no, length + GIRTH. So basically length + (2x height) + (2x width)
Also keep in mind that you need to properly protect it with bubble wrap etc. The packaged frame may well be 2" longer, wider and taller after that.
What I did to further protect mine, was to take a broom handle, cut it down and put it between the rear dropouts.
That way, even if they would put it on its side and place a big box on top of it, the rear end couldn't be bent during transport.
I did the same thing on the other end as well, even if the fork was removed from the frame and put in the box sideways.
I also duct taped pieces of wood and broom handle into the box for further strengthening.
The extra bit of weight doesn't really make a difference, but it may very well protect the frame if the people at USPS, Royal mail or the airport are a bit careless.
It's a long trip, so lots of opportunities to get damage if you don't do your homework.