Chunks not splitting on MongoDB sharded clusters

I have created 2 shard servers named rs1 and rs2. Now in the database collection there are multiple records those should split on these 2 servers in chunks. The sharding key is TxnMonth. It is not unique. Now I have given the chunk size as 1 MB. When I inserted records corresponding to "TxnMonth" : 1, "TxnMonth" : 2 and "TxnMonth" : 3, the data was splitted onto 2 shards where on rs1 there were 2 chunks and on rs2 there was 1 chunk. On checking, data for TxnMonth : 1 and 2 was on rs1 and data for TxnMonth : 3 was on rs2. On running, sh.status(), it gave this output- { "_id" : "shardPOC", "primary" : "rs1", "partitioned" : true } shardPOC.machines shard key: { "TxnMonth" : 1 } unique: false balancing: true chunks: rs1 2 rs2 1 { "TxnMonth" : { "$minKey" : 1 } } -->> { "TxnMonth" : 1 } on : rs1 Timestamp(2, 1) { "TxnMonth" : 1 } -->> { "TxnMonth" : 3 } on : rs1 Timestamp(1, 2) { "TxnMonth" : 3 } -->> { "TxnMonth" : { "$maxKey" : 1 } } on : rs2 Timestamp(2, 0) { "_id" : "NewTestDB", "primary" : "rs1", "partitioned" : false } After this, I started inserting records for TxnMonth : 4, 5, 6, 7 and 8, to check when the chunk on rs2 will split but even if the chunk size exceeded 1 MB size, it didn't split. Below is the output of db.collection.getShardDistribution() - Shard rs1 at rs1/JCB-DB1:27012 data : 57KiB docs : 80 chunks : 2 estimated data per chunk : 28KiB estimated docs per chunk : 40 Shard rs2 at rs2/JCB-DB1:27013 data : 1.1MiB docs : 1560 chunks : 1 estimated data per chunk : 1.1MiB estimated docs per chunk : 1560 Totals data : 1.15MiB docs : 1640 chunks : 3 Shard rs1 contains 4.87% data, 4.87% docs in cluster, avg obj size on shard : 740B Shard rs2 contains 95.12% data, 95.12% docs in cluster, avg obj size on shard : 740B What I expected was that the chunk will split after it exceeds 1 MB but it did not. Can someone explain the reason? Thanks in advance.