Converts a number into a short version, eg: 1000 -> 1k

short-version-number.php

<?php

// Converts a number into a short version, eg: 1000 -> 1k
function thousandsCurrencyFormat( $num ) {

	if ( $num > 999 ) {

		$x               = round( $num );
		$x_number_format = number_format( $x );
		$x_array         = explode( ',', $x_number_format );
		$x_parts         = array( 'k', 'm', 'b', 't' );
		$x_count_parts   = count( $x_array ) - 1;
		$x_display       = $x;
		$x_display       = $x_array[0] . ( (int) $x_array[1][0] !== 0 ? '.' . $x_array[1][0] : '' );
		$x_display      .= $x_parts[ $x_count_parts - 1 ];

		return $x_display;
	}

	return $num;
}