Select a count of record sharing the same value than record X

Figure a table with two columns: id, catId

How to select the records having the same catId than the record having id = 3?

Example:

id catId
1   3
2   4
3   4
4   4
5   3

1. Input: 3

2. Then catId of {id = 3} is 4

3. Then count of records having {catId = 4} is 3

4. Output: 3 records

SELECT COUNT(*)
FROM table t1
JOIN table t2 USING (catId)
WHERE t1.id = 3

SELECT COUNT(DISTINCT t2.id)
FROM table t1
JOIN table t2 USING (catId)
WHERE t1.id = 3