A Gantt chart is a project schedule drawn as horizontal bars on a calendar. Each row is a task, each bar starts on the task's start date and ends on its finish date, and arrows or ordering show which tasks have to finish before others can begin. One glance shows what is happening when, what overlaps, where the project is waiting on something, and whether it is on track. It is the standard planning view for any improvement project longer than a few days: a plant-wide 5S rollout, a floor marking project across several areas, a TPM pilot, or the preparation for a kaizen event.
Reading a Gantt chart
- Rows are tasks, usually grouped under summary rows for each phase.
- The horizontal axis is time: days for a short project, weeks for a long one.
- Bars show when each task starts and ends. Bar length is duration.
- Dependencies are links between tasks. The most common one is finish-to-start: B cannot begin until A is done. A dependency is why a bar starts where it does.
- Milestones are zero-duration events, drawn as diamonds: charter approved, materials delivered, event complete, 30-day audit.
- Progress is shown by filling in part of each bar, with a vertical line for today, so slippage is visible as a bar that is behind the line and not full.
- The critical path is the chain of dependent tasks with no slack. Any delay on it delays the whole project. Good charts highlight it.
A short history
Karol Adamiecki, a Polish engineer, drew the first schedule charts of this type in 1896 and called them harmonograms, but published mainly in Polish and Russian. Henry Gantt, an American mechanical engineer who had worked with Frederick Taylor at Midvale Steel, developed his version independently around 1910 to 1915 for scheduling production and later for U.S. military shipbuilding and arsenal work during the First World War. The chart carried his name because his were the versions that spread. They were drawn by hand and redrawn whenever the schedule changed, which limited them to projects stable enough to be worth the effort, until spreadsheets and project software made updating trivial.
Building one for an improvement project
- List the tasks. Break the project into pieces small enough that each has one owner and a duration you can estimate, usually a few hours to a few days. Group them under phases. This is the work breakdown structure; the Gantt chart is a view of it.
- Estimate durations. Working days, not calendar days, and based on how long the task actually takes someone who also has a regular job. Past projects are the best source; see resource management on tracking actuals.
- Set dependencies. For each task, what has to be done first. Only the real ones: material has to arrive before marking can start; the layout has to be approved before material is ordered. Tasks with no dependency between them can overlap.
- Assign owners. One name per bar. A bar with no owner is a wish.
- Add milestones. The approval points, the deliveries, the event dates, the audit.
- Find the critical path and look hard at it. Those are the tasks where a day lost is a day lost for the project. Add buffer there, not everywhere.
- Check it against capacity. If the same person owns three overlapping bars, the chart is fiction. Move bars or get help.
- Post it and update it. On the project board or the event room wall, marked up weekly. A chart that is not updated stops being believed within two weeks.
Example: a floor marking project
Marking one warehouse area (aisles, pedestrian lane, keep-clear zones, pallet locations) over four weeks, with the aisle closure on a weekend. Illustrative durations.
| Task | Owner | Wk 1 | Wk 2 | Wk 3 | Wk 4 |
|---|---|---|---|---|---|
| Plan | |||||
| Measure area and draft layout | M. Ortiz | ||||
| Review with operators and safety | M. Ortiz | ||||
| ◆ Layout approved | J. Lee | ◆ | |||
| Order tape, signs, mirror | Purchasing | ||||
| Prepare | |||||
| Clear and deep-clean floor | D. Shift | ||||
| Schedule weekend closure, notify adjacent areas | M. Ortiz | ||||
| ◆ Materials delivered | Purchasing | ◆ | |||
| Install | |||||
| Lay out and apply marking (weekend) | Team | ||||
| Install signs and mirror | Maintenance | ||||
| Sustain | |||||
| Toolbox talk, all shifts | Supervisors | ||||
| Post color legend, add to 5S audit | M. Ortiz | ||||
| ◆ 30-day audit | M. Ortiz | ◆ (wk 8) |
Reading it: the critical path runs layout → approval → order → delivery → weekend install. If the mirror ships late, the install slips a week, because the closure is already scheduled. The floor cleaning and the closure notice overlap with the order lead time because they do not depend on it. Everything in week 4 depends on the install, so the install weekend is the date to protect.
Gantt chart, kanban board, or timeline?
| Gantt chart | Kanban board | Timeline / milestone chart | |
|---|---|---|---|
| Best for | Projects with dependencies and a deadline | Continuous flow of tasks with no fixed end | Communicating key dates to people who do not need the detail |
| Shows | When each task happens and what it waits on | What stage each task is in right now | Milestones only |
| Does not show | Current status without updating | Dates, durations, dependencies | Tasks, owners, dependencies |
| Use it for | Rollouts, events with preparation, anything with ordering and lead times | Daily kaizen, maintenance backlogs, follow-up lists | Sponsor updates, the plant-wide improvement calendar |
Many teams run both: a Gantt chart for the project plan, a board for the day-to-day work inside it. A single-day kaizen or a two-task job does not need a Gantt chart. See project timelines for the lighter-weight version.
Common mistakes
- Too much detail. A 200-row chart for a four-week project will not be maintained. Tasks of half a day to a week; anything smaller is a checklist inside the task.
- Dependencies that are not real. Linking everything in sequence stretches the schedule and hides what could run in parallel.
- No owners. A bar without a name is nobody's job.
- Calendar days instead of working days, and estimates that assume the owner has nothing else to do.
- Buffer everywhere. Padding every task makes the schedule long and still late, because the padding gets consumed. Put buffer on the critical path and at milestones.
- Not updating it. The chart is the plan only as long as it reflects reality. Weekly at minimum; daily during an event.
- Treating it as fixed. When a task slips, the chart's job is to show what else moves. Re-baseline, tell the stakeholders, and move on. See scope creep for the version of this problem where the tasks multiply instead of slipping.
Tools
A spreadsheet is enough for most plant projects: tasks down the left, weeks across the top, shaded cells for bars. It is the most shareable format and the easiest to print for the wall. Dedicated project software (Microsoft Project, Smartsheet, Asana, and similar) adds automatic dependency handling, critical path calculation, and resource leveling, which pay off once a project has more than a few dozen tasks or shares people across several projects. Whichever you use, the posted paper copy at the gemba is what the team actually looks at.
Frequently asked questions
What does a Gantt chart show?
Tasks as bars on a time axis, so you can see when each one starts and ends, which ones overlap, which depend on others, where the milestones are, and how far along each task is.
What is the critical path?
The longest chain of dependent tasks from start to finish. It sets the minimum project duration, and any delay on it delays the whole project. Tasks off the critical path have slack and can slip without moving the end date.
What is the difference between a Gantt chart and a timeline?
A timeline shows key dates and milestones. A Gantt chart shows every task as a bar with its duration and dependencies. A timeline is a Gantt chart with the task rows removed.
Do I need software to make a Gantt chart?
No. A spreadsheet with shaded cells is a Gantt chart, and it is the right tool for most improvement projects. Software becomes worth it when dependencies and resource conflicts are too many to manage by hand.
Who invented the Gantt chart?
Henry Gantt, around 1910 to 1915, for production and wartime scheduling. Karol Adamiecki had drawn similar charts in 1896, but Gantt's version is the one that spread and took his name.
Related tools
The Gantt chart is the schedule view of a project plan; the rest of the plan is covered under project timelines, resource management, cost-benefit analysis, stakeholder engagement, and scope creep. For the general project management reference, see the Association for Project Management's Gantt chart resource. The projects most often charted this way are on the kaizen, 5S, and floor marking pages.