Bristol Stool Scale

The Bristol Stool Scale (also called the Bristol Stool Chart) is a simple medical tool that sorts human poop into seven types, from hard lumps to watery liquid. It was developed by Dr. Stephen Lewis and Dr. Ken Heaton at the University of Bristol and published in 1997 as an easy way to describe stool consistency — which closely reflects how long stool has spent moving through your gut.

Doctors use it to discuss bowel habits without awkward guesswork, and it's just as useful at home. Knowing your usual Bristol type — and noticing when it changes — is one of the easiest ways to keep an eye on your digestive health.

The 7 Bristol Stool types at a glance

Types 1 & 2: hard and lumpy (constipation)

Hard, pellet-like stool (type 1) or a lumpy sausage (type 2) means stool has stayed in the colon too long. The longer it sits, the more water the colon reabsorbs, leaving it dry and difficult to pass. Common contributors include too little fiber, not drinking enough fluid, low physical activity, ignoring the urge to go, and some medications. Straining, a feeling of incomplete emptying, and infrequent bowel movements often come with these types.

Types 3 & 4: the healthy range

This is what you're aiming for. A type 3 stool is formed with small surface cracks; a type 4 is smooth and soft, shaped like a sausage or snake. Both pass easily without straining and suggest a comfortable transit time and a reasonable balance of fiber and fluid. If most of your bowel movements look like this, your routine is probably working well.

Types 5, 6 & 7: soft to watery (loose stool and diarrhea)

Type 5 is soft blobs that pass easily — sometimes just a sign of low fiber, sometimes the early edge of looseness. Types 6 and 7 are mushy to fully liquid and indicate stool is moving through the gut too quickly for water to be absorbed. Short-lived episodes are often caused by an infection ("stomach bug"), food intolerance, a dietary change, stress, or medication. Diarrhea that lasts more than a couple of days, or comes with other symptoms, deserves attention because of the risk of dehydration.

What changes your Bristol type?

• Fiber: Soluble and insoluble fiber add bulk and hold water, nudging hard stool toward the type 3–4 range.
• Hydration: Fluid keeps stool soft; too little tips you toward types 1–2.
• Movement: Physical activity helps the gut keep things moving.
• Routine & stress: Travel, schedule changes, and stress can shift your type in either direction.
• Medication & conditions: Iron and some painkillers harden stool; many other drugs and conditions loosen it.

Because so many everyday factors play a role, an occasional off day is normal. What matters more is your usual pattern and any lasting change from it.

When to see a doctor

The Bristol scale describes consistency — it does not diagnose disease. Talk to a healthcare professional if you notice:

• Blood in your stool, or black, tarry stool
• A persistent change in your normal pattern lasting more than 2–3 weeks
• Diarrhea that lasts more than a few days or causes signs of dehydration
• Unexplained weight loss, ongoing abdominal pain, or fever
• Stool that is pale, clay-colored, or greasy and hard to flush

These can have simple explanations, but they're worth checking — especially when they're new or persistent.

Tracking your Bristol type with PoopID

The hardest part of using the scale is remembering what's normal for you. PoopID does that automatically: snap a photo and it identifies your Bristol Stool type, folds it into a 0–100 gut health score, and flags patterns worth watching — privately, on your iPhone. Over time you get a clear picture of your trend instead of relying on memory.

• Sources:
• Lewis SJ, Heaton KW. "Stool form scale as a useful guide to intestinal transit time." Scandinavian Journal of Gastroenterology, 1997.
• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) — Constipation & Diarrhea. niddk.nih.gov
• NHS — Constipation, Diarrhoea. nhs.uk