Measure string size in Bytes in php

05/15/2020 12:30:01

I am doing a real estate feed for a portal and it is telling me the max length of a string should be 20,000 bytes (20kb), but I have never run across this before.

How can I measure byte size of a varchar string. So I can then do a while loop to trim it down.

Verified Answer (29 Votes)

09/27/2011 17:19:38

You have to figure out if the string is ascii encoded or encoded with a multi-byte format.

In the former case, you can just use strlen.

In the latter case you need to find the number of bytes per character.

the strlen documentation gives an example of how to do it :


Answer #2 (68 Votes)

03/15/2012 15:55:43

You can use mb_strlen() to get the byte length using a encoding that only have byte-characters, without worring about multibyte or singlebyte strings. For example, as drake127 saids in a comment of mb_strlen, you can use '8bit' encoding:

    $string = 'Cién cañones por banda';
    echo mb_strlen($string, '8bit');

You can have problems using strlen function since php have an option to overload strlen to actually call mb_strlen. See more info about it in

For trim the string by byte length without split in middle of a multibyte character you can use:

mb_strcut(string $str, int $start [, int $length [, string $encoding ]] )

Answer #3 (25 Votes)

09/27/2011 17:19:18

Do you mean byte size or string length?

Byte size is measured with strlen(), whereas string length is queried using mb_strlen(). You can use substr() to trim a string to X bytes (note that this will break the string if it has a multi-byte encoding - as pointed out by Darhazer in the comments) and mb_substr() to trim it to X characters in the encoding of the string.

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