Quick way to get the number of days in a month with PHP

I’m building a php calendar and need to know the total number of days in a month in the past I've used: 

echo cal_days_in_month(CAL_GREGORIAN, 2, 2017);

For the current month you can use:

echo date('t');

Or for a more a date based approach:

echo date('t', strtotime('2017-02-01'));