Adding grid lines to Microsoft Excel charts helps to recognize data values by making it easier to line up points on the graph with the bottom left side of the scale. Major grid lines are bolder lines that distinguish scale milestones, such as increments of 5 or 100, depending on the scale of your chart. Minor grid lines fill in the gaps with lighter lines and represent smaller units, such as increments of 1. Excel allows you to add major and minor grid lines simultaneously, which may be vertical, horizontal or both.
Open your spreadsheet chart in Microsoft Excel.
Click the chart to enable the Chart Tools at the top of the window.
Click "Layout" tab in the Chart Tools menu group.
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Click "Gridlines" from the Axes group. Point to either "Primary Horizontal Gridlines" or "Primary Vertical Gridlines" and click "Major & Minor Gridlines" to add either horizontal or vertical lines, respectively. To add vertical and horizontal grid lines, perform the procedure for both axes.