How do I calculate distance using Google map apis

Presuming that you are using the Distance Matrix API (and not the Directions API) then the form of a request should be :

https://maps.googleapis.com/maps/api/distancematrix/outputFormat?parameters

And your code should look something like this :

https://maps.googleapis.com/maps/api/distancematrix/json?destinations=New%20York%20City%2C%20NY&origins=Washington%2C%20DC%7CBoston&units=imperial&key=YOUR_API_KEY

Obviously you need to replace "YOUR_API_KEY" with your API key from Google for which you need a billing account set up and Maps Javascript API enabled. The full set of optional parameters are described below. You will receive a response in JSON format (or XML if you replace json? with xml? that you need to parse. An example of some PHP code to parse a Distance Matrix API request is shown below. All the information you need can be found at Distance Matrix API request and response  |  Google for Developers[^].

<?php
// We need to get the JSON response into a string variable $jsonResponse
// First assign the URL of the Distance Matrix API request to a string
$url = 'href="https://maps.googleapis.com/maps/api/distancematrix/outputFormat?parameters';

// Use file_get_contents() to send a GET request to the URL
$jsonResponse = file_get_contents($url);

// Decode the JSON response
$data = json_decode($jsonResponse, true);

// Check if the status is OK
if ($data['status'] == 'OK') {
    // Loop through each row (origin-destination pair)
    foreach ($data['rows'] as $row) {
        // Loop through each element (information about the origin-destination pair)
        foreach ($row['elements'] as $element) {
            // Check if the status is OK
            if ($element['status'] == 'OK') {
                // Get the distance and duration
                $distance = $element['distance']['text'];
                $duration = $element['duration']['text'];

                // Print the distance and duration
                echo "Distance: $distance\n";
                echo "Duration: $duration\n";
            } else {
                echo "Error: " . $element['status'] . "\n";
            }
        }
    }
} else {
    echo "Error: " . $data['status'] . "\n";
}
?>

Distance Matrix API Request :
https://maps.googleapis.com/maps/api/distancematrix/outputFormat?parameters

Where outputFormat may be either json or xml.

And parameters include :

origins
The starting point for calculating travel distance and time. You can supply one or more locations in the form of an address, latitude/longitude coordinates, or a place ID.
destinations
One or more locations to which to calculate travel distance and time.
mode (optional)
Specifies the mode of transport. Options include driving, walking, bicycling, and transit.
units (optional)
Specifies the unit system to use when expressing distance as text. Options include metric and imperial.
departure_time (optional)
Specifies the desired time of departure as an integer in seconds since midnight, January 1, 1970 UTC.
traffic_model (optional)
Specifies the assumptions to use when calculating time in traffic. Options include best_guess, pessimistic, and optimistic.

Mike