Curated OER
Math2.org: Areas, Volumes, Surface Areas
This personal site from Math2.org gives formulas for the area, volumes and surface areas of various shapes. Also provides diagrams.
Curated OER
Find Out Things About a Square
Webmath will calculate the side length, diagonal length, perimeter, area, or volume, given the side, perimeter, diagonal, or area. This site also displays formulas for a square.