The statistics below are for those of you using Raspberry Pi stats boxes. For those of you using Meraki's, you can access your statistics (in real time and always up to date) here.
Within the Meraki dashboard, under the Network-Wide category to the left, click on 'Summary Report.' Near the top of the page, to the right of the Summary Report heading, there is a drop-down list where you can select a date range, or just the last week or month. Choose the range you want to see and click on the Update button.
The page will now display the statistics for the last month. The most useful number is probably the number of clients under SSID #1, in the Top SSIDs by usage category. You'll see roughly the same number in the Clients section, along with a Daily Average of clients.
If you look at the top right portion of the page, you'll see an "Email this Report" button and a "Schedule Report Email" button. I recommend you use the "Schedule" button to have the Meraki send you a monthly report. You can have it sent to more than one email address as well.
For more in-depth statistics, look under Organization on the left side of the dashboard, and choose "Location Analytics".