59 GB a month
With a 50% safety margin for traffic spikes, look for at least 88 GB. Browser caching usually lowers the real figure, so this is a cautious estimate.
How it works
Visits × pages per visit × page size gives the monthly transfer, and we divide by 1,024 to turn megabytes into gigabytes. Your analytics tool shows visits and pages per visit, and your browser's network panel shows page size.