how to cut column that is not equally spaced by delimeters

hi friends,
when i run this command on my machine;

df -k /export/home
output of this command i gets as:

/Filesystem kbytes used avail capacity Mounted on
/dev/dsk/c0t1d0s7 5043168 4520584 472153 91% /export/home

i want to use column avail from above output: i was trying cut command as
: df -k /export/home |grep -v Filesystem|cut -d" " -f8

but am not getting desired result:i mean somemachine i get this avail column value:472153(that i want) but somemachine i get a blank and if i use at that machine
df -k /export/home |grep -v Filesystem|cut -d" " -f7 then desired result i got..
but i need a general solution that can work at all machine ..
what i am feeling thhat output of df -k command is not equally spaced so that i am not able to properly cut that avail column value..

could you people give me some idea .. so that i can cut avail field by matching it's name

try this:

df -k | grep -v Filesystem | awk '{print $4}'