This article will help you to calculate the expected free space on vSAN datastore if we disable the deduplication and compression on an existing vSAN cluster.
VMware vSAN 7.x
VMware vSAN 8.x
Verify the vSAN capacity details from vCenter by navigating to vSAN Cluster > Monitor > vSAN > Capacity tab.What if analysis in this page shows the effective free space without Deduplication and compression based on the policy selected.