The NF variable is set to the total number of fields in the input record. So:
echo "a b c d" | awk --field-separator=" " "{ print NF }"
will display
4
Note, however, that:
echo -e "a b c d\na b" | awk --field-separator=" " "{ print NF }"
will display:
4 2
Hope this helps, and happy awking