The three values

The labels are WooCommerce’s own, so they follow your shop’s language and any wording you have changed. Each has a count, and a status that no product has can be hidden with Hide values with no products. Many shops hide Out of stock altogether, and the filter then has only In stock and On backorder to show.

Why In stock is special

For a simple product, in stock means what it says. For a variable product, it can mean the parent is in stock because one size is, while the colour you chose is gone. When In stock is chosen, Siftwren asks WooCommerce to look at each variation’s own stock for that request, so the hoodie with only a sold-out red is no longer a red, in-stock hoodie.

Does your filter count the parent?

Change which variation is sold out and see the two ways of counting side by side. Nothing you type leaves this page.

Checkboxes, radio buttons or dropdown

Checkboxes let a shopper combine statuses. A radio button gives a plain either-or, and a dropdown takes less room in a narrow sidebar. All three produce the same address, filter_stock_status=instock, so you can change the display later without breaking links.

One practical point: if your shop only sells what it has, the stock filter is clutter. Leave it out of the set. If it sells made-to-order and in-stock items side by side, it is the single most useful filter on the page.