This can be retrieved programmatically via the Atlas API.
https://www.mongodb.com/docs/atlas/reference/api-resources-spec/v2/#tag/Monitoring-and-Logs/operation/getDiskMeasurements
# Fetch Free Space for Data partition for one process
curl -s -u 'API_PUBLIC_KEY:API_PRIVATE_KEY' \
-H "Accept: application/vnd.atlas.2025-02-19+json" \
--digest "https://cloud.mongodb.com/api/atlas/v2/groups/588fc162d383ad09d65f7ae2/processes/atlas-wg5ldy-shard-00-00.9qfvh.mongodb.net:27017/disks/data/measurements?granularity=PT5M&period=PT5M&m=DISK_PARTITION_SPACE_PERCENT_FREE" | jq '.measurements'
[
{
"dataPoints": [
{
"timestamp": "2025-02-26T01:39:20Z",
"value": 79.26505344784972
}
],
"name": "DISK_PARTITION_SPACE_PERCENT_FREE",
"units": "PERCENT"
}
]