How do I convert HEIC photos to JPG on my iPhone?

Robert Shoens wrote:

I have about a 1000 such pics, not very practical.

Do you actually need to convert all of the 1000 photos to jpeg at once? If so, then you will need a 3rd party app for that and most likely a computer (Apple's Photos on Mac can do this easily after they are imported into the library).

Otherwise, when you need to use them as JPEG, select the photos you want to convert by tapping on the "Select" option in the photos app and marking each photo you want to convert, then tap on the share icon and then on the app you wish to use them with. You can send more than one photo at a time, and they will be converted.

Some apps in the list may stop being an option after a certain amount of photos are selected.

And if you absolutely need your photos to be in jpeg format, I second Old Toad's suggestion to set the Format option in Camera Settings to "Most Compatible" and any photos taken through the Camera App will be saved as jpeg from then on. It won't convert the existing ones though.

Use the Share icon in the Photos app to send it to another App such as the Mail app, and it will convert it to jpeg before sending it or using it in the selected App.

The HEIC format is to save space on mobile devices. So keep them as HEIC and when you use them outside of the iPhone via email convert them as Phil0124 suggested or use one of the apps from the App Store.

And for future photos change the format on the iPhone/iPad to "Most Compatible" which is jpeg.

There are a number of apps on the iOS App Store for converting HEIC photos to jpeg photos. I've never used any of them so you'll have to do your own due diligence.