How does the MigrationWiz Assessment tool work?

The MigrationWiz Assessment tool is available for migration projects for the following scenarios:

Mailbox migration project, with G Suite as the Source. The Destination can be any supported Destination type.
Document migration project, with Google Drive as the Source. The Destination can be any supported Destination type.
Performing an assessment before a Google Mail or Google Drive migration is highly recommended to estimate the number of required licenses because:

In Google Mail migrations, email messages may have been assigned several labels. When migrating to Office 365, multi-labeled email messages result in a separate copy under each corresponding Exchange folder, which increases the storage consumption.
In Google Drive migrations, Google Docs, Sheets, Slides, Drawings, etc., do NOT count toward your storage limit. In OneDrive for Business, everything consumes space regardless of the file type. Google documents are converted to their equivalent Microsoft Office document types during the migration, so the space required in OneDrive for Business can be higher than in Google Drive.
Note: The assessment tool will scan each mailbox and determine the total size of the mailbox and the count of the folders in the mailbox. This is what will be included in the assessment report. It does not provide information on the number of items (i.e., Mail, Contact and Calendar). Please refer to the section below for more information on how to read the assessment report.

Here is how to use the MigrationWiz Assessment tool:

Create the MigrationWiz project, either mailbox or document migration project, depending upon your Source requirements.
Enable Oauth2.0 authentication. For guidance, see Enable access to G Suite using OAuth 2.0.
Notes:
When setting up your MigrationWiz project, it is very important to checkmark the box labeled Use Administrator Login, and enter the customer domain name, under the Your Domains field.
Important: If you do not do this step, then an email will be sent to all users, requesting their credentials, as part of the assessment.
If this step is completed, then users will not receive an email as part of the assessment, which is the strongly recommended approach to follow.
G Suite mailbox migration projects require the BitTitan client ID to be granted access to the scopes included in the Knowledge Base article referenced above (and here: Enable access to G Suite using OAuth 2.0).
Google Drive document migration projects require the BitTitan client ID to be granted access to the scopes included in the Knowledge Base article referenced above, plus API access needs to be enabled.
Add Users.
Note: ​In order to run an assessment, the specified Destination mailboxes and/or OneDrive for Business accounts must be fully provisioned. If the Office 365 licenses cannot be assigned to all the Users at that stage of the migration, at least one (1) license needs to be assigned to a single User. The email address for that single User must be specified for all Destination email addresses in the Users.csv to be imported into the MigrationWiz project, with the Office 365 global admin credentials enabled. When it is time start the migration, all Destination email addresses can be bulk edited by running a script (follow the directions in KB005157), or by deleting and reimporting the Users.csv file with the correct Destination email addresses.
Select the Users that need assessment.
Note: You can select All Users, as indicated in the screenshot below:
check mark.png
Click on Start.
From the drop-down list, select Assessment.
Select the items to be included in the assessment.
Click on the Start Assessment button.
Once complete, the status will change to "Assessment Complete", as in this screenshot:
assessment complete.png
Now click on the Up arrow at the top of the MigrationWiz dashboard to return to the top level. This will show the list of MigrationWiz projects.
up arrow 1.png
From this level, click on the pie chart:
pie_chart.png
Click OK to receive an email with the project statistics.
The sender of this email will be: [e-mail] and the subject header will be: Migration Statistics for Project: "your project name".
This email will contain three (3) .zip file attachments. Unzip the attachment with the name: ProjectStats.zip.
Once unzipped, open the file named ProjectStats.csv.
The total size of the mailbox and the count of the folders are reflected in the columns labeled "Mailbox Size (bytes)" and "Folder Count" respectively. Note: The column is labeled "Mailbox Size (bytes)" even if the project is a project type other than a Mailbox migration.
You can ignore the other columns which are only populated after the project items have migrated.
Convert this number to GB by dividing this number by 1024*1024*1024.
Now you can calculate the number of licenses per user.
For specifics on license options, see Migration License Types
Notes:

The size calculations may be different from those that are reported in the Google Admin portal. Some possible reasons for this are:

The MigrationWiz Assessment tool will index the entire Source data, and then convert it to the Destination format. The size calculations will be based on the converted data.
If migrating from G Suite to Office 365, and converting labels to folders (which is the default, and recommended selection), then the size calculation will take into account the fact that labels need to be converted to folders on Office 365. This can result in an increase in size for the mailbox, at the Destination.
If migrating from Google Drive to Microsoft OneDrive for Business, then the size calculation will be based on the converted sizes for each document.
If you have date filters under the MigrationWiz project Advanced Options, then the MigrationWiz assessment will take this into account, too. This means that if you have a date filter to migrate just the last 30 days of data, then the assessment will be calculating how much data is in the Source Google Drive accounts for ONLY the last 30 days.
GoogleDrive admin portal is reporting on all data for the user. This includes data in their My Drive and the Shared With Me folder. MigrationWiz assessment is based on what will be migrated because MigrationWiz will only migrate what is in the My Drive.
If you want to migrate data in the "Shared With Me" folder too, then the following steps are required:
Instruct Users to go into the Shared With Me folder and redirect everything into their own My Drive (they will need to right-click on each folder and then select Add To My Drive). Note: This does not move the data. It adds a link so that it can be accessed from their My Drive.
Add the Advanced Option DocumentBrowsingMode=Moderate to your MigrationWiz Project Advanced Options, under Support only options. Refer to KB005034 for more information.
Rerun the assessment.
Purchase User Migration Bundle licenses and assign to each user to be migrated. These licenses include both the Mailbox migration and Document migrations.
Migrate.