Extract and reduce measurement units from strings

example.php

<?php

require __DIR__ . '/strtounits.php';

assert(strtometers('25000.23 meters') === 25000.23);
assert(strtometers('3km, 25.5 meters') === 3025.5);

strtounits.php

<?php

/**
 * @param string $str
 * @return array
 */
function strtounits($str)
{
    $locale = localeconv();

    $units = [
        'k' => 'k',
        'km' => 'k',
        'kms' => 'k',
        'kilometer' => 'k',
        'kilometers' => 'k',

        'm' => 'm',
        'ms' => 'm',
        'meter' => 'm',
        'meters' => 'm',

        'c' => 'c',
        'cm' => 'c',
        'cms' => 'c',
        'centimeter' => 'c',
        'centimeters' => 'c',
    ];
    
    $re = '/(?P<value>\d{1,3}(?:' . (empty($locale['thousands_sep']) ? '' : '\\' . $locale['thousands_sep'] . '?') . '\d{3})*(?:\\' . $locale['decimal_point'] . '\d+)?)\s*(?P<unit>' . join ('|', array_keys($units)) . ')/';
    $count = preg_match_all($re, $str, $matches);

    if ($count === 0) {
        return false;
    }

    $result = [];

    for ($i = 0; $i < $count; $i++) {
        $unit = $units[$matches['unit'][$i]];
        $value = str_replace($locale['thousands_sep'], '', $matches['value'][$i]);

        if (!isset($result[$unit])) {
            $result[$unit] = 0;
        }

        $result[$unit] += $value;
    }

    return $result;
}

/**
 * @param string $str
 * @return float
 */
function strtounit($str, array $multipliers)
{
    $units = strtounits($str);

    if ($units === false) {
        return false;
    }

    $result = 0;

    foreach ($units as $unit => $value) {
        if (!isset($multipliers[$unit])) {
            continue;
        }

        $result += $value * $multipliers[$unit];
    }

    return $result;
}

/**
 * @param string $str
 * @return float
 */
function strtokilometers($str)
{
    return strtounit($str, [
        'k' => 1,
        'm' => 0.01,
        'c' => 0.00001,
    ]);
}

/**
 * @param string $str
 * @return float
 */
function strtometers($str)
{
    return strtounit($str, [
        'k' => 1000,
        'm' => 1,
        'c' => 0.01,
    ]);
}

/**
 * @param string $str
 * @return float
 */
function strtocentimeters($str)
{
    return strtounit($str, [
        'k' => 100000,
        'm' => 100,
        'c' => 1,
    ]);
}