Hardware resources for VDI

It depends on what they run. I have one customer who has a RDSH server for 20 people. It has 2 vCPU's and uses up to 12 gigs of ram during peak usage. I have another client with 10 users who are happy with 1 vCPU and 3 gigs. I then have another customer with 2 servers with 4 vCPU's and 7 gigs each serving approx 20 users per server.