You can find your iPhone/iPad model number by looking at the small text on the back of the device. There should be something that says "Model AXXXX".
You can reference the official Apple links at the bottom of this article to determine which iPhone/iPad model you own.
If you are having difficulty reading the text on the back there is another way to look this up. Open the iOS Settings app and navigate to General > About > Model (or Model Number). Tap once on Model to reveal the model number.
- Apple's official iPhone model list here.
- Apple's official iPad model list here.