const
  KFactor = 1024;

function SizeBytesToMB(Value: Extended; MbLabl: String; Offset: Integer): String;
begin
  MbLabl := Trim(MbLabl);
  if MbLabl <> '' then
    MbLabl := ' ' + MbLabl;
  Result := FloatToStr(Value / (KFactor * KFactor));
  if Offset = 0 then
    Result := Copy(Result, 0, Pos('.', Result) - 1) + MbLabl
  else
    Result := Copy(Result, 0, Pos('.', Result) + Offset) + MbLabl;
end;

Caption:=ExpandConstant('{cm:needsize1} '+SizeBytesToMB({#SizeAfterWorkInBytes}, '', 0));+' {cm:needsize2}');