Experts are divided on what the standard canvas size associated with web design out to be, with some arguing that it really doesn’t matter. However, for beginners, it is advisable to choose the common screen resolution of 1280×800, or 1920×1080.
However, for advanced designers, it is advisable to double this resolution, particularly if your design is intended for 2x displays for Macbooks, or triple it if the design is intended for android flagship devices. However, this is not entirely necessary, save for making your design look good when it is displayed on these devices.
You also have the option of making your file even larger by adding a browser window in the mock up. In these advanced settings, the canvas size is 4480px wide. The beauty around Photoshop is that it allows for a range of widths, ranging from 960 to 1200 pixels, normally. One factor to always appreciate it that your canvas should allow for expansion, particularly on the various monitors.
Therefore, the canvas size ideally needs to be 960 pixels. The height of the canvas is subject to the content within it. In order to achieve the standard 4:3 aspect ratio typical in standard monitors, you may consider a resolution of 720 pixels, 800 pixels for tablets, and 320 pixels for mobile. The important thing is to remain as flexible as possible.