A dildo is a sex toy, often explicitly phallic in appearance, intended for sexual penetration or other sexual activity during masturbation or with sex partners. Dildos can be made from a number of materials and shaped similarly to an erect human penis. They are typically about the average length of an erect penis, 4–6 inches (10–15 cm), but some may be longer. A dildo's circumference is typically 4–5 inches (10–13 cm).