Drop iPhone HEIC photos. Each is turned upright and written as PNG, which keeps every decoded pixel — and is large, so the byte count is shown before you save. HEIC opens here in browsers that read it themselves: Safari on Mac, iPhone and iPad.
Which browsers can open HEIC here
This site converts only with what your browser can do itself and never sends a photo anywhere to be decoded. Safari on a Mac, iPhone or iPad reads HEIC natively, so HEIC to PNG works there in full. Chrome, Edge and Firefox on Windows, Android and Linux do not read HEIC; on those browsers the file is listed with that reason rather than a broken result.
PNG is lossless and large
A 12-megapixel iPhone photo as PNG is commonly 15 to 25 MB — ten or more times the HEIC — because PNG keeps every pixel exactly and photographs compress badly without loss. The PNG's real size is shown next to the HEIC before anything is saved. If the photo is going to a portal or a chat, JPEG is usually the better answer; the page says so beside the result.
The photo is turned upright using the camera's orientation, and the GPS position and other EXIF data are not written into the PNG. Colour is converted to sRGB.