Square Me Up Ruler uses 10in squares to make 4in finished size half-square triangles. Use prepackaged 10in squares or cut four 10in squares from 1/3 yard of fabric. Also makes 1 1/2in size half-square triangles from 5in squares of fabric. A fun tool that measures 7-1/2in x 7-1/2in. Non-slip coating on the back makes it easy to use.