Pipeline allows you to configure a Shopify page as a pop-up for all your products:
For best results, create a size chart page in your Shopify Admin which includes a wide range of sizes. Use that page as your size chart page option.
Begin by creating a page in the Shopify Admin under Online Store -> Pages:
Next, in the Theme Editor. Navigate to any product or use the top drop-down and choose Default product. Click on Product page, the optional sizing popup settings are towards the bottom. Choose the page you created:
Products without a size variant will display the size-chart link lower down, just above the add to cart button and also styled as a badge. If many of your products are not using the size variant, you can repurpose this feature to be used as a badge with link to promotional or brand information: