Gantt Chart
A timeline of bars that shows when each activity starts, how long it runs, and when it ends.
Quick Answer
A Gantt chart is a schedule displayed as horizontal bars on a calendar timeline, one bar per activity. Bar length shows duration, position shows start and finish dates, and arrows can show dependencies. It is the most common way construction schedules are communicated because anyone on the job can read it at a glance.
The Full Picture
Gantt charts exist because a list of activities and dates is hard to read, and a network diagram is harder still for most people on a project. Plotting each activity as a bar against a calendar turns the schedule into a picture: what happens when, what overlaps, and where the project ends. The format dates back to Henry Gantt's work in the 1910s and remains the default output of nearly every scheduling tool.
Mechanically, each row is an activity or summary group, the horizontal axis is time, and each bar spans the activity's start and finish. Modern charts overlay more information: dependency arrows, milestones as diamonds, the critical path highlighted in red, percent complete as a filled portion of the bar, and a baseline bar underneath to show slippage.
In practice, a GC's schedule is usually built as a CPM network in a tool like Primavera P6 or Microsoft Project, then printed or shared as a Gantt chart. The owner sees a one-page summary Gantt, the superintendent sees a detailed look-ahead Gantt filtered to the next few weeks, and subcontractors see the bars for their trade.
In preconstruction, the Gantt chart is how the team communicates the proposed sequence and duration to the owner during pursuit and GMP development. A clear summary Gantt showing design milestones, permits, long-lead procurement, and major construction phases is often part of the proposal. The failure mode is a chart drawn by hand with no logic behind it, which looks credible but cannot recalculate when a date moves.
Real Examples
Common Misconceptions
People assume: A Gantt chart and a CPM schedule are the same thing.
Actually: A Gantt chart is a display format. A CPM schedule is a logic network of activities, durations, and dependencies that calculates dates and the critical path. A CPM schedule is usually shown as a Gantt chart, but a Gantt chart drawn without logic ties is just a picture that will not update when something changes.
People assume: If the bars look reasonable, the schedule is sound.
Actually: Visual plausibility says nothing about missing logic, hard-coded date constraints, or excessive float. Schedule quality checks such as the GAO and DCMA assessments look at the underlying network, not the bars.
Frequently Asked Questions
What is a Gantt chart used for in construction?
It communicates the project schedule visually: when each activity starts and finishes, which activities overlap, where milestones fall, and how the project is tracking against the baseline. Owners, superintendents, and subcontractors all use Gantt views filtered to their needs.
What is the difference between a Gantt chart and a CPM schedule?
CPM is the scheduling method that links activities with dependencies and calculates dates and the critical path. A Gantt chart is one way to display the result. Most construction schedules are CPM networks shown as Gantt charts.
What software makes construction Gantt charts?
Primavera P6 and Microsoft Project are the most common for CPM-based Gantt charts on commercial work. Many project management platforms and spreadsheets can also produce simple Gantt views, though usually without full CPM logic.
What are the limitations of a Gantt chart?
On large projects with thousands of activities, a Gantt chart becomes hard to read, and it does not clearly show why an activity is late. Dependencies and float are easier to analyze in the underlying CPM data than in the bars.