Add Get Size Stats For A Collection as a mongodb til

mongodb/get-size-stats-for-a-collection.md

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+# Get Size Stats For A Collection
+
+For any collection in your MongoDB instance.
+
+```javascript
+> db.getCollectionNames()
+["books", "authors", "genres"]
+```
+
+You can list a collection of stats, which include the amount of disk space that
+collection is utilizing.
+
+```javascript
+> db.books.stats().size
+11057056
+```
+
+By default this size is in bytes, which isn't all that human-readable of a
+value.
+
+By passing in a `scale` value to `stats()`, you can get a value that is a bit
+more understandable. A scale of `1024` would give you kilobytes, so a scale of
+`1024 * 1024` would give you megabytes.
+
+```javascript
+> db.books.stats({ scale: 1024 * 1024 }).size
+10
+```
+
+[source](https://docs.mongodb.com/manual/reference/method/db.collection.stats/)