3-1/2 inches high x 4 inches wide. Iron-on patches are a novelty item. The iron-on backing should not be relied on to stick to all fabrics. It should be used for temporarily placement before sewing. Any fabric needs to be washed and clean before patch placement. Iron heat should be at a low setting and there should be no dampness to fabric or steam from iron. Iron should be pressed for 6-8 seconds to the patch for adherence. If patch does not stick, then your fabric is unsuitable for the iron-on backing.