Polygon measurement displays incorrect values when using the Measure tool in a different ArcGIS Pro project

Description

When measuring the length or area of a polygon in a different project using the Measure tool, the measurement displays an incorrect value in ArcGIS Pro.

The following are examples of a polygon area measurement using the Measure tool in different ArcGIS Pro projects. In the first image, the measurement of the polygon area is 8,207.77 sqKm, but in a different project (the second image), the measurement of the polygon area is 8,160.72 sqKm.

Cause

Known causes of the problem include:

• The coordinate system of the map frame is different from the feature layer.
• The Measure tool uses a different measurement mode in different projects.

Solution or Workaround

Depending on the cause, use one of the methods below to resolve the issue.

Change the coordinate system of the map frame

In ArcGIS Pro, change the coordinate system of the map frame so it is similar to the feature layer. Refer to ArcGIS Pro: Specify the coordinate systems of maps and scenes for steps to do this.

Note: 
To check the coordinate system of the feature layer, refer to the Tip section in ArcGIS Pro: Specify a coordinate system.

Use the same measurement mode for the Measure tool in a different project

In ArcGIS Pro, change the measurement mode for the Measure tool so it is similar to the previous project. Use the Planar mode to measure the area or length of a polygon. Refer to ArcGIS Pro: Measurement modes for more information.

The image below shows the Measure tool displaying the correct measurement value for the polygon area in ArcGIS Pro.