How to Make a Fishbone (Ishikawa) Diagram, Step by Step
- timothyferguson1
- Jun 13
- 4 min read
June 13, 2006
The fishbone diagram — also called the Ishikawa or cause-and-effect diagram — is the most-used brainstorming tool in root cause analysis, and for good reason: it forces a team to look at the whole range of possible causes instead of locking onto the first one that comes to mind. This guide shows you how to build one from scratch, with a worked example and the common mistakes to avoid.
Where does this fit in the bigger picture? See our root cause analysis guide.
What is a fishbone diagram?
A fishbone diagram is a visual map of the possible causes of a problem. The “head” of the fish is the problem (the effect); the “spine” runs to it; and “bones” branch off the spine, each holding a category of causes. The finished diagram looks like a fish skeleton — hence the name. It was popularized by Kaoru Ishikawa, which is why you’ll also see it called an Ishikawa diagram.
Its strength is breadth: by organizing causes into categories, it nudges you to consider areas you’d otherwise skip.
Before you start: define the problem
A fishbone is only as good as the problem written in its head. If the effect is vague (“quality issues”), every branch will be vague too. Spend a few minutes writing a clear, measurable problem statement first.
Tip: Our Problem Statement Builder | https://app.fsquaredconsultinggroup.com can hand a sharp statement straight to the fishbone head.
Step 1 — Write the problem in the head
Put your problem statement in the box at the right (the head). Keep it factual and measurable — for example: “~6% of Line 3 cartons ship with unsealed top flaps since the May changeover.” Everything that follows is in service of explaining that effect.
Step 2 — Draw the spine and choose your categories
Draw a horizontal arrow (the spine) pointing to the head, then add diagonal “bones.” Each bone is a category of causes. The most common category set in manufacturing is the 6 Ms:
• People (Manpower) — skills, training, staffing, fatigue
• Process (Methods) — procedures, sequence, handoffs
• Equipment (Machines) — tooling, maintenance, calibration
• Materials — inputs, quality, specification, storage
• Environment — lighting, temperature, layout, noise
• Management — priorities, communication, resourcing
Service teams sometimes use the 4 Ss or a Human and Organizational Performance set instead. Pick the categories that fit your work — the point is structure, not dogma.
Step 3 — Brainstorm causes onto the bones
Take each category in turn and ask: “What here could contribute to this effect?” Write every candidate cause as a smaller bone off that category. Two ground rules:
• Breadth before judgment. Capture ideas first; don’t debate them yet. A cause you dismiss too early might be the real one.
• Causes, not solutions. “No standard changeover procedure” is a cause; “write a procedure” is a solution for later.
For deeper branches, you can ask “why?” on a cause to add sub-causes — a mini bridge into your 5 Whys later.
Step 4 — Look for patterns and cluster
Step back and read the whole diagram. Look for:
• Causes that repeat across categories — often a sign of a systemic factor.
• Clusters of related causes you can group.
• Branches with the most plausible, evidence-backed causes — these are your candidates to drill.
Step 5 — Pick the likely causes to investigate
A fishbone gives you possibilities, not proof. Circle the two or three most likely causes — the ones with supporting evidence or the biggest potential impact — and take them into a deeper analysis to confirm the true root.
A worked example
Problem (head): ~6% of Line 3 cartons ship with unsealed top flaps since the May changeover.
• People: new operators undertrained on the changeover; shift-handoff gaps
• Process: no standard changeover procedure; missing inspection checkpoint
• Equipment: sealer temperature drifts; worn cutting blades
• Materials: carton film thickness varies by lot; adhesive past shelf life
• Environment: high humidity on the night shift
• Management: throughput prioritized over quality checks
The strongest, evidence-backed branches here — no standard changeover procedure and sealer temperature drift — become the candidates for a 5 Whys.
Common mistakes to avoid
• Vague problem in the head — fix it before you draw a single bone.
• Writing solutions instead of causes — keep the fix out of it for now.
• Stopping at the obvious category — push through all of them, even the quiet ones.
• Treating the diagram as the answer — it’s a map of suspects, not a verdict. Drill to confirm.
Build one free in minutes: The F Squared fishbone tool lets you brainstorm across 6M or HOP categories, cluster related causes, and (on Pro) let AI surface causes you might have missed — then carry the strongest one straight into a 5 Whys. Try it free →
Prefer paper? The free RCA Starter Kit includes a printable fishbone template.
Frequently asked questions
What is a fishbone diagram used for?
To brainstorm and organize the possible causes of a problem into categories, so a team considers the full range of factors before drilling into the most likely ones.
What are the 6 Ms of a fishbone diagram?
People (Manpower), Process (Methods), Equipment (Machines), Materials, Environment, and Management — the most common category set for organizing causes.
Is a fishbone diagram the same as an Ishikawa diagram?
Yes. “Fishbone,” “Ishikawa,” and “cause-and-effect diagram” all refer to the same tool, named after Kaoru Ishikawa.
How many causes should a fishbone have?
As many as the team can think of — breadth is the point. There’s no target number; aim to fully populate each category, then narrow to the few most likely causes to investigate.
What’s the next step after a fishbone?
Pick the most likely cause(s) and run a 5 Whys to confirm the systemic root, then document the fix in an A3.
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