[SOLVED] Set quantity minimum, maximum and step at product level in Woocommerce

Updated December 2020

The following revisited code will allow in addition to handle quantity steps.

I have changed quantity fields settings location to "General" settings tab.

I have added a checkbox that enables or disables those additional quantity settings at product level (showing or hiding the setting fields dynamically):

When checkbox unchecked (fields are not visible and quantity settings are disabled):

When checkbox is checked (fields are visible and quantity settings are enabled):

I have merged all settings in a unique custom field as an indexed array of values, to improve performance.

Since WooCommerce version 3, things have changed a lot, so I have made some changes enhancing and updating code to something more newer.

Also works nicely on Ajax add to cart for simple products, for product variations from variable products and also on the cart quantity input field.

All the code:

// Displaying quantity setting fields on admin product pages
add_action( 'woocommerce_product_options_pricing', 'wc_qty_add_product_field' );
function wc_qty_add_product_field() {
    global $product_object;

    $values = $product_object->get_meta('_qty_args');

    echo '</div><div class="options_group quantity hide_if_grouped">
    <style>div.qty-args.hidden { display:none; }</style>';

    woocommerce_wp_checkbox( array( // Checkbox.
        'id'            => 'qty_args',
        'label'         => __( 'Quantity settings', 'woocommerce' ),
        'value'         => empty($values) ? 'no' : 'yes',
        'description'   => __( 'Enable this to show and enable the additional quantity setting fields.', 'woocommerce' ),
    ) );

    echo '<div class="qty-args hidden">';

    woocommerce_wp_text_input( array(
            'id'                => 'qty_min',
            'type'              => 'number',
            'label'             => __( 'Minimum Quantity', 'woocommerce-max-quantity' ),
            'placeholder'       => '',
            'desc_tip'          => 'true',
            'description'       => __( 'Set a minimum allowed quantity limit (a number greater than 0).', 'woocommerce' ),
            'custom_attributes' => array( 'step'  => 'any', 'min'   => '0'),
            'value'             => isset($values['qty_min']) && $values['qty_min'] > 0 ? (int) $values['qty_min'] : 0,
    ) );

    woocommerce_wp_text_input( array(
            'id'                => 'qty_max',
            'type'              => 'number',
            'label'             => __( 'Maximum Quantity', 'woocommerce-max-quantity' ),
            'placeholder'       => '',
            'desc_tip'          => 'true',
            'description'       => __( 'Set the maximum allowed quantity limit (a number greater than 0). Value "-1" is unlimited', 'woocommerce' ),
            'custom_attributes' => array( 'step'  => 'any', 'min'   => '-1'),
            'value'             => isset($values['qty_max']) && $values['qty_max'] > 0 ? (int) $values['qty_max'] : -1,
    ) );

    woocommerce_wp_text_input( array(
            'id'                => 'qty_step',
            'type'              => 'number',
            'label'             => __( 'Quantity step', 'woocommerce-quantity-step' ),
            'placeholder'       => '',
            'desc_tip'          => 'true',
            'description'       => __( 'Optional. Set quantity step  (a number greater than 0)', 'woocommerce' ),
            'custom_attributes' => array( 'step'  => 'any', 'min'   => '1'),
            'value'             => isset($values['qty_step']) && $values['qty_step'] > 1 ? (int) $values['qty_step'] : 1,
    ) );

    echo '</div>';
}

// Show/hide setting fields (admin product pages)
add_action( 'admin_footer', 'product_type_selector_filter_callback' );
function product_type_selector_filter_callback() {
    global $pagenow, $post_type;

    if( in_array($pagenow, array('post-new.php', 'post.php') ) && $post_type === 'product' ) :
    ?>
    <script>
    jQuery(function($){
        if( $('input#qty_args').is(':checked') && $('div.qty-args').hasClass('hidden') ) {
            $('div.qty-args').removeClass('hidden')
        }
        $('input#qty_args').click(function(){
            if( $(this).is(':checked') && $('div.qty-args').hasClass('hidden')) {
                $('div.qty-args').removeClass('hidden');
            } else if( ! $(this).is(':checked') && ! $('div.qty-args').hasClass('hidden')) {
                $('div.qty-args').addClass('hidden');
            }
        });
    });
    </script>
    <?php
    endif;
}

// Save quantity setting fields values
add_action( 'woocommerce_admin_process_product_object', 'wc_save_product_quantity_settings' );
function wc_save_product_quantity_settings( $product ) {
    if ( isset($_POST['qty_args']) ) {
        $values = $product->get_meta('_qty_args');

        $product->update_meta_data( '_qty_args', array(
            'qty_min' => isset($_POST['qty_min']) && $_POST['qty_min'] > 0 ? (int) wc_clean($_POST['qty_min']) : 0,
            'qty_max' => isset($_POST['qty_max']) && $_POST['qty_max'] > 0 ? (int) wc_clean($_POST['qty_max']) : -1,
            'qty_step' => isset($_POST['qty_step']) && $_POST['qty_step'] > 1 ? (int) wc_clean($_POST['qty_step']) : 1,
        ) );
    } else {
        $product->update_meta_data( '_qty_args', array() );
    }
}

// The quantity settings in action on front end
add_filter( 'woocommerce_quantity_input_args', 'filter_wc_quantity_input_args', 99, 2 );
function filter_wc_quantity_input_args( $args, $product ) {
    if ( $product->is_type('variation') ) {
        $parent_product = wc_get_product( $product->get_parent_id() );
        $values  = $parent_product->get_meta( '_qty_args' );
    } else {
        $values  = $product->get_meta( '_qty_args' );
    }

    if ( ! empty( $values ) ) {
        // Min value
        if ( isset( $values['qty_min'] ) && $values['qty_min'] > 1 ) {
            $args['min_value'] = $values['qty_min'];

            if( ! is_cart() ) {
                $args['input_value'] = $values['qty_min']; // Starting value
            }
        }

        // Max value
        if ( isset( $values['qty_max'] ) && $values['qty_max'] > 0 ) {
            $args['max_value'] = $values['qty_max'];

            if ( $product->managing_stock() && ! $product->backorders_allowed() ) {
                $args['max_value'] = min( $product->get_stock_quantity(), $args['max_value'] );
            }
        }

        // Step value
        if ( isset( $values['qty_step'] ) && $values['qty_step'] > 1 ) {
            $args['step'] = $values['qty_step'];
        }
    }
    return $args;
}

// Ajax add to cart, set "min quantity" as quantity on shop and archives pages
add_filter( 'woocommerce_loop_add_to_cart_args', 'filter_loop_add_to_cart_quantity_arg', 10, 2 );
function filter_loop_add_to_cart_quantity_arg( $args, $product ) {
    $values  = $product->get_meta( '_qty_args' );

    if ( ! empty( $values ) ) {
        // Min value
        if ( isset( $values['qty_min'] ) && $values['qty_min'] > 1 ) {
            $args['quantity'] = $values['qty_min'];
        }
    }
    return $args;
}

// The quantity settings in action on front end (For variable productsand their variations)
add_filter( 'woocommerce_available_variation', 'filter_wc_available_variation_price_html', 10, 3);
function filter_wc_available_variation_price_html( $data, $product, $variation ) {
    $values  = $product->get_meta( '_qty_args' );

    if ( ! empty( $values ) ) {
        if ( isset( $values['qty_min'] ) && $values['qty_min'] > 1 ) {
            $data['min_qty'] = $values['qty_min'];
        }

        if ( isset( $values['qty_max'] ) && $values['qty_max'] > 0 ) {
            $data['max_qty'] = $values['qty_max'];

            if ( $variation->managing_stock() && ! $variation->backorders_allowed() ) {
                $data['max_qty'] = min( $variation->get_stock_quantity(), $data['max_qty'] );
            }
        }
    }

    return $data;
}

Code goes in functions.php file of your active child theme (or active theme). Tested and works.