Identify your iPhone by referring to the model number printed on the back of the device.

iPhone 4: Model A1332 or A1349 (glass back)
iPhone 4S: Model A1387 or A1431 (glass back, Siri)
iPhone 5: Model A1428, A1429, or A1442 (aluminum back, 4” screen)
iPhone 5C: Model A1456, A1507, A1529, A1532, A1516 or A1526 (colored plastic back)
iPhone 5S: Model A1453, A1457, A1530, A1533, A1518, or A1528 (aluminum back, fingerprint reader)
iPhone 6: Model A1549, A1586, or A1589(4.7" screen)
iPhone 6 Plus: Model A1522, A1524, or A1593(5.5" screen)
iPhone 6S: Model A1633, Model A1688(4.7" screen)
iPhone 6S Plus: Model A1634, Model A1687(5.5" screen)