Thanks, but now I'm getting a different error : -

Msg 8115, Level 16, State 2, Line 5

Arithmetic overflow error converting expression to data type float.

my actual query is : -

declare @radius decimal(18,2)

DECLARE @radians float

SELECT @radians = 57.295779513082323 --> 180/PI

SELECT @radius=5

;with cteDistCalc

as(

SELECT t1.*,

DistanceInMiles = 3963.0*acos(sin(t1.Latitude/(@radians)) * sin(t2.Latitude/(57.295779513082323))

+ cos(t1.Latitude/(@radians)) * cos(t2.Latitude/(@radians)) * cos(t2.Longitude/(@radians) - t1.Longitude/(@radians)))

FROM dbo.postcodes t1

JOIN dbo.postcodes t2

on t1.Latitude between t2.Latitude - @radius and t2.Latitude + @radius

and t1.Longitude between t2.Longitude - @radius and t2.Longitude + @radius

where t1.postcode='SM4 6DX'

)

select * from cteDistCalc WHERE DistanceInMiles < @radius

ORDER BY DistanceInMiles

[/code}