How many gb is 23 MB

I assume you are asking about computer storage 'Megabytes' and 'Gigabytes'.
The general correct way to present these terms in shorthand is as MB and GB, the use of a small 'b' indicates 'bits' rather than Bytes. the use of small 'm' is usually taken as 'milli' (one thousandth part), but this does not apply to bits and bytes.

1 MB = 1024 KB
1 GB = 1024 MB

Thus 23 MB is 0.0224609375 GB