For many of our products we provide templates that are available on our website to ensure your images are a perfect match for the product. You can find them here:

If you then download the template for the product and size that you're creating, it will highlight how much of the image is used as bleed.

Once you're happy, you can then save your image and remove the guide layers before using it to create your products. If you're intending to offer multiple sizes, we would recommend doing this for the largest size you expect to offer, as our API can then scale the image down for the smaller sizes, to save you repeating these steps for each one.