how do i add 1 to a found css value

how do i add 1 to a found css value

i've got a div and i'm setting its height to the height of an image like so:

$('#gallery').css({height: $('#gallery a').find('img').css('height')});

how would i add 1px to this?

lets say the image is 300px, how do i set the height of my gallery div to 301px?

thanks