get hours difference between two dates in php

$hourdiff = round((strtotime($time1) - strtotime($time2))/3600, 1);

//get Date diff as intervals 
$d1 = new DateTime("2018-01-10 00:00:00");
$d2 = new DateTime("2019-05-18 01:23:45");
$interval = $d1->diff($d2);
$diffInSeconds = $interval->s; //45
$diffInMinutes = $interval->i; //23
$diffInHours   = $interval->h; //8
$diffInDays    = $interval->d; //21
$diffInMonths  = $interval->m; //4
$diffInYears   = $interval->y; //1

//or get Date difference as total difference
$d1 = strtotime("2018-01-10 00:00:00");
$d2 = strtotime("2019-05-18 01:23:45");
$totalSecondsDiff = abs($d1-$d2); //42600225
$totalMinutesDiff = $totalSecondsDiff/60; //710003.75
$totalHoursDiff   = $totalSecondsDiff/60/60;//11833.39
$totalDaysDiff    = $totalSecondsDiff/60/60/24; //493.05
$totalMonthsDiff  = $totalSecondsDiff/60/60/24/30; //16.43
$totalYearsDiff   = $totalSecondsDiff/60/60/24/365; //1.35

$date1 = "2007-03-24";
$date2 = "2009-06-26";

$diff = abs(strtotime($date2) - strtotime($date1));

$years = floor($diff / (365*60*60*24));
$months = floor(($diff - $years * 365*60*60*24) / (30*60*60*24));
$days = floor(($diff - $years * 365*60*60*24 - $months*30*60*60*24)/ (60*60*24));

printf("%d years, %d months, %d days\n", $years, $months, $days);

$from_date ='01-01-2013';
$to_date ='05-01-2013';

$from_date = new DateTime($from_date);
$to_date = new DateTime($to_date);

for ($date = $from_date; $date <= $to_date; $date->modify('+1 day')) {
  echo $date->format('l') . "\n";
}

<?php
function dateDifference($start_date, $end_date)
{
    // calulating the difference in timestamps 
    $diff = strtotime($start_date) - strtotime($end_date);
     
    // 1 day = 24 hours 
    // 24 * 60 * 60 = 86400 seconds
    return ceil(abs($diff / 86400));
}
 
// start date 
$start_date = "2016-01-02";
 
// end date 
$end_date = "2016-01-21";
 
// call dateDifference() function to find the number of days between two dates
$dateDiff = dateDifference($start_date, $end_date);
 
echo "Difference between two dates: " . $dateDiff . " Days ";
?>