushy stool
Watery, no solid pieces. Entirely liquid
The Bristol Stool Scale was created by Lewis SJ, Heaton KW. Scand J Gastroenterol. 1997.