If you create an abundance of art you will find you must frequently measure out your canvas size. To save time and possible errors, I cut out a set of templates in standard sizes.
Each template is labeled with the size and has a hole punched at the top for easy storage inside the art closet.
Keep a look out for old painted cabinets on the curb on trash pick-up day. Carry them home, bind the raw edges with duct tape, and you have a perfect waterproof board for mounting watercolor or acrylic paper/canvas.
A full sheet of plexiglass makes a durable and light mounting board for your larger size paper/canvas sheets. Painter’s tape/blue tape works perfectly with plexiglass and keeps your paper stable and flat until you are ready to remove it.