---
title: Gantt chart
lang: en
type: tuto
phases:
  - specification
tags:
  - proj
  - tuto
  - planification
prerequis:
  - retroplanning-en
  - wbs-en
aa:
  - RA-PROJET-C07-1/PROJ/2
draft: false
source_fr: conduite/proj/gantt.md
source_sha256: c7f6d4d657d5df75e7d2e7afa20ad384a1a810e6c1d7cd4d7d4eb7f94976d92f
---

The **Gantt chart** (or Gantt diagram) is the graphical tool that gives shape to a [[retroplanning-en|backward plan]]: tasks in rows, calendar in columns, horizontal bars showing durations and overlaps. Its teaching strength is that it brings out visually the **dependencies** between tasks and the **bottlenecks** where several tasks overlap dangerously.

![Gantt chart — generic mini-diagram: 4 tasks, 8 weeks, milestones and a dependency](/ressources/img/gantt/generique.svg)

## What is it for?

The Gantt chart makes the time sequence of a project visible at a glance. Where a [[wbs-en|WBS]] says *what* and a [[retroplanning-en|backward plan]] says *when*, the Gantt chart **lays one over the other** on a single graphical support. That is what lets you see rather than read.

Three roles:

- **Making the critical dependencies visible** between tasks — this task blocked by that one, this delivery gating the start of the next. The dependency arrows are what tells a Gantt chart apart from a plain list dropped onto a timeline.
- **Spotting the calendar bottlenecks** where several tasks overlap dangerously. If three critical tasks land in the same week, you see it before the week arrives.
- **Acting as a communication support in review.** Milestones and tasks can be read by an outside reader (supervisor, client) with no prior context, useful as soon as the state of the project has to be presented.

## How do you build one?

Five steps:

1. **Take the task list from the [[wbs-en|WBS]]** and their estimated durations.
2. **Put the [[jalons-en|milestones]] on the time axis in columns** as fixed points.
3. **Draw one horizontal bar per task** between its start date and its end date.
4. **Add the dependencies** as arrows linking the tasks that necessarily follow one another.
5. **Update at every phase review**. Without that, the Gantt chart lies from the first slip onwards.

On the tooling side, three main options are available: **Excel or paper** (quick to set up, enough for a simple Gantt chart), **GanttProject** (dedicated free software, handles dependencies cleanly), **Trello** (kanban task tracking, a useful complement to the Gantt chart but not a replacement for it: the continuous time dimension is lost). Choose one tool and stick to it. Scattering the planning across three unsynchronised supports is worse than one imperfect tool.

*A worked case: the Gantt chart of a connected weather station project over 15 weeks.*

![Gantt chart of a connected weather station project](/ressources/img/gantt/station-meteo.svg)

## Pitfalls

**A Gantt chart frozen once produced.** A Gantt chart drawn at the start of a phase and never reopened lies from the first slip onwards. Conversely, a Gantt chart updated every week, however imperfect, becomes a powerful steering tool: it reveals the slips early, while there is still room to act.

**Too fine-grained.** A day-by-day Gantt chart on a project running several months becomes unreadable and demoralising. Every delay of a few days shows up as a crisis. Weekly granularity is enough on a school project.

**No visible dependencies.** A Gantt chart with no dependency arrows is just a list of tasks dropped onto a timeline. The teaching value lies precisely in showing **who blocks whom**. A delay on the PCB order can push three integration tasks back.

## See also

- [[specification-technique-en|Technical specification]] — step 5, where the project Gantt chart is built
- [[retroplanning-en|Backward planning]] — the time plan the Gantt chart gives shape to
- [[wbs-en|WBS]] — the work breakdown whose leaves become the bars of the Gantt chart
- [[jalons-en|Milestones]] — fixed points put on the Gantt chart before the tasks
- [[gestion-de-projet-en|Project planning and tracking]] — the cross-cutting thread that keeps the Gantt chart alive