Sum array values

$total_weight = 0;
$json_string = '{ "rate":{ "items":[ { "name":"My Product 3", "sku":null, "quantity":1, "grams":1000, "price":2000, "vendor":"TestVendor", "requires_shipping":true, "taxable":true, "fulfillment_service":"manual" }, { "name":"My Product 1", "sku":null, "quantity":1, "grams":500, "price":1000, "vendor":"TestVendor", "requires_shipping":true, "taxable":true, "fulfillment_service":"manual" }, { "name":"My Product 2", "sku":null, "quantity":1, "grams":2000, "price":3000, "vendor":"TestVendor", "requires_shipping":true, "taxable":true, "fulfillment_service":"manual" } ], "currency":"CAD" }}';
$json_data = json_decode($json_string, true);

$max_weight = 10000;
foreach($json_data['rate']['items'] as $key => $value)  {
    $total_weight += $value['grams'];
}

echo $total_weight; // 3500
// then just compare whatever $max_weight value has to $total_weight
// rest of your desired code

// Convert the raw json to an array with json_encode & the 'true' option.
$json_array = json_decode($raw_json, true);

// Now use array_map to return and array of just the value of grams.
$grams_array = array_map(function ($item) { return intval($item['grams']); }, $json_array['rate']['items'] );

// Echo the sum of the grams array with by using array sum.
echo array_sum($grams_array);

// Set the raw JSON.
$raw_json = <<<EOT
{
   "rate": {
       "items": [
           {
               "name": "My Product 3",
               "sku": null,
               "quantity": 1,
               "grams": 1000,
               "price": 2000,
               "vendor": "TestVendor",
               "requires_shipping": true,
               "taxable": true,
               "fulfillment_service": "manual"
           },
           {
               "name": "My Product 1",
               "sku": null,
               "quantity": 1,
               "grams": 500,
               "price": 1000,
               "vendor": "TestVendor",
               "requires_shipping": true,
               "taxable": true,
               "fulfillment_service": "manual"
           },
           {
               "name": "My Product 2",
               "sku": null,
               "quantity": 1,
               "grams": 2000,
               "price": 3000,
               "vendor": "TestVendor",
               "requires_shipping": true,
               "taxable": true,
               "fulfillment_service": "manual"
           }
       ],
       "currency": "CAD"
   }
}
EOT;

// Convert the raw json to an array with json_encode & the 'true' option.
$json_array = json_decode($raw_json, true);

// Now use array_map to return and array of just the value of grams.
$grams_array = array_map(function ($item) { return intval($item['grams']); }, $json_array['rate']['items'] );

// Echo the sum of the grams array with by using array sum.
echo array_sum($grams_array);

var_export(
    array_sum(
        array_column(
            $array['rate']['items'],
            'grams'
        )
    )
);

3500