I have weight data stored in a SQL Server table as varchar data type.  Generally the data is stored like '57.25 kg'.  I am trying to extract the 57.25. 

This is what I have at the moment:

select convert(numeric, (rtrim(STR(weight,1,(charindex('  ',weight)))))) from ahi_patient
where weight is not null
and weight <> 0

I am getting the following error:

Syntax error converting the varchar value '79.38 kg' to a column of data type int.

Any suggestions on how to get past this?

thanks