Remove USPS Flat Rate envelopes with a code snippet

Use this developer customization when you want USPS Flat Rate boxes to remain available but do not want USPS Shipping Method to use its built-in Flat Rate envelope definitions.

Before you begin

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• This snippet requires USPS Shipping Method.
• Add the code with a site-specific plugin, a child theme, or a code snippet manager.
• Test the change on a staging site before using it on a live store.

Customizations are not covered under our support policy, so this isn’t something we can help implement or troubleshoot on your site.

Remove Flat Rate envelopes

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The wc_usps_flat_rate_boxes filter receives the built-in Flat Rate package definitions. This snippet removes the domestic and international envelope definitions while leaving the box definitions unchanged.

/**
 * Remove USPS Flat Rate envelope definitions while retaining Flat Rate boxes.
 *
 * @param array<string, array<string, mixed>> $flat_rate_boxes USPS Flat Rate package definitions.
 * @return array<string, array<string, mixed>>
 */
function wccom_remove_usps_flat_rate_envelopes( $flat_rate_boxes ) {
	$envelope_ids = array(
		'd13',
		'd16',
		'd29',
		'd30',
		'd38',
		'd40',
		'd42',
		'd44',
		'd63',
		'i8',
		'i13',
		'i29',
		'i30',
		'i63',
	);

	return array_diff_key( $flat_rate_boxes, array_flip( $envelope_ids ) );
}
add_filter( 'wc_usps_flat_rate_boxes', 'wccom_remove_usps_flat_rate_envelopes' );

This snippet was reviewed against USPS Shipping Method 5.6.1. If USPS adds another Flat Rate envelope definition, add its package ID to the $envelope_ids array.

For the standard package and box-packing settings, see Box Packing in the USPS Shipping Method guide.