O comando a seguir é específico para clusters do Atlas Flex, clusters gratuitos e instâncias sem servidor (obsoleto):
atlasSize
Retorna o tamanho cumulativo em todos os bancos de dados para as seguintes estatísticas do banco de dados de dados:
{   "totals": {   "collections": [number-total-collections],   "views": [number-total-views],   "objects": [number-total-objects],   "avgObjSize": [number-average-across-all],   "dataSize": [number-total-dataSize],   "storageSize": [number-total-storageSize],   "numExtents": [number-total-numExtents],   "indexes": [number-total-indexes],   "indexSize": [number-total-indexSize],   "fileSize": [number-total-fileSize],   "numDatabases": [number-total-databases],   "indexSize": [number-total-indexSize] },   "atlasSize": [number-total-data-plus-total-index-size],   "ok": 1 } 
O campo atlasSize representa a combinação do tamanho total de dados e índices no cluster.
Exemplo de solicitação
db.runCommand({atlasSize:1}) 
Exemplo de resposta
{       "totals" : {         "collections" : 11,         "views" : 0,         "objects" : NumberLong(530025),         "avgObjSize" : 277.0923742138365,         "dataSize" : NumberLong(532890980),         "storageSize" : NumberLong(555319296),         "numExtents" : NumberLong(0),         "indexes" : 11,         "indexSize" : NumberLong(4792320),         "fileSize" : NumberLong(0),         "numDatabases" : 4       },       "atlasSize" : NumberLong(537683300),       "ok" : 1 }