The other day I had to iterate over a large number of items but to avoid a timeout I could only compute a certain amount at a time. So I had to split the number into equal chunks and a remainder. Here’s an easy way to determine the chunk size:

$totalNumber = 50321;
$chunkSize = 1023;

$remainder =  $totalNumber % $chunkSize;
$chunks = ($totalNumber - $remainder) / $chunkSize;

The code return the following values:
$remainder => 194
$chunks => 49
Verification: (49 * 1023) + 194 = 50321

How does it work?
In line 4 $totalNumber is divided by a modulo operator (“%” is the PHP token for modulo). The operator returns the remainder of the division (194 in this case). By subtracting this value from $totalNumber it becomes a whole number multiple of $chunks and the division with $chunkSize equals the desired number of $chunks (line 6).
Now you have the number of necessary iterations and the remaining part.