Old question - but I recently needed this along with the row count... here is a query for both - sorted by row count desc:
SELECT t.owner,
t.table_name,
t.num_rows,
Count(*)
FROM all_tables t
LEFT JOIN all_tab_columns c
ON t.table_name = c.table_name
WHERE num_rows IS NOT NULL
GROUP BY t.owner,
t.table_name,
t.num_rows
ORDER BY t.num_rows DESC;
Maybe something like this:
SELECT count(*) FROM user_tab_columns WHERE table_name = 'FOO'
this will count number of columns in a the table FOO
You can also just
select count(*) from all_tab_columns where owner='BAR' and table_name='FOO';
where the owner is schema and note that Table Names are upper case
Source: Stackoverflow.com