Which is the lightest 256GB iPhone available?

Do you have any other requirements? iOS version compatibility, screen size, or anything else? If just weight, probably the iPhone 13 Mini is the answer. At 4.97 ounces it is the lightest. The SE 3rd Edition is 5.07 ounces.

Both will run iOS 18.

iPhone 12 mini - 4.76 ounces

iPhone 13 mini - 4.97 ounces

Both run iOS 18 and have 256gb storage available

iPhone 12 mini might be your desirable pick

Good info, but I would still suggest the 13 mini, as it will be supported longer than the 12. And it is a difference of only 0.21 ounces, the weight of about 1 teaspoon of sugar.