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  • I know this is an older post but I was trying to do something similar this evening and had to figure it out myself, so I thought I’d share what I did. Hopefully it can help someone else, but apologies in advance for the lack of brevity.

    Before I go any further, I also want to clarify that this is a PARTIAL reply since it only addresses the OP’s primary question… “how do I find the block ID of a particular block in a specified post?” It’s important to note that get_field('contact_block', 'block_5c8b98f36c5c7'); is NOT valid ACF code and will NOT return ACF data from a specified block ID.

    Down to business.

    What I did was utilize the parse_blocks() function in order to return an object of blocks from a particular other post. The function takes the CONTENT of a page to parse, so I did this in one line like so.

    $post_blocks = parse_blocks( get_the_content( '', false, 166 ) );

    From there you can loop through the object and look at the information you have about each block. You can quickly short-circuit based on blocks that aren’t of the type you care about, or you can look at any other information about them. For example, I made an “intro-content” block and created a single ACF field of “color” which is a simple colorpicker.

    foreach ( $post_blocks as $block ) {
        if ( 'acf/intro-content' != $block['blockName'] ) {
            continue;   // Skip this block if it's not the right block type
        if ( isset( $block['attrs']['id'] ) ) {
            $my_block_id = $block['attrs']['id'];
            break;  // Found a hit, get out of the loop

    This is what the individual block object looked like according to a var_dump(), to show what WordPress knows about that block and how/why I targeted things the way I did.

    array (size=5)
      'blockName' => string 'acf/intro-content' (length=17)
      'attrs' => 
        array (size=5)
          'id' => string 'block_5fb5d249c67e8' (length=19)
          'name' => string 'acf/intro-content' (length=17)
          'data' => 
            array (size=2)
              'color' => string '#1800d3' (length=7)
              '_color' => string 'field_5fb5d169b6174' (length=19)
          'align' => string '' (length=0)
          'mode' => string 'edit' (length=4)
      'innerBlocks' => 
        array (size=0)
      'innerHTML' => string '' (length=0)
      'innerContent' => 
        array (size=0)

    Putting it all together, this was a quick function that I wrote for getting back an array of block IDs which I could filter based on block type. It also lets you choose how many you want back (so you can tell it to stop after the first one, if you wanted).

    function custom_get_acf_block_ids_from_post( $post_id, $return_count = -1, $arr_block_types = array() ) {
        // If the post object doesn't even have any blocks, abort early and return an empty array
        if ( ! has_blocks( $post_id ) ) {
            return array();
        // If $arr_block_types is not an array, add the param as the only element of an array. This lets us pass a string if we wanted
        if ( ! is_array( $arr_block_types ) ) {
    	    $arr_block_types = array( $arr_block_types );
        // Only check the size of $arr_block_types once. Set a boolean so we know if we're filtering by block type or not
        $filter_block_types = ( 0 == count( $arr_block_types ) ) ? false : true;
        // Get our blocks from the post content of the post we're interested in
        $post_blocks = parse_blocks( get_the_content( '', false, $post_id ) );
        // Initialize some vars before we get into the loop
        $arr_return = array();
        $found_count = 0;
        // Loop through all the blocks
        foreach ( $post_blocks as $block ) {
            // Skip this item in the loop if the current block isn't one of the block types we're interested in
            if ( $filter_block_types && ! in_array( $block['blockName'], $arr_block_types ) ) {
            // Confirm the block we're looking at has an ID to return in the first place
            if ( isset( $block['attrs']['id'] ) ) {
                // Add this block ID to the return array
                $arr_return[] = $block['attrs']['id'];
                // Increment our found count, and see if we've found as many results as we wanted. Return early if so
                    if ( $found_count == $return_count ) {
                        return $arr_return;
        // If we made it all the way here, return whatever we've found
        return $arr_return;

    Which in my case, gave me back an array with just a single result based on the page I was looking at.

    array (size=1)
      0 => string 'block_5fb5d249c67e8' (length=19)

    So there you go! How to find block ID’s from a specified post/page ID.