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<?php

function number_longhand( $num ) {
	$is_array = is_array( $num );

	if( !$is_array )
		$num = array( $num );

	$num = preg_replace( '/[^\d\.BMK]/i', '', $num );
	foreach( $num as $index => $n ) {
		switch( $n[strlen($n) - 1] ) {

			case 'B':
			case 'b':
				$n *= 1000000000;
			break;

			case 'M':
			case 'm':
				$n *= 1000000;
			break;

			case 'K':
			case 'k':
				$n *= 1000;
			break;

		}
		$num[$index] = $n;
	}

	if( !$is_array )
		return $num[0];
	else
		return $num;

}

$numbers = array(
	'1m',
	'.5m',
	'254 k',
	'1.2 M',
	'1,200',
	'1500',
	'0',
	'1.5',
);

foreach( $numbers as $n ) {
	$f = number_longhand( $n );
	printf( "%s = %s = %s<br>", $n, $f, number_format( $f, 2 ) );
}

echo '<hr>';

var_dump( number_longhand( $numbers ) );